R E V I E W P A P E R
Sustainable intensification in the production of grass and
forage crops in the Low Countries of north-west Europe
D. Reheul
1| M. Cougnon
1| M. Kayser
2| J. Pannecoucque
3| J. Swanckaert
1,3|
B. De Cauwer
1| A. van den Pol-van Dasselaar
4| A. De Vliegher
31
Department of Plant Production, Faculty of Bioscience Engineering, Gent University, Gent, Belgium
2
Department of Crop Sciences - Grassland Science, Georg-August-University G€ottingen, G€ottingen, Germany
3
Institute for Agricultural and Fisheries Research ILVO, Merelbeke, Belgium
4
Wageningen Livestock Research, Aeres University of Applied Sciences, Dronten, The Netherlands
Correspondence
D. Reheul, Department of Plant Production, Faculty of Bioscience Engineering, Gent University, Gent, Belgium.
Email: dirk.reheul@ugent.be
Abstract
Production of grass and fodder crops in areas under intensive production systems in
the Low Countries of north-west Europe faces a number of threats related to
increased regulations, scarcity of land and restricted freedom of use of the land, and
from climate change. Grassland-based farmers are pushed to do more with less, i.e.,
to improve eco-efficiency, and this requires
“more knowledge per ha.” This article
argues that progress in variety breeding, the application of crop rotation instead of
monocultures, a proper use of catch crops, ley-arable farming and overall good
man-agement offer realistic opportunities to cope with current threats. A large capacity
for mechanization also allows improvement of net yields per ha. This article
high-lights that progress in plant breeding has compensated for yield declines caused by
nutrient-input restrictions in forage maize (Zea mays L.). Both forage maize and
grass
–clover can take advantages of ley-arable farming, and crop rotation provides
an insurance against the effects of low-yielding years and a buffer for reduced
nutrient inputs.
K E Y W O R D S
cropping systems, good agricultural practices, grassland farming, ley-arable farming, mechanization, progress by plant breeding, yield gap
1
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I N T R O D U C T I O N
Economic, ecological and societal changes are presenting intensive animal-based farms in western Europe with several challenges. There is competition for land, particularly in the densely populated areas, resulting in high land prices. Prices are fluctuating depending on the region and the use of the land (arable or grassland), but prices for good-quality arable land in regions with intensive livestock production currently may reach 85,000€/ha and more in the north of Belgium, the Netherlands and north-west Germany. Governmental regulations regarding the use of grassland also influence the selling prices of grass-land: depending on the region, the quality of the land and the national regulations, prices in the Low Countries fluctuate between extremes of 25,000 and 90,000€/ha (Boerderij, 2016; GAG, 2016).
Fluctuating off-farm prices for milk and meat are pushing farmers to reduce their costs. One important way to cut input costs is by
producing more farm-grown forage of high quality. However, avail-able land is scarce, competition for land is strong, and prices are high, thus hampering the acquisition of more land. An alternative is to enhance productivity on the available land area, but there is con-tinuous tightening of legal restrictions regarding land use and envi-ronmental loadings. Thus, there are now no easy ways (e.g., by increasing nutrients) for farmers to increase yields. Moreover, climate change is influencing crop performances, both directly from the effects of changing weather patterns, and also indirectly, due to emerging policies that aim to mitigate climate change. Changing weather patterns also increase risks in crop production. Policies aimed at mitigating climate change usually lead to higher production costs or impose further restrictions. Crop production is also subject to changes in the attitudes of European consumers, which may lead to lower domestic consumption of animal products or to a greater demand for“non-commodities.” As a consequence of these ongoing
Received: 28 October 2016
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Revised: 24 January 2017 DOI: 10.1111/gfs.12285developments, farmers in intensive systems must find ways to inten-sify their production by applying production systems that are com-patible with environmental and societal changes and that also result in a minimum of environmental disturbance. Essentially, this means improving eco-efficiency. For the definition of eco-efficiency, we refer to Ehrenfeld (2005) and Huppes and Ishikawa (2005a,b). According to Keating et al. (2010), improving eco-efficiency in agri-culture is about“doing more with less.” Alternatively, one may call this process“sustainable intensification.” There are several contest-ing definitions of sustainable intensification (Garnett & Godfray, 2012). However, sustainable intensification in agriculture is well defined in the 3rd SCAR Foresight Exercise (Freibauer et al., 2011): “producing more food from the same area of land while reducing the environmental impacts.” According to Buckwell et al. (2014) sustain-able intensification in agriculture comes down to“more knowledge per ha.”
In this review, we provide ideas and evidence to underpin the hypothesis that the concept of“more knowledge per ha” offers good opportunities to improve eco-efficiency. In particular, we argue that the combination of advances in plant breeding with well-designed cropping systems and crop rotations, supported by the benefits of field mechanization, is a way to improve eco-efficiency.
1.1
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Interpreting the production function
The relation between crop yield and the amount of input factors needed for that yield is given by the Mitscherlich equation, known as the“law of diminishing increments” and graphically presented as an asymptotic yield curve (Sorensen, 1983). Shifting the yield curve upwards simply means that one produces more with less. There are different ways to realize an upward shift: either by genetic crop improvement or by optimizing the production through application of good managerial practices (and/or good crop husbandry). Both of these interfere with the use efficiencies of input factors, e.g., nutri-ents. Some general reflections on the concept of use efficiencies, specifically in the context of maize, are given by Reich, Aghajadan-zadeh, and de Kok (2014) and Mueller and Vynn (2016).
