Nutrient Status 1 Tree leaves

By the end of the trial period, both nutrient regimes had brought nutrient concentrations in apple leaves up into the standard range, while leaf P and Mg concentrations had exceeded the standard range, as specified by Reuter and Robinson (1997). This can be attributed to the fact that these minerals were added to the soil and so were in an available form for uptake by the tree roots. In contrast, the concentrations of leaf N, K and Ca in ‘Lapin’ and K in ‘Sweetheart’ fell to within minimum ranges as defined by Reuter and Robinson (1997). As each of the cherry trials was conducted in a different orchard, with a different soil type, it is likely that both the fertility and general chemical characteristics of the soil had a considerable influence on leaf nutrient status. After treatment applications, the soil in the ‘Lapin’ orchard had low concentrations of mineral nutrients and a high soil pH, compared to that of the ‘Sweetheart’ orchard, relative to the baseline level. Since Hyland et al. (2005) and Lyle et al.

(2006) have shown that pH has a major influence on the availability of nutrients in the soil, perhaps the marginal level of N, K and Ca in ‘Lapin’ and K in ‘Sweetheart’ leaves that occurred in the present study could be attributed to the effects of a combination of these factors (soil fertility, chemical characteristics including soil pH and mineral nutrient concentrations).

Further, it is believed that the concentrations of leaf nutrients may not always reflect the correct nutritional status of trees due to nutrient dilution and diffusion that occurs, especially when trees have a large crown. This is confirmed by several studies that have demonstrated that the rapid growth of different types of natural vegetation in fertile soils causes nutrients in the plant tissues to diffuse and dilute, thereby reducing their concentration (Boyd and Hess, 1970, Harner and Harper, 1973, Auclair, 1977, El-Ghonemy et al., 1978, Williams et al., 1978).

6.5.3.2 The soil

The results of almost two years of apple trials show that there was a slight improvement in available levels of NO3--N, P, K, Mg, and total C and Zn in the soil, with biochar treatment.

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There are several possible reasons for this: firstly, biochar can change soil nutrient availability, especially that of P, by altering the pH of the soil (Warnock et al., 2010). This is supported by Major et al. (2009) who state that biochar additions affect nutrient availability and efficiency. Secondly, biochar also has the ability to decrease nutrient leaching. For example a study by Major et al. (2009) demonstrated that the addition of biochar decreased NH4+ leaching in the surface soil, and biochar derived from low nutrient timber improved the maintenance of N in soil. Furthermore, results indicated that the soil in the Lapin orchard was improved by the liberation of P, K, Exc. K and Ca in response to EM inoculation, and in both orchards by the release of Mg and Exc. Mg. EM inoculation also reduced the pH in the soil of both cherry orchards, which may have caused more nutrients to be released. Hyland et al.

(2005) and Lyle et al. (2006) mentioned that soil pH plays a major role both in the release and absorption of nutrients from the soil.

6.5.4

Conclusion

This series of trials demonstrate that orchard floor management can affect the degree of AMF colonisation more than the shift from one nutrient regime to another. The results also showed that EM inoculation can have both positive and negative effects on AMF colonisation, depending on soil type. Another important finding was that the adsorption of certain nutrients, especially P, is dependent upon their availability in optimal concentrations in the soil. Finally, cover crops constitute good orchard floor management for the development of good quality fruit flavour. Thus, AMF colonisation, in conjunction with limited P input from orchard management practices, can have the potential to be a useful agricultural tool for the development of high quality fruit flavour characteristics.

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"Chapter 7"

General Discussion

To retain high levels of productivity, conventional farming systems need to use increasing amounts of synthetic fertilisers and pesticides, yet there is an increasing awareness of the impact of conventional agriculture on soil biology and the importance of soil biology in maintaining soil health and crop productivity. While the benefits of organic soil amendments and bio-fertilisers have been highlighted by many studies, outcomes for plant growth are not necessarily predictable due to the wide range of products available, the interactions between organic amendments and bio-inoculants, and their interactions with different soil types. The objectives of the studies within this dissertation were to improve knowledge on the effects of organic nutrient regimes compared with conventional nutrient regimes on total plant growth. Pot grown sunflower plants were used as a model system to investigate the impact of different organic soil amendments (Chapter 3 - 5). The bio-inoculants studied included effective microbes (EM) and arbuscular mycorrhizal fungi (AMF). The impact of organic amendments, EM and orchard floor management on AMF colonisation was also examined in a 3-year study in commercial apple and cherry orchards (Chapter 6). Nutrient regime and inoculation with EM and AMF exerted a variety of effects on the growth and development of sunflower, AMF colonisation structures of sunflower, apple and cherry roots and on fruit flavour of cherry and apple fruits (See Table 7.1 to 7.4).