Innovations in Dryland Systems: Conservation Agriculture for Sustainable Intensification.

Results from long term sustainability trials in the Central Highlands of Mexico show that, in environments with water availability as a limiting factor, farming systems based on the three principles of conservation agriculture (CA) – minimum soil disturbance, soil cover with crop residues and crop rotation – result in increased yield under rain fed (semi) arid conditions. The increased productivity can be attributed to improved soil physical conditions. Nevertheless, in order to further optimize the system potential second generation issues related to pest management and weed management have to be understood. Results will be presented from the long-term trials related to both pest and weed management comparing different management systems. Conservation agriculture (CA) provides a favorable habitat for beneficial soil-dwelling organisms which may provide improved pest control. To determine the effect of CA on generalist arthropod predators and pests, we assessed the ground-dwelling arthropod assemblage prior to crop planting and shortly after crop emergence. In maize, activity-density of generalist predators (excluding ants) was higher in conventional agriculture treatments than in CA treatments prior to crop planting (P = 0.03), but no significant differences were apparent in arthropod activity-densities at the treatment level at any other time. In multivariate analyses, the arthropod community was affected by tillage in maize at both sampling dates (P = 0.05), and by residue after crop emergence in wheat (P = 0.03). Spiders trended toward a greater association with no-till treatments in maize and treatments with residue retained in wheat. In wheat, predation (biological control potential) was significantly lower in conventional compared with CA treatments (P = 0.05). Our results indicate that the type and amount of residue that remains at the soil surface may influence arthropod community dynamics. When adopting CA, using tillage for weed control is no longer an option, and weed communities and growth dynamics will change compared to conventional tillage practices. Therefore it is likely that weed control under CA will also need to be adjusted. A literature review indicated that the principles of CA, particularly crop rotation and surface residue retention, are in themselves methods of weed control. The combined use of all three principles can offer disproportionate advantages, and weed problems are more likely to occur if only one CA practice is utilized. This was confirmed by weed counts in the long-term experiment in central Mexico. Grass weed populations were more than twice as high in conventional tillage with monoculture of wheat (Triticum aestivum L.) than with zero tillage with residue removal and wheat monoculture. They were further reduced to less than 10% of the conventional population by combining zero tillage with residue retention and crop rotation.