Optimizing the productivity of a crop is directly related to an improved availability and acquisition of nutrients. Genetic crop improvement can extend the growing period and change crop physi-ological traits resulting in further enhancement of the intrinsic uti-lization efficiency or conversion efficiency of nutrients (i.e., the ratio of dry-matter [DM] yield/amount of acquired nutrients).
The effects of genetic improvements are usually constant for a given input, as illustrated by Kamprath, Moll, and Rodriguez (1982), Bugge (1988) and Sangoi, Ender, Guidolin, Luiz de Almeda, and Kon-flanz (2001). The upward shift of the yield curve in response to good managerial practices is usually shown as a visual shift to the left of the curve, as the effect of managerial practices declines at high inputs. Illustrative general examples can be found in Nevens and Reheul (2002a) and Wulfes, Manning, and Ott (2006). This can be summarized as follows: shifting the yield curve either to the left or upwards offers opportunities to produce more with less. The
question remains: “How does this work in forage crops and how large is the impact of both crop husbandry and genetic improvement?”
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F O R A G E M A I Z E
2.1
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Monocropping vs. crop rotation
Intensive dairy farms in the temperate regions of Europe rely pre-dominantly on two crops: grass and forage maize. The high level of interest in silage maize is related to its relative ease of growing, min-imal losses during harvest and conservation (van Dijk, Schukking, & van der Berg, 2015), and particularly to its high energy content, which has increased during the past decades. The newest varieties of maize have a starch content in the DM at harvest time that is about 20% higher than in varieties grown around the year 2000. The starch content, expressed as a percentage of DM, of many vari-eties released since 2005 is in the range of 35%–40% at harvest time for silage maize (35% DM; Cone, van Gelder, van Schooten, & Groten, 2008; Pannecoucque, van Waes, de Vliegher, & Jacquemin, 2015). Silage maize comprises about 50% (on DM basis) of the annual forage rations in the Low Countries.
Silage maize is grown either as a monocrop or in a very tight crop rotation on many farms, presenting a very convenient cropping system in terms of its economy and labour organization (van Eekeren et al., 2008). Provided that nutrient inputs are not too restricted, yields of silage maize continue to be high in monocropping systems. However, nutrient regulations move the production window away from the plateau of the yield curve. In consequence, crops become more sensitive to fluctuating environmental conditions in situations where the effects of bad agricultural practices cannot be offset by additional nutrient inputs (Hanegraaf, Hoffland, Kuikman, & Brussaard, 2009; Nevens & Reheul, 2003; Smith, Menalled, & Robertson, 2007).
Simple repetitive agricultural practices such as monocropping favour weeds that are closely related to the crop (Murphy & Lemerle, 2006). Unvarying cropping environments allow easy adapta-tion of weeds to their control strategies (Harker, 2013). Maize monocropping has entailed flora and weed shifts from broadleaved weeds to panicoid grasses and favoured the development of herbi-cide-resistant biotypes of several weed species, e.g., the dicot spe-cies Chenopodium album L. and Solanum nigrum L. that became resistant to atrazine in the mid-1980s. From the point of view of a farmer, in the years since 2010 the weed flora of maize has shifted from an easily controllable, species-rich and well-balanced flora to a less easily controllable, unstable and species-poor flora dominated by panicoid grasses. According to Claerhout, Reheul, and de Cauwer (2015), weed populations in maize monocropping systems were up to 14% less sensitive to foliar-applied maize herbicides than popula-tions in cropping systems with maize in crop rotation. Furthermore, crop rotations offer opportunities to fight some expanding pests, like different species of soil nematodes and the western corn rootworm (Diabrotica virgifera virgifera). They also allow a more sustainable soil
management (Lal, 2008, 2009) resulting in a better management of soil organic matter and of nutrient dynamics (Thorup-Kristensen, 2006, 2012; Kayser, Seidel, M€uller, & Isselstein, 2008; Kayser, M€uller, & Isselstein, 2010; Spiertz, 2010).
Borrelli, Castelli, Ceotto, Cabassi, and Tomasoni (2014) reported results of experiments with several cropping systems over a 26-year period on a sandy loam soil in the lowland of the Po Valley of north-ern Italy. Silage maize was tested in an annually repeated double-crop system (silage maize followed by Italian ryegrass (Lolium multi-florum L.) in the autumn; both crops harvested for silage) and com-pared with a 3-year rotation (year 1: grain maize; year 2: autumn-sown winter barley followed by silage maize (both harvested for silage); year 3: autumn-sown Italian ryegrass followed by silage maize (both harvested for silage)) and with a 6-year rotation (first 3 years: silage maize followed by autumn-sown Italian ryegrass, last 3 years: ley). The crops were managed either (i) following farmers’ practices or (ii) with 30% less nutrient inputs and 25% less herbicide inputs. The most important conclusion of the experiment was that year-to-year variability was overwhelming, compared with the effect of the treatments, and that the effects of crop rotation and nutrient input were more pronounced in low-yielding years. Borrelli et al. (2014) concluded that the rotation effect can compensate for a reduced input and that the adoption of rotation can be regarded as an insur-ance against low-yielding years. In other words, crop rotation improved yield stability; and the longer the rotation, the better the yield stability. Enhancing the yield stability in crop production is also an important issue in the light of climate change and the prediction of increased occurrence of extreme weather effects.
Wulfes and Ott (2008), working on a loamy sandy soil in north-ern Germany, compared forage maize in monocropping with maize followed by winter wheat and winter barley followed by oilseed rape (Brassica napus L.) as a catch crop. The experiment lasted 3 years; N-fertilization was 0, 80, 110 or 160 kg/ha. At the start of the experiment, all three crops featured as openers of the rota-tion; during the two consequent years the other crops followed in the designed order. Both cereals were harvested as whole-crop silage. As indicated in Figure 1, DM yield, N yield, NEL and CP were substantially higher in rotated maize, irrespective of the N-dressing.
