Sieglinde S. Snapp

Nutrients in Agroecosystems: Rethinking the Management Paradigm

Agricultural intensification has greatly increased the productive capacity of agroecosystems, but has had unintended environmental consequences including degradation of soil and water resources, and alteration of biogeochemical cycles. Current nutrient management strategies aim to deliver soluble inorganic nutrients directly to crops and have uncoupled carbon, nitrogen, and phosphorus cycles in space and time. As a result, agricultural ecosystems are maintained in a state of nutrient saturation and are inherently leaky because chronic surplus additions of nitrogen and phosphorus are required to meet yield goals. Significant reductions of nutrient surpluses can only be achieved by managing a variety of intrinsic ecosystem processes at multiple scales to recouple elemental cycles. Rather than focusing solely on soluble, inorganic plant‐available pools, an ecosystem‐based approach would seek to optimize organic and mineral reservoirs with longer mean residence times that can be accessed through microbially and plant‐mediated processes. Strategic use of varied nutrient sources, including inorganic fertilizers, combined with increases in plant diversity aimed at expanding the functional roles of plants in agroecosystems will help restore desired agroecosystem functions. To develop crops that can thrive in this environment, selection of cultivars and their associated microorganisms that are able to access a range of nutrient pools will be critical. Integrated management of biogeochemical processes that regulate the cycling of nutrients and carbon combined with increased reservoirs more readily retained in the soil will greatly reduce the need for surplus nutrient additions in agriculture.

Biodiversity can support a greener revolution in Africa

The Asian green revolution trebled grain yields through agrochemical intensification of monocultures. Associated environmental costs have subsequently emerged. A rapidly changing world necessitates sustainability principles be developed to reinvent these technologies and test them at scale. The need is particularly urgent in Africa, where ecosystems are degrading and crop yields have stagnated. An unprecedented opportunity to reverse this trend is unfolding in Malawi, where a 90% subsidy has ensured access to fertilization and improved maize seed, with substantive gains in productivity for millions of farmers. To test if economic and ecological sustainability could be improved, we preformed manipulative experimentation with crop diversity in a countrywide trial (n = 991) and at adaptive, local scales through a decade of participatory research (n = 146). Spatial and temporal treatments compared monoculture maize with legume-diversified maize that included annual and semiperennial (SP) growth habits in temporal and spatial combinations, including rotation, SP rotation, intercrop, and SP intercrop systems. Modest fertilizer intensification doubled grain yield compared with monoculture maize. Biodiversity improved ecosystem function further: SP rotation systems at half-fertilizer rates produced equivalent quantities of grain, on a more stable basis (yield variability reduced from 22% to 13%) compared with monoculture. Across sites, profitability and farmer preference matched: SP rotations provided twofold superior returns, whereas diversification of maize with annual legumes provided more modest returns. In this study, we provide evidence that in Africa, crop diversification can be effective at a countrywide scale, and that shrubby, grain legumes can enhance environmental and food security.

Organic matter technologies for integrated nutrient management in smallholder cropping systems of southern Africa

Abstract One of the biggest challenges in the tropics is to develop organic matter technologies which are adopted by the farmers. Technologies must be effective within farmer resource constraints, increase food production, reduce risk and enhance the soil fertility. Results from on-farm participatory research were used to quantify the effects of agronomic practices on soil resources. Agricultural productivity is primarily nitrogen (N) limited throughout Malawi, and sub-humid Zimbabwe. Tightening economic constraints faced by farmers in the region have reduced inorganic fertilizer inputs and necessitate increased reliance on biologically-fixed N and N cycling. Three components of organic matter technology were evaluated: (1) the effects of residue quality; (2) the role of deep rooting systems; and (3) tradeoffs between legumes grown for grain versus soil regeneration. Perennial systems investigated include improved fallows, intercropping, and biomass transfer. Annual systems include intercrops and rotations of cereals with legumes. The most promising non-food legumes were Tephrosia and Sesbania. Interestingly, high quality residues of perennial legumes were most effective at supplying N in the short to medium term, whereas low quality residues immobilised N. Low quality residues were problematic for smallholder farmers who need immediately available N. Challenges to adoption of perennial system technologies include establishment costs, resource competition and delayed benefits. Farmer adoption of annual grain legumes is promoted by the simultaneous production of food; however, those species which have a high N harvest index add little to no net N to the soil. Species that combine some grain yield with high root and leaf biomass, thus a low N harvest offer a useful compromise of meeting farmer food security concerns and improving soil fertility. Promising genotypes include Arachis, Cajanus, Dolichos and Mucuna spp. On-farm N budgets indicate that legumes with high quality residues and deep root systems are effective ways at improving nutrient cycling. Areas of future research priority for smallholder farms in southern Africa were identified, including technologies which combine inorganic and organic fertilizer and improve legume growth and establishment on degraded soils.

Managing natural resources for sustainable livelihoods: uniting science and participation.

