Conservation Agriculture Research Updates - August 2015

Due to the scarcity of alternative organic amendments, the retention of crop residue in fields can be considered key in promoting physical, chemical, and biological attributes of soil health in agricultural systems of developing countries. This article reviews crop residue management practices, mainly surface retention, incorporation or removal, describing their advantages and limitations in cereal-based agroecosystems in developing countries. They conclude that interventions such as intensification, partial retention, improved return of nutrients from manures, and the provision of substitutes to the current functions of livestock (e.g. mechanization, insurance) could reduce these residue trade-offs in favor of promoting long-term soil health.

This field study in Brazil was carried out to investigate the effects of cover crops in organic no-till vegetables systems on changes in soil organic matter and CO2 emissions, in the dry and rainy seasons. They conclude that The contribution of organic residues increases the water holding capacity and reduces soil temperature. No-till reduces soil disturbance and promotes a positive balance of C. Organic no-till vegetable systems is a strategy to increase soil C and should be encouraged in order to increase soil quality in the Atlantic Forest Biome in Brazil.

Present-day Indian farming systems are posing challenges to land, water, and the atmosphere, besides affecting biodiversity. With a view to sustainable development in Indian agriculture, CA is being promoted. Tillage is an integral component of traditional Indian agricultural systems with a view of controlling weeds. This paper suggests that an integrated management system encompassing a selection of appropriate crop cultivar and cropping system coupled with CA principles would aid in the management of weeds.

Earthworms and termites are important in ecosystem functions and so are important for sustainable intensification. Their role in agricultural management and CA are not well known. This study aimed to quantify soil macrofauna and its impact on soil aggregation, soil carbon and crop yields in a maize–soybean system under tropical sub-humid conditions in Western Kenya with tillage and residue retention. A macrofauna exclusion experiment was superimposed in 2005 through regular insecticide applications, The application of insecticides drastically reduced macrofauna populations. Macrofauna exclusion resulted in 34% higher maize grain yield and 22% higher soybean grain yield, indicating that pest damage – probably including termites – overruled any potentially beneficial impact of soil macrofauna.

No-till is an important way to control erosion in Brazil where it is practiced on about 30Mha.The objective of this study was to evaluate soil and surface runoff losses on small and large plots with differing slope lengths, cropping sequences and tillage systems in southern Brazil. This was a 14 year long term experiment on a well drained Oxisol. Results show that, when compared with conventional soil tillage soil losses for NT were > 70% lower. However, the benefit of reduced surface runoff losses was less evident suggesting the need to implement additional practices to control surface runoff.

In complex mixed crop-livestock systems with limited resources and biomass scarcity, crop residues play an important but increasingly contested role. This paper focuses on the farming systems in semi-arid areas of Zimbabwe. It quantifies the trade-offs and profitability of residue allocations and suggests alternative biomass production options.They conclude that further research is needed to establish the competitiveness of alternative biomass enhancing technologies and the socio-economic processes that can facilitate sustainable intensification of mixed crop-livestock systems in semi-arid environments.

Competition for crop residues and other organic resources leads to poor nutrient cycling in Kenya.This paper reviews whole farm nutrient cycling efficiencies to identify the most efficient farmer strategies considering labor and financial constraints.They conclude that efficient nutrient cycling for manure and improved cattle feeding are essential to increase use effiiciencies of any external nutrient added to these farms.

Crop residue mulch is essential for CA but this resource is important to feed animals in mixed crop-livestock systems. There is competing farm uses for this resource. This paper looks at the social and household level trade-offs for the residues in Mexico at the regional, community and household levels. In Mexico residues are important for animal feed and also income. Partial residue retention as mulch is discussed for CA. This issue remains a challenge for resource-poor farmers and needs more study.

There are many contested trade-offs concerning biomass resources such as feed, fuel, mulch, compost or the market. This paper summarizes yet a new body of evidence from 10 studies on trade-offs in the allocation of cereal crop residue biomass between soil management and livestock feeding in developing regions, published in the special issue of Agricultural Systems ‘Biomass use trade-offs in cereal cropping systems: Lessons and implications from the developing world’. The paper reflects on their main findings and methodological progress, and on the new and not-so-new implications of these findings for research and action in the development agenda.

Declining soil fertility in Zimbabwe is resulting in declining maize yields.This long term on-farm study tested the feasibility and viability of conservation agriculture (CA) systems under low fertility and erratic rainfall. CA seeding systems based on animal traction excelled and significantly increased maize productivity by up to 235% (1761 kg ha-1) and legume productivity by 173% (265 kg ha-1) as compared to the conventional control treatment. Soil quality indicators such as infiltration and soil carbon improved 64-96% and 29-97 %, respectively, over time. They conclude that successful CA promotion requires that the systems are adapted to farmers’ circumstances.

Cropping systems in the drylands of west Asia are characterized by grazing, burning or harvesting of stubbles, multiple cultivations and late sowing, which can limit yields and lead to soil erosion and degradation.This long term rainfed experiment at ICARDA compared tillage and no-tillage in combination with early and late sowing. The increased grain yields achieved in this study, in combination with lower costs and greater profits, suggest ZT plus early sowing should be evaluated and promoted more widely as an attractive cropping technology for farmers in the MiddleEast.

CA is promoted as a promising technology to stabilize and improve crop yields in Africa and Madagascar. But issues of retaining crop residue soil cover is difficult because of competing use of residues for animal feed. This paper uses an optimized model at the farm level to explore the trade-offs between CA and dairy cow herds in Madagascar. CA was not feasible for farms with no irrigated paddy fields or when forage fetched a high price regardless of the constraint for % of soil cover to be kept on CA fields. Overall, CA systems can be beneficial for dairy cow farmers due to the forage produced, although the milk market and thus the value of biomass for forage, has a strong influence on CA practice at field level.

The paper discusses strategies for reversing soil degradation by increasing research efforts to better understand the role of soil biology. It highlights what future needs are needed for issues that are not well understood and how soil biology can be manipulated to improve productivity and reverse degradation.

CA in Spain is gaining acceptance with 1.28Mha in 2013. This is partly due to institutional support from regional governments and rural development programs. This paper is a review of how CA has evolved in Spain over the past 10 years.

This paper discusses the disconnect between academic research and practical realities of farming and the way policies are developed. The paper explains the conclusions of a global meta-analysis in Nature that suggests CA and in particular zero-till produces lower yields as compared to conventional tillage. But the analysis uses no-till fields without mulch cover, an important component on the success of no-till.

Cereal residues are vital to feed livestock in the dry season in Africa. Yet they can also be important as mulch if left on the soil surface. This paper uses simulation models to simulate sorghum residue allocations at three scales - the plot, farm and territory. Plot scale suggests that without nitrogen, mulch has a positive effect on cotton yields when using small amounts. Greater amounts sequester nitrogen and reduce yields so addition of nitrogen is needed. At the farm scale the results are discussed in relation to number of farm animals owned. The paper then suggests optimum mulch allocations depending on number of animals owned. There is also discussion at the territory scale.