Nevens and Reheul (2002a) compared silage maize grown in rotation with faba bean (Vicia faba L.) and fodder beet (Beta vulgaris L.) with maize grown in monocropping during a period of over 12 years on a soil classified as silt loam (USDA soil texture classifica-tion) in Belgium. Crops were grown either on arable land continu-ously cropped with annual crops or in a ley-arable system (3 years grassland followed by 3 years arable land) and fertilized with differ-ent N levels. When grown on arable land continuously cropped with annual crops, maize in rotation outyielded maize in monocropping significantly in 80% of the cases. The yield bonus (both DM yield and N yield) was small to nearly absent at an input of 180 kg N ha 1, but was approximately 25% at 75 kg N ha 1. The
effect on DM yield of crop rotation was marginal in the ley-arable system.
The inclusion of fodder beet in their crop rotation was very favourable for the environment as this crop depleted the soil very effectively, thereby resulting in residual mineral soil nitrogen of less than 50 kg N ha 1 in a soil profile of 0
–90 cm irrespective of the applied N-fertilization. Carlier and Verbruggen (1992) studied nitro-gen balances on 61 Flemish dairy farms and concluded that farms that produced fodder beet had by far the lowest nitrogen surplus at the farm level.
Growing fodder beet continues to be a challenge, although some of the drawbacks are now better manageable than in the past dec-ades. The more frequent occurrence of mild winters in temperate regions of Europe may facilitate conservation of the fresh beet. Co-ensiling ground beet with silage maize may take away the concerns regarding storage of fresh beets over winter but requires the har-vesting of both crops to be synchronized. The performance of dairy cows fed with this forage-mix remain at very high levels provided the proportion of fodder beet in the silage is approximately 25% (on DM basis) and contamination with soil is low (de Brabander, Vanacker, Andries, de Boever, & Buysse, 1989). Techniques used to clean sugar beets can be used to remove most of the soil from fod-der beet. Seed companies are now offering “high DM” (20%–23% DM) fodder beet to be co-ensiled with forage maize. The higher the DM content, the higher the yield potential. Apart from its environ-mental value and feeding value, fodder beet may be a good candi-date as a third crop to fulfil the latest CAP (Common Agricultural Policy) demands. However, the perspectives of growing fodder beet in a crop rotation may be hampered by the rapid spreading of the plant pathogenic fungus Rhizoctonia solani, which is infecting fodder and sugar beet as well as maize and ryegrasses (Heremans, Garrido, & Haesaert, 2007). We observed very important losses during winter conservation of fodder beets, produced in a long-term field trial at the University of Ghent (Belgium). Fodder beet was grown in a 4-year crop rotation: fodder beet–silage maize–Brussels sprouts–potato followed by Italian ryegrass as a cover crop (D’Hose et al., 2012). Rotten biomass due to Rhizoctonia solani measured in January 2016 was in the range of 30% to 80% (Ghent University, unpublished results); losses depended on the level of N: the higher the N-fertili-zation, the lower the infection. We concluded that without using a Rhizoctonia-tolerant variety, growing fodder beet in this rotation was no longer of value. These observations are supported by many expe-riences from practice, indicating that losses in the field and during conservation are frequently unacceptably high without Rhizoctonia-tolerant cultivars. Currently only a few Rhizoctonia-Rhizoctonia-tolerant varieties of fodder beet are available in Europe.
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The role of forage maize breeding
Long-term analyses of the genetic progress in silage maize varieties tested in the German official variety trials show a more or less steady annual progress in DM yield of approximately 200 kg/ha dur-ing the period 1983–2012 (Laidig, Piepho, Drobek, & Meyer, 2014; Piepho, Laidig, Drobek, & Meyer, 2014) and of 153 kg/ha during the period 1992–2012 in the Belgian official variety trials (unpublished
data). There are no signals that this progress is likely to be slowing down in the forthcoming European varieties. In terms of nutrient efficiency we may ask whether these newest, highly productive for-age maize varieties take up more nitrogen than varieties from pre-vious decades. From an environmental point of view this is relevant, as a higher uptake would result in lower residual soil nitrogen. Barriere et al. (1997) found a negative correlation (r= .45) between N-content and biomass yield in 126 early hybrids in France but, according to several European silage maize breeders, there are currently no indications that yield progresses are necessarily accompanied with a dilution of nitrogen in the DM. The latter was confirmed by an analysis of the Belgian official vari-ety trials during the period 2003–2010 applying the methodology of Chaves, de Vliegher, van Waes, Carlier, and Marynissen (2009) and Rijk, van Ittersum, and Withagen (2013). Over this period of time, new candivars yielded on average approximately 10% more DM than the reference variety“Banguy,” first tested in the Belgian official variety trials in 1992 (Figure 2a). Their N-content (%N of DM) was similar to that of Banguy (Figure 2b); as a result, their N-uptake was about 10% higher (Figure 2c) as was their Nitrogen Utilization Efficiency (kg DM (kg acquired N) 1). N-uptakes varied between 240 and 260 kg/ha at N-fertilizations of about 200 kg/ha
in these trials. This means that modern varieties export about 25 kg more N than varieties of earlier decades. However, it is not only the amount of exported N but also the time of uptake (early or late in the growing season) that is environmentally relevant. Indeed, according to Coque and Gallais (2007) and Mueller and Vynn (2016) the most recent maize varieties take up more N after silking (in the Low Countries, this means from the end of July onwards) than older varieties. Because photosynthetic tissues in recent “stay-green” hybrids have a prolonged activity, roots con-tinue to receive part of the assimilates, while the majority are going to the grains which are the strongest sinks (He, Osaki, Takebe, & Shinano, 2003). As a consequence, root activity and N-uptake can remain high during the grain-filling period. This post-silking N may partly originate from mineralized soil organic matter (as the rate of mineralization follows soil temperature and mois-ture), and this would further reduce the residual soil nitrogen after harvest. In field tests in the north of France with 18 hybrids, regis-tered between 1991 and 2002, the average post-silking N-uptake was 28% of total N absorbed at maturity (205 kg/ha) with a varia-tion between 10% and 30% (Coque & Gallais, 2007). After fertiliza-tion, 200 kg/ha mineral N had been available in these trials. According to Kosgey, Moot, Fletcher, and McKenzie (2013), the
F I G U R E 1 Effect of crop rotation on the performance of silage maize at different amounts of N-fertilization in northern Germany. Adapted from Wulfes and Ott (2008)
average post-silking N-uptake of four hybrids in New Zealand was 42% (varying between 30% and 50%) of the N-uptake at full matu-rity (207 kg/ha); N-fertilization had been 135 kg/ha. Mueller and Vynn (2016) performed a meta-analysis of 86 published field exper-iments with mainly non-European genotypes from all over the world. Average post-silking N-uptake represented 36% of total plant N at maturity in 427 genotypes registered between 2001 and 2014, whereas it was 30% in 281 genotypes released before 1991; N-fertilization in all cases had been approximately 170 kg/ha.
Unfortunately, the genetic progress in yield is not fully capital-ized. Agronomic changes (e.g., due to restrictions on the input side, altered management techniques and climate effects) are preventing maximal yields. Laidig et al. (2014) showed that in Germany the genetic progress was nearly completely undone by agronomic changes during the period 1987–2012. The result was that, thanks to genetic progress, yields in experimental fields at the end of the studied period had not declined compared to the past decades. In addition to that, there is a yield gap between those obtained in well-F I G U R E 2 Trends in performances of
forage maize varieties in the Belgian official variety trials. All trends are expressed relative to the performances of the variety“Banguy” which was used as a reference variety during the complete testing period. (a) DM yield, (b) N-content, (c) N-export. Each point represents the performance of a new candidate variety, averaged over multiple Belgian locations during 3 years. All performances of a variety are allocated to the first year of entry in the trials
maintained scientific trials and actual farming practices. Laidig et al. (2014) reported yield gaps between research and farming in Ger-many of about 15 tons of fresh harvested biomass (40 vs. 55 t/ha). Therefore, to obtain the maximum possible advantage of the genetic progress, improved agronomic practices are needed. This combina-tion would compensate for restriccombina-tions in crop produccombina-tion posed by regulations and climate change.
The message is clear: (i) modern silage maize varieties have a high yield potential, and (ii) they extract more N from the soil than older ones, theoretically leaving less residual soil nitrogen after har-vest, but (iii) part of this potential cannot be capitalized due to dif-ferent kinds of restrictions and suboptimal management practices. To put this another way, thanks to plant breeding, current yields have not declined.
2.3
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Catch crops after silage maize
The role of catch crops is essential to reduce nutrient losses and to guarantee a good eco-efficiency. How much nitrogen they recover depends on the quantity of N left in the soil, the length of their growing period and weather conditions. Comprehensive data on catch crops are given by van Dam (2006). Timely sown catch crops can reduce N-leaching during the winter in forage maize fields by approximately 50% (Schr€oder, 1998; Wachendorf, Volkers, Loges, Rave, & Taube, 2006a; Wachendorf et al., 2006b). Cover crops need to be sown early to be effective. Komainda, Herrmann, Kluss, and Taube (2015) reported results of a 2-year experiment on a silty sand soil in northern Germany with Italian ryegrass and winter rye sown as cover crops after the harvest of forage maize. The growing condi-tions during these 2 years were very contrasting. They found an exponential relationship between N-uptake in the aboveground bio-mass (in the period between sowing and the time point where weather conditions become practically prohibitive for growth in November) and the temperature sum (degree9 days with base tem-perature 5°C): y = 0.2626 9 e0.0131x for Italian ryegrass (R2= .58, RMSE= 5.03) and y = 658 9 e0.0119x for winter rye (R2= .84,
RMSE= 5.85). Schr€oder, van Dijk, and de Groot (1996) and Schr€oder (1998) linearly regressed the N-uptake of the aboveground biomass in spring on the temperature sum (base temperature 5°C) starting from the sowing date (winter rye) or from the harvest date of the maize for Italian ryegrass that had been undersown in the first half of June on a sandy soil in the Netherlands. Averaged over the period 1988–1994 it took about 7 day 9 degrees to take up 1 kg N ha 1.