Foreword by Joachim Voss, Director General, International Center for Tropical Agriculture (CIAT) * Preface * Acknowledgements * Introduction: Uniting Science and Participation in the Process of Innovation - Research for Development * Navigating Complexity, Diversity and Dynamism: Reflections on Research for Natural Resource Management * Whose Research, Whose Agenda? * Scaling Up and Out * Transforming Institutions to Achieve Innovation in Research and Development * Principles for Good Practice in Participatory Research: Reflecting on Lessons from the Field * Participatory Research, Natural resource Management and Rural Transformation: More Lessons from the Field * Participation in Context: Whats Past, Whats Present, and Whats Next * Annexe1: Summaries of Case Studies * Index

Sustainable soil management options for Malawi: can smallholder farmers grow more legumes?

Sole-cropped, unfertilized maize is the dominant cropping system throughout southern Africa. Yields have become stagnant and legumes are frequently advocated as an affordable option for resource poor farmers, to enhance productivity. Farmer participatory research was employed to test legume intensification as a means to improve maize-based systems in Malawi. A range of options were evaluated, from grain/legume intercrops of long-duration pigeonpea (Cajanus cajan) and groundnut (Arachis hypogaea) rotated with maize (Zea mays), to a relay green manure system of maize with Tephrosia vogelii (Fishbean). Two years of on-farm experimentation indicated that under on-farm conditions legume-intensified systems produced residues that contained about 50 kg N/ha per year, two-fold higher than sole-cropped maize residues. Grain yields from legume-intensified systems were comparable to yields from continuous sole maize, even in a dry lakeshore ecology. These preliminary findings were linked to farmer assessment, where farmers participating in the trials expressed strong interest in the technologies. Yet the probability of adoption remains uncertain. Associated surveys outlined constraints and trade-offs underlying technology choice, information that is not usually considered in conjunction with on-farm trials. Although the legumes were highly productive, farmers expressed worries about the marginal loss of maize production. While the trial performance was similar across regions, differences in market condition, farm resources and household composition appears to stimulate different technology choices. Farmers weigh the benefits of weed suppression and potential cash earnings, against the costs of seed, problems of seed access, labor requirements and problems of grain market access and price. Surveyed farmers commonly manage residues by burning. Promotion and experimentation with more efficient use of legume residues may offer higher short-term impacts than efforts to promote adoption of another cash crop. Ultimately, adoption and soil fertility benefits may depend on market returns to legume production. This study documents the value of researchers and farmers partnering in evaluation of technologies, adoption constraints and competing technology choices.

PARTICIPATORY RESEARCH ON LEGUME DIVERSIFICATION WITH MALAWIAN SMALLHOLDER FARMERS FOR IMPROVED HUMAN NUTRITION AND SOIL FERTILITY

SUMMARY Legume species are uniquely suited to enhance soil productivity and provide nutrient-enriched grains and vegetables for limited-resource farmers. Yet substantial barriers to diversification with legumes exist, such as moderate yield potential and establishment costs, indicating the need for long-term engagement and farmer-centered research and extension. This review and in-depth analysis of a Malawian case study illustrates that farmer experimentation and adoption of legumes can be fostered among even the most resource-poor smallholders. Multi-educational activities and participatory research involving farmer research teams was carried out with 80 communities. Over five years more than 3000 farmers tested legumes and gained knowledge of legume contributions to child nutrition and soil productivity. The average area of expansion of legume systems was 862 m 2 in 2005; 772 m 2 for women and 956 m 2 for men indicating a gender dimension to legume adoption. Farmers chose edible legume intercrops such as pigeonpea and groundnut over the mucuna green manure system, particularly women farmers. Interestingly, expansion in area of doubled-up edible legumes (854 m2 in 2005) was practiced by more farmers, but was a smaller area than that of mucuna green manure system (1429 m 2 ). An information gap was discovered around the biological consequences of legume residue management. Education on the soil benefits of improved residue management and participatory methods of knowledge sharing were associated with enhanced labour investment; 72 % of farmers reported burying legume residues in 2005 compared to 15 % in 2000. Households reported feeding significantly more edible legumes to their children compared with control households. Participatory research that incorporated nutritional education fostered discussions within households and communities, the foundation for sustained adoption of legume-diversified systems.

Soil nutrient status of smallholder farms in Malawi

Abstract A soil sampling exercise was conducted throughout 60% of the smallholder farm sector of Malawi, a small country located at the base of the Great Rift Valley. Soil samples (1,130) were geo‐referenced and analyzed for pH, texture, soil organic carbon (C), phosphorus (P), zinc (Zn), potassium (K), and calcium (Ca) status. Descriptive statistics of soil characteristics were used to evaluate soil fertility for two agricultural districts in Northern Malawi, two agricultural districts in Central Malawi, and one agricultural district in Southern Malawi. Generally soils were loamy sