You can’t eat your mulch and have it too : cropping system design and tradeoffs around biomass use for Conservation Agriculture in Cameroon and Madagascar

K. Naudin

Research output: Thesisinternal PhD, WU

Abstract

Conservation agriculture is defined by three main principles: minimum soil   disturbance, permanent soil cover and crop rotations. CA is promoted as a   promising technology for Africa, but to date, only a small area under CA fully   complies with the above three principles. CA has both short and long term   effects on crop productivity and sustainability through the modification of various   agroecological functions. These functions are related to the quantity of crop and   cover crop biomass produced and kept as mulch. One of the main challenges in   designing CA for smallholder farming systems in developing countries is the   competing uses for biomass, in particular for feeding livestock. The main   difficulties are linking the efficiency of agroecological functions to varying   degrees of biomass export, and evaluating the performance of cropping   systems at farm level, which is where the decisions are made. In North   Cameroon the quantity of biomass produced in the field has been doubled by   associating a cover crop with a cereal crop. Part of the biomass was consumed   by cattle during the dry season but the quantity of mulch that remained on the   ground had a positive impact on the cotton water balance in the driest part of   North Cameroon. In the Lake Alaotra region of Madagascar, the soil cover in   rice fields under CA can vary, from 30% to 84% even in the same type of field   depending on the plant used as cover crop, the quantity of biomass produced   and management of the residues. The range is even greater when different   kinds of fields are taken into consideration. Of course, the different   agroecological functions can be fulfilled to a greater or lesser extent depending   on the amount of available biomass and the resulting soil cover. The   relationship between the quantity of biomass and soil cover has been calculated   for different kinds of residues. We used these relationships to explore the   variability of soil cover that could be generated in farmers’ fields, and to   estimate how much of the biomass could be removed to feed livestock while   leaving sufficient soil cover. Our results showed that under farmers’ conditions   in Madagascar, the production and conservation of biomass was not always   sufficient to fulfill all the agroecological functions of mulch. For example, partial   export of biomass to be used as forage might have no effect in terms of erosion   control but may considerably reduce the efficiency of physical weed control. As   the balance between the potential benefits of exporting biomass and the efficiency of agroecological functions varies depending on the constraints and   goals of each farm, we chose to analyze the potential benefits of exporting   aboveground biomass to feed cattle at farm level. To this end, we modeled   different size farms in Madagascar to investigate the relation between raising   dairy cows and efficient application of CA. Our aim was to explore trade-offs   and synergies between combinations of CA practices (i.e. different amounts of   biomass exported) and the size of dairy cow herds (varying biomass needs and   animal production). Changing the percentage of soil cover in CA plots did not   significantly modify total farm net income, as this was more influenced by the   characteristics of the milk market. Overall, CA systems can be beneficial for   dairy cow farmers thanks to the forage produced, although the milk market and   thus the value of biomass for forage, has a major influence on the way CA can   be implemented at field level. To explore the range of possible cropping   systems in a given biophysical situation, we created a tool named PRACT   (Prototyping rotation and association with cover crop and no till). We used this   tool to organize expert knowledge on crops and cover crops, biophysical   characteristics of fields and agronomic rules and to link them using Malagasy   conditions. PRACT generate a list of cropping systems, i.e. crops and cover   crops and their sequences over three years. These cropping systems are   characterized by their potential agroecological functions and crop production.   The cropping systems are first selected based on the biophysical requirements   of plants, plant compatibility and agronomic rules. But all the systems are not   suitable for every kind of farm. Consequently using PRACT outputs, a second   selection of cropping systems can be made based on the characteristics of the   cropping system, i.e. crop production and agroecological functions. In this way,   the selected cropping systems can be reduced to a number that can reasonably   be handled by technicians and farmers. Finally, we recommend a more rigorous   definition and characterization of treatments when comparing CA to   conventional systems to obtain a clearer view of the link between the impact of   CA, crop rotations and the level of biomass production.   Key words: conservation agriculture, cropping system design, optimization,   cover crops, cotton, rice, Cameroon, Madagascar  

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Giller, Ken, Promotor
  • Scopel, E., Co-promotor, External person
Award date21 Dec 2012
Place of PublicationS.l.
Print ISBNs9789461734341
Publication statusPublished - 2012

Keywords

  • conservation tillage
  • cropping systems
  • cover crops
  • mulching
  • rotations
  • madagascar

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