The long-term average daily temperature (1961–1990) in the period between 1 April and 30 September was 13.8°C; for the period 1 October until 31 March it was 4.9°C. In both the studies of Komainda (2015) and Schr€oder et al. (1996) and Schr€oder (1998), stubbles (to ground level) were included in the aboveground bio-mass. van Dam (2006) estimated the N-uptake capacity (kg/ha) of winter rye (root biomass included) under Dutch conditions until mid-March as: 949 (kg/ha) 3.3 (kg/ha/d)9 Y (d), where Y is the day of the year after 1 January between 220 and 275. According to this formula, winter rye sown on 25 September can take up
65 kg N ha 1. These studies did not consider the N in the roots,
which can be considerable. The proportion of root DM/total DM in a soil layer of 100 cm in November was estimated by Thorup-Kris-tensen (2001) in a Typic Agrudalf soil in Denmark: averages over 2 years were 0.32 for winter rye and 0.35 for Italian ryegrass. Cougnon, Vandermoere, de Vliegher, and Reheul (2015) measured root DM (in the upper 20 cm of the soil)/total DM ratios from the beginning of February until mid-April on a sandy loam soil in Bel-gium. Ratios varied from 0.38 to 0.55 for Italian ryegrass and from 0.29 to 0.45 for winter rye with the highest ratios recorded in mid-April.
There are few available sources of information on N concentra-tions in the roots of catch crops. van Dam (2006) reporting on Rhi-zolab studies with catch crops in the Netherlands, mentions 24 mg N (g DM) 1in roots of winter rye vs. 35 mg N (g DM) 1in
leaf sheath and stem, 39 mg N (g DM) 1 in dead leaves and
47 mg N (g DM) 1in green leaves. Taking into account the relative
proportions of the aboveground components, we arrive at an aver-age of about 40 mg N (g DM) 1 in the aboveground biomass. The root/shoot ratio for N concentration was about 0.6. According to Nichols and Crush (2007) this ratio is about 0.55 in Italian ryegrass. The latter data come from lysimeter trials in New Zealand with four varieties having N concentrations in the shoots and roots ranging between 1.45–1.64 and 0.72–1.00 respectively; the root/shoot DM ratios were 0.54 on average and the root DM/total DM ratio ranged from 0.30 to 0.55. Whitehead (1995) reports that fertilizer N usually has little effect on the production of grass roots but increases the concentration of N in the roots; N in roots of cut perennial ryegrass (Lolium perenne L.) ranged from 1.07% at no N to 1.64% at an N input with fertilizer of 400 kg N ha 1.
Based on the previous data, it is obvious that catch crops that are sown later than the beginning of October in the Low Countries have a very restricted N-uptake before winter, meaning that growing late-maturing forage maize varieties jeopardizes the success of catch crops. As early-maturing varieties are as much as 5%–10% less pro-ductive (unpublished data from Belgian official variety trials) than later maturing varieties, adopting a strategy to avoid N losses using earlier varieties in combination with catch crops implies a potential yield loss of 5%–10%. Although it may be hard in the short term not to grow the most productive maize varieties, the proactive use of an early-maturing variety followed by a timely installed catch crop, thus reducing N losses, may result in the prevention of a further tighten-ing of regulations on N losses.
At least two plant breeding companies in Europe are currently developing or testing non-GM herbicide-tolerant varieties of Lolium perenne and tall fescue (Festuca arundinacea Schreb.). The idea is to sow these grasses simultaneously with the silage maize and to have a well-established catch crop after harvest of the maize with no need for soil tillage, irrespective of adverse weather conditions. Owing to their herbicide tolerance, these grasses are affected by the maize herbicides but eventually they recover and survive. As a con-sequence, the competition with the growing maize is not too strong and they start growing vigorously immediately after the maize
harvest, provided they are not seriously damaged by the harvesting machines. Based on their slow establishment, deep rooting system and their tolerance to many herbicides, amenity types of tall fescue seem to be excellent candidates for simultaneous sowing with maize. However, competition is not completely eliminated: Cougnon, Claer-hout, de Frenne, de Cauwer, and Reheul (2016) reported results of 2 years of field trials with (mainly amenity types of) tall fescue and maize in Belgium and found a decline in yield of forage maize of between 8% and 19% depending on the year. These yield losses are unacceptably high. Research is in progress in different countries to improve the cohabitation of maize and grass (e.g., by changing the sowing density or the distance between rows of grass and maize) or to test other species like red fescue in Denmark (Manevski, Børge-sen, AnderBørge-sen, & KristenBørge-sen, 2015). A further disadvantage of under-sowing is that the maize stubbles remain more or less intact after harvest, as there is no tillage for establishment of a catch crop. As a result, the catch crop has little or no value as a feed in the following spring as it is contaminated with the low value debris of decaying maize stubbles and sand. In addition to the uptake of residual soil N, the value of the system is then in the supply of about 2,000 kg DM ha 1to the pool of soil organic matter upon ploughing down the catch crop after winter (Cougnon et al., 2016).
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L E Y - A R A B L E S Y S T E M S
As breaking-up grassland presents environmental risks and costs, extremely good care should be taken of good grassland swards to keep them in good shape for as long as possible. Only when the botanical composition is a factor that is limiting the utilization of high yields should the break-up of grassland swards be considered (Conijn, Velthof, & Taube, 2002). The consequences of grassland renovation for nutrient management recently have been reviewed by Isselstein and Kayser (2015). Extensive data are also provided by Schmeer (2012), Nevens (2003), Seidel, Kayser, M€uller, and Isselstein (2009) and Verloop (2013).
If it becomes necessary for a grassland sward to be broken up, consideration should be given to the timing of cultivation as spring ploughing causes less N-leaching than autumn ploughing (e.g., Sch-meer, 2012; Seidel et al., 2009). Spring ploughing allows the full use of the grassland in the year before ploughing and allows the installa-tion of a spring-sown crop immediately after ploughing, hence creat-ing the opportunity for a ley-arable production system.
