The PRACT tool (Prototyping Rotation and Association with Cover crop and no Till)

We identified six different kinds of information that can support the design of new CA cropping systems: i) crop adaptation to biophysical conditions, ii) cover crop adaptation to biophysical conditions, iii) agroecological functions of cover

crops, iv) crop production, v) compatibility for intercropping of crops and cover crops, and vi) agroecological functions of the overall cropping system. In PRACT this information is organized in a knowledge database including data on crops, cover crops, agronomic units, and the relationships between these three components (Fig. 5.1). The underlying expert knowledge had been developed since the 1990s in Madagascar and other tropical countries by a team of CIRAD agronomists and their local colleagues (Seguy et al., 2012) The expert knowledge was already formalized in technical manuals (Husson et al., 2009, 2012). PRACT allows the user to generate crop rotations based on CA principles for a defined agro-climatic context that are best adapted to cope with local constraints. It has been developed with the database management system MicrosoftAccess 2007^® to make it accessible for potential users in developing countries.

Figure 5.2. Simplified plan of information processing in PRACT, interactions with the user and output.

PRACT a tool for designing Conservation Agriculture systems

99 5.2.1 Tool development

PRACT is organized (Fig. 5.1) around a database with 28 plants which are crops, cover crops, or both, suited to the Lake Alaotra region of Madagascar:

Arachis hypogaea, Arachis pintoï, Arachis repens, Avena sativa, Brachiaria brizantha, Brachiaria ruziziensis, Cajanus cajan, Crotalaria grahamiana, Crotalaria juncea, Crotalaria spectabilis, Dolichos lablab, Eleusine coracana, Glycine max, Ipomoea batatas, Lolium multiflorum, Manihot esculenta, Mucuna pruriens, Oryza sativa, Pennisetum clandestinum, Phaseolus vulgaris, Solanum tuberosum, Sorghum bicolor, Stylosanthes guianensis, Vicia villosa, Vigna subterranea, Vigna umbellata, Vigna unguiculata, Zea mays. The plants are characterized according to their ability to be grown in different environments, here defined as agronomic units, a corpus of “rules” that specify the place each plant can have in intercrop associations or crop sequences, and their potential efficiency in fulfilling agroecological functions and characteristics such as

“simplicity of management” or “ability to produce during marginal periods” (Tab.

5.1).

The final output of PRACT is a list of cropping systems, i.e. crop and cover crop intercropping in the cropping season and in the off-season over a three year period. Each of the cropping systems is characterized by the same factors as the plants (Tab. 5.1). The characterization of cropping systems is calculated by summing up the characteristics value of each plant in the cropping system.

Even after applying filters, the number of possible cropping systems can be too large to be handled by technicians or farmers. Thus, a further step is to select from among these cropping systems those that fit in with farmers’ particular goals and constraints. Selection can be based on characterization of the agroecological function, or ease of implementation, or the species of crop and cover crop chosen by the farmer. The number of cropping systems can also be reduced beforehand, during the PRACT cropping system generation process, by selecting only some of the crops and cover crops based on farmers’

preferences. But reducing a priori the number of crops and cover crops will reduce the chances of identifying an innovative cropping system. We thus

propose that PRACT should be used in two steps: first obtain a list of possible cropping systems based on the local conditions and general agronomic rules;

and secondly choose from these systems those which fit in with farmers’ main goals and constraints for both crop and animal production.

5.2.2 Plant characteristics

Plants (crop and cover crop species) are characterized by their outputs (grain production, tuber/root production, and biomass/forage production) and qualitative impacts on agroecological functions. Both are translated into semi-quantitative indicators (Tab. 5.1). All these indicators are based on expert knowledge (Husson et al., 2009).

Table 5.1. Characteristics and agroecological functions of crops and cover crops in the PRACT database.