An important characterization of ley-arable systems is the dynamics of soil organic matter (SOM): soil organic matter is built up during the ley phase and part of it is decomposed during the arable phase, resulting in a slow increase of the stock of SOM and provid-ing mineralized nutrients (mainly N) to subsequent crops (Vertes et al., 2007). The longer the ley phase, the more SOM is built up, but the accumulation rate is usually declining asymptotically, to reach an equilibrium. The time required to reach this equilibrium SOM content varies from a few years to more than a century depending on the initial SOM content and the soil (Johnston et al.,
1994). Hence, the most appropriate balance between length of ley and length of arable period in a ley-arable system is dependent of the local soil and climate conditions. From evidence in the literature one can conclude that in most circumstances encountered in lowland areas, the accumulation of near-maximum soil N occurs after 3 years ley (Christensen, Rasmussen, Eriksen, & Hansen, 2009; Deprez, Lam-bert, & Peeters, 2005; Eriksen, 2001; Eriksen, Askegaard, & Søegaard, 2008; Eriksen, Pedersen, & Jørgensen, 2006; Hansen, Erik-sen, & JenErik-sen, 2005; Johnston et al., 1994; Kayser, Benke, & Issel-stein, 2011, Kayser et al., 2008, Nevens and Reheul, 2002b; Webster, Poulton, & Goulding, 1999). Experimental results of Han-sen et al. (2005) indicate that organic N is easier to mineralize the more recently it has been formed. As a consequence, the effect of ploughing-out young grassland swards (1–3 years) on the N supply to the following crop, is already much reduced in the second year of arable cultivation. In addition, the risk of N-leaching after ploughing-out of grassland increases with the age of the sward (Eriksen et al., 2006). Therefore, taking into account the rapid decline in the amount of N mineralized after ploughing, the risk of nitrate leaching and the cost of installing grassland, both ley and arable intervals should not exceed 3 years.
3.1
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Advantages of ley-arable systems
Reheul, de Vliegher, Bommele, and Carlier (2007) and Bommele (2007) reported substantial differences in DM yield between renewed grassland and grassland sown into arable land. Grassland established on arable land significantly outyielded renewed grass-land (means of N-fertilizations of 100, 300 and 400 kg ha year 1)
during the first 2 years after the year of (spring) establishment. The DM yield bonus over a period of 3 years (year of establishment not included) was 10%; even at 400 kg N ha 1year 1 the bonus was
still 5%. It was even 20% in 2003, a year with a very dry summer. Hence, exploiting part of the grassland on a farm as temporary grassland can be an insurance against periods of drought. Growing drought-tolerant species is another option to cope with dry periods. Among others, cocksfoot (Dactylis glomerata L.) and tall fescue are promising species in this respect (Cougnon, Baert, & Reheul, 2014b; Pontes, Carriere, Andueza, Louault, & Soussana, 2007). Cougnon, Baert, van Waes, and Reheul (2014a) studied perennial ryegrass and tall fescue in Belgium, either in a single-species sward or mixed with white clover under a cutting regime. Over a period of 3 years following the year of establishment, pure swards of tall fescue out-yielded pure swards of perennial ryegrass by 23%; the difference between perennial ryegrass and tall fescue increased every year and during dry spells differences were as high as 50% (Cougnon, et al. 2014a). As the N-content of the two species was not signifi-cantly different, tall fescue showed a net higher N acquisition and utilization efficiency than perennial ryegrass. Disadvantages of the species, compared to perennial ryegrass, are the lower digestibility of the organic matter (up to 7%-units less according to Cougnon et al., 2014a), the slow establishment and the lower animal prefer-ence. There is breeding work being carried out that aims to
overcome these disadvantages. The difference in animal intake tends to become smaller when the forage is wilted and ensiled (Luten & Remmelink, 1984). The lower digestibility of the organic matter is less of a problem when farms are in need of rations with a high structural value or fibre content. The better performance of tall fescue in dry periods might be explained by its rooting system. Differences in root biomass, root distribution in the soil profile and dimensions of roots in a 3-year-old cut sward of F. arundinacea, Festuca pratensis L., Lolium perenne L. and Festulolium are presented in Cougnon et al. (2017).
According to Reheul et al. (2007) and Bommele (2007), the establishment of white clover was superior in grassland swards sown on arable land than in renewed grassland swards (Figure 3), most probably because of the high amounts of mineralized N released after cultivation of the old sward that might have given a competi-tive advantage to the grass component of the mixture. Over a period of 3 years (year of establishment not included), white clover DM in the total DM yield was twice as high in grassland installed on arable land compared with renewed grassland (mean values of four N rates: 0, 100, 300 and 400 kg/ha). All benefits started to decline after the third year of establishment. It is remarkable therefore that there are partly unexploited benefits that may be gained from using arable land for grass production provided the farmer has enough land or has access to enough land.
A ley-arable system offers the opportunity to sequester substan-tial amounts of soil organic carbon. Averaged over a period of 35 years, the annual C sequestration in a ley-arable system on a sandy loam soil in Belgium was approximately 400 kg C ha 1. At the end of the trial period of 35 years, the arable land contained approx-imately 30,000 kg C ha 1 and the permanent grassland 55,000 kg
C/ha; and the C content in the ley-arable farming system was nearly right in between these two figures (Information Sheet 398.21).
3.2
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Responsible N management in ley-arable
systems
Nitrogen dynamics in ley-arable systems and in crop rotations were modelled in Vertes and Mary (2007) and experimentally quantified in Nevens (2003), Vertes et al. (2007) and Bommele (2007), and more recently in Verloop (2013) and in Hansen and Eriksen (2016). Reported data apply both to sandy soils and to sandy loam soils in Belgium, France, the Netherlands and Denmark.
Large amounts of N become available after the ploughing-out of grassland, offering opportunities to save N in subsequent crops in the arable phase. However, if improperly managed, this nitrogen is prone to leaching (Hansen & Eriksen, 2016; Kayser et al., 2008). Nevens and Reheul (2002a) reported a nitrogen fertilizer replace-ment value (NFRV) of the ploughed-down grassland of about 250 kg/ha; about half of this becoming available in year 1 after ploughing the grassland, about one-third in year 2 and the remaining fraction in year 3.
From an analysis of the data of Nevens and Reheul (2002a) one can deduce a responsible N management in ley-arable farming. To obtain a yield of forage maize equal to a yield on permanent arable land dressed with 180 kg N ha 1one needs no N in year 1, 75 kg/
ha in year 2 and 180 kg/ha in year 3 after spring ploughing of tem-porary grassland (Table 1). It is obvious that ley-arable farming offers comparable DM yields with a higher N-content in the forage maize and with about 50% less input of fertilizer N (Table 1). The manage-ment of the grassland in the ley-arable system reported above was as follows: annual N fertilizer dressings of 240–350 kg N ha 1, rota-tionally stocking with heifers except for the first cut which was mown at the stage when DM yields were 3,000–5,000 kg/ha. As the N-export is larger under a cutting regime than under a grazing regime, a new trial was established to test the hypothesis that more
F I G U R E 3 Evolution over time of white clover content in harvested herbage of different types of grassland in a cutting management and with annual N-fertilization of 100 kg/ha. PA: permanent arable land; TA: new grassland installed in permanent arable land (PA) or land that was used as arable land for 3 years in a ley-arable rotation (3 years ley, 3 years arable); TG, PG: renewed grassland after ploughing down temporary (TG) or permanent (PG; 36 years old) grassland. PPG: the reference, i.e., undisturbed 36-year-old permanent grassland. New grassland was installed with a mixture of one diploid and one tetraploid variety (equal weights) of perennial ryegrass (40 kg/ha) and 4 kg/ha of a diploid variety of white clover
nitrogen becomes available to the arable crops in situations when temporary grassland is grazed in comparison with when it is cut. The grazed plots in this trial received annually 200 kg N ha 1, and the cut plots received 300 kg N ha 1. The swards contained white
clo-ver with an aclo-verage annual ground coclo-ver of 20%–30%. The hypothe-sis was not supported, as no significant differences in DM yield were recorded for forage maize grown after grazed or cut temporary grassland. To have a full harvest (i.e., a harvest that minimally equal-led the harvest obtained on permanent arable land, dressed with 150 kg N ha 1) no nitrogen was needed during the first year after ploughing, 60 kg N/ha during the second year and 90 kg N ha 1
during the third year after ploughing.
3.3
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Constraints in ley-arable farming
The ploughing-out of grassland presents a potential problem, often underestimated, of insect larvae pest damage, which can lead to sub-stantial loss of seedlings in the opening crop of ley-arable systems. The problem can be solved by the use of insecticides, but there is a need for other options. Ansari, Evans, and Butt (2009) and Campos-Herrera and Guttierrez (2009) reported the use of pathogenic strains of entomopathogenic nematodes and fungi for wireworm (Agriotes lineatus L.) control. The former concluded that the combined use of these biocontrol agents may prove synergistic in the control of wire-worms and may offer a chemical-free approach to control this pest. Crops that compensate for the loss of individual plants, e.g., because the survivors produce extra tillers (as in the case of forage grasses and cereals), can limit the damage. Candidate crops for this are annual ryegrass or early-maturing spring cereals with stiff straw. An extra advantage of spring cereals is the timely installation of a crucif-erous cover crop guaranteeing a good uptake of residual nitrogen. Kayser et al. (2008) ploughed up 9-year-old grassland swards in the spring at three locations in northern Germany and installed spring barley followed by yellow mustard (Sinapis alba L.) during year 1 and silage maize in year 2 to be compared with silage maize grown dur-ing the first 2 years. Compared with maize, the barley followed by a cover crop reduced the soil mineral nitrogen by about 50%. Schmeer (2012) used a spring cereal as break crop before re-installing grass-land and showed that this option reduced N-leaching by 40% com-pared with autumn ploughing.
3.4
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The role of plant breeding
Renewal of grassland swards offers the opportunity to take advan-tage of the progress made in plant breeding. However, the progress in productivity of grass and white clover (Trifolium repens L.) by breeding is much smaller than in arable crops. Chaves et al. (2009), analysing the Belgian official variety trials in the period of 1966– 2007, reported an annual genetic gain in DM yield during that period of about 0.3% for both Lolium perenne and Lolium multiflorum. These figures are close to those reported by Laidig et al. (2014) based on data from the German official variety trials in the period 1983–2012. McDonagh, McEvoy, O’Donovan, and Gilliland (2014), analysing data from the trials for the Recommended List in Northern Ireland in the period of 1972 up to 2012, reported annual DM yield genetic gains of 0.43% for Lolium perenne and 0.37% for Lolium multiflorum. The annual genetic progress in DM yield of white clover and red clover is similarly small (Annicchiarico, Barett, Brummer, Julier, & Marshall, 2014): about 0.5% per year. This means that in the short term, no spectacular yield advances are to be expected from the genetic pro-gress all the more because the capitalizing of the genetic gain owing to grass seems very inconsistent in practice (Laidig et al., 2014). In the absence of spectacular genetic gains, ley-arable farming offers remarkable opportunities.