SOM

PRACT a tool for designing Conservation Agriculture systems

101 5.2.3 Agronomic units

Agronomic units are defined as areas which provide uniform biophysical conditions that impact plants and cropping systems. Therefore a different set of cropping systems can be selected for each agronomic unit. For Lake Alaotra in Madagascar each of the 17 agronomic units is discriminated by: i) the position in the toposequence, ii) soil fertility and compaction, iii) the drainage or water logging status, iv) potential for irrigation management, v) the possibility or not of supporting the growth of an off-season cover crop (Fig 5.2, Fig. 5.3, Husson et al. 2012).

Figure 5.2. Locations of the main agronomic units along the toposequence in the Lake Alaotra region, adapted from Husson et al. (2012).

Figure 5.3. Decision tree to select the type of agronomic units in the lake Alaotra region as a function of the position in the toposequence, risk of flooding, soil compaction and possible off-season cropping due to the presence of a ground water table, adapted from Husson et al. (2012).

5.2.4 Agronomic rules

Plant species are also characterized by three kinds of constraints: i) whether or not plants can be grown on the different agronomic units, ii) whether or not the plants can be intercropped or grown in sequence, iii) more elaborate rules regarding plant associations and successions. The constraints are applied in three sequential steps in the cropping design process. The first step is the compatibility of plants and the agronomic units. It is determined with regard to each plant’s requirements in terms of soil and the water regime. Soil is considered in terms of compaction and fertility. The water regime during the rainy season is driven by drainage and irrigation. Drainage is mainly determined

PRACT a tool for designing Conservation Agriculture systems

103 by the position in the toposequence. Three types of water supply were identified: strictly rainfed fields, fields irrigated from channels only in the event of sufficient rainfall, or fields irrigated from channels with a secure access to water throughout the cycle (coming from a dam or a permanent source). During the dry off-season no fields can be irrigated and the only water source for crops and cover crops is capillary rise. The second constraint applied is to determine compatibility between crops and cover crops for intercropping. The possibility of associating plants results mainly from potential competition for light, water and/or nutrients. Table 5.2 lists crops and cover crops which can or cannot be intercropped together.

Table 5.2. Possibilities for intercropping (Y) or not (N) between crops and cover crops as given in the PRACT database.

The third step uses more elaborate rules about the crop sequences which are defined for each agronomic unit in PRACT. Below we describe how six groups

Arachis pintoï Arachis repens Avena sativa Brachiaria brizantha Brachiaria ruziziensis Cajanus cajan Crotalaria grahamiana Crotalaria juncea Crotalaria spectabilis Cynodon dactylon Dolichos lablab Eleusine coracana Lolium multiflorum Mucuna pruriens Pennisetum clandestinum Stylosanthes guianensis Vicia villosa Vigna unguiculata

Arachis hypogaea N N Y Y Y Y Y Y Y Y N Y Y N Y Y Y N

Vegetable N N Y N N Y Y Y Y N N Y N N N Y Y N

Glycine max N N Y Y Y N N N N Y N Y Y N Y Y Y N

Manihot esculenta N N Y Y Y Y Y Y Y Y N Y Y N Y Y Y Y

Ipomoea batatas N N Y N N N N N N N N N N N N Y Y N

Oryza sativa Y Y N N N N N N N N N N N N N Y Y N

Phaseolus vulgaris N N Y Y Y N N N N Y N Y Y N N Y Y N

Solanum tuberosum N N Y N N N N N N N N Y Y N Y Y Y N

Sorghum bicolor Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y

Vigna subterranea N N Y N N Y Y Y Y N N Y N N N Y Y N

Vigna umbellata N N Y N N N N N N N N Y N N N Y Y N

Vigna unguiculata N N Y N N N N N N N N Y N N N Y Y N

Zea Mays Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y

of rules are defined for specific agronomic units of the Alaotra Region, but these are generic rules which can be applied to similar locations elsewhere.

Rule 1: if a cover crop is grown in the rainy season in Year n then the same