4
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M E C H A N I Z A T I O N A N D
O R G A N I Z A T I O N O F H A R V E S T
As weather conditions in the Low Countries frequently are highly variable, the time of harvest can greatly influence the quality of the forage at the point of harvesting. Good weather forecasts together with a large capacity of harvesting machinery allow more efficient use of periods of good weather, thereby avoiding risks of quality losses due to bad weather conditions during harvesting. Harvesting large areas in a short period of time also allows the filling of bunker silos or the production of bales that are of uniform quality. The use of heavy machinery however, especially if operating during adverse conditions, can often be detrimental to soil structure and cause dam-age to the swards, and this in turn can lead to a decline in yield and the need for renovation measures.
T A B L E 1 Performance of forage maize grown in monoculture, either on permanent arable land or in ley-arable farming (3 years ley, 3 years arable) on a sandy loam soil in Belgium in the period 1990–1998. The figures in the table are the accumulated yields over 9 years, registered in three successive ley-arable cycles; relative values between brackets. Deduced from Nevens and Reheul (2002a)
Forage maize grown in monoculture, on permanent arable land fertilized with 180 kg N ha 1
Forage maize grown in ley-arable farming, with 0 N in year 1 after the
ploughing-out of temporary grassland, with 75 kg N ha 1in year 2 and with
180 kg N ha 1in year 3
DM yield (kg ha 1): 177,500 (100) 173,100 (98)
Applied N (kg ha 1): 1,620 (100) 765 (47)
kg DM (kg N applied) 1 109 (100) 226 (207)
A restricted survey in Belgium and the Netherlands (conducted by the authors of this article) among farmers and contractors who specialized in forage harvesting gave us information on the amounts and speed at which grass and forage maize currently can be har-vested and ensiled. Results depended heavily on the kind of machin-ery used, the field characteristics, on whether the work was performed by farmers or contractors, the number of working hours per day and the distance between field and farm. The provided data on grass are applicable to cuts of about 3–4 t/ha.
Farmers mow 2–3 ha/hr, contractors with the newest machinery up to 6–9 ha/hr, and whereas farmers can mow 20–30 ha/day, con-tractors can mow up to 60–90 ha/day. The time needed for spreading, raking and swathing the grass varies between 2 and 10 ha/hr: the large variation is due to the variation in numbers of rotors on the machinery. When forage is harvested, contractors remove forage from up to 80 ha/day when using self-propelled forage harvesters; when using self-loading wagons the rate varies between 25 and 60 ha/day. If fields are close to the farm, it is not the harvesting machinery that is the limiting factor but the capacity to load the silo properly. Baling the grass is slower than piling the forage in bunker silos, but it can be done by just one or two people. Bales can then be transported later to the farm. Contractors can easily bale and wrap 20 ha/day. Self-propelling forage maize harvesters work at a capacity of 1–1.5 ha/hr.
In summary, a timely organization and an efficient mechanization of the harvest is the“icing of the cake“ in the forage production: the final reward delivered by appropriate high-performing varieties, culti-vated and managed according to the best agricultural practices, is provided by a well-organized and efficient harvest, thus maximizing the net harvested produce from the field.
There may be an important drawback associated with this effi-cient way of harvesting, in terms of it having negative effects on the grassland fauna. If large areas of grass are harvested simultaneously, grassland birds may not be able to explore the heterogeneity of a grassland landscape to feed or nest, many nests may be destroyed in a single day or their chicks may be unable to escape in time. An agronomical highly efficient management may then be in conflict with the provision of ecosystem services from grassland that pro-mote a habitat for fauna and flora. In turn, this conflict may lead to the imposition of new restrictions on land use.
5
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C O N C L U S I O N
“Doing more with less” by exploiting new knowledge and new devel-opments is an important element of sustainable intensification. Growing the newest crop varieties in an appropriate setting with good agricultural management offers the opportunity to optimize crop yields in the Low Countries. A well-organized and mechanized harvesting maximizes the net harvested produce.
Natural and legal restrictions in recent years have reduced the yields of most forage crops. Plant breeding has been able to stop this decline in yield, through the large annual genetic progress in for-age maize. As genetic progress and the related improved
performance in yield potential have been much slower in grasses and clovers, good management is here a prerequisite for maintaining yields at high levels. Good permanent grassland should be main-tained properly in order that swards may be kept for as many years as possible. If it becomes necessary for grassland to be re-estab-lished, ley-arable systems (e.g., 3 years grass, 3 years arable) are a good farming practice. Installing new grassland on former arable land is a much better option than grass-to-grass reseeding: the develop-ment of white clover is substantially better as are yield performances in dry years. Soil organic matter in a ley-arable system is intermedi-ate between that of permanent grassland and arable land. Forage maize grown after ploughed-out grassland can be grown with half of the nitrogen compared with that of three consecutive years of for-age maize in arable land, and nitrogen concentration of the fodder is better. Results of long-term field trials have allowed us to develop a responsible management of nitrogen use after grassland ploughing which will much reduce nitrogen losses. Maize in a crop rotation is to be preferred over monocultures, as a rotation provides an insur-ance against the effects of low-yielding years and it improves yield stability. Avoiding late-maturing forage maize varieties followed by timely sown catch crops allows for a more environmentally accept-able forage production. High capacity mowers, tedders, rakes and forage harvesters allow the harvesting of large areas of fodder crops in a limited period of time, enabling advantage to be taken of good weather spells to maximize the harvesting of good-quality forage.
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How to cite this article: Reheul D, Cougnon M, Kayser M, et al. Sustainable intensification in the production of grass and forage crops in the Low Countries of north-west Europe. Grass Forage Sci. 2017;00:1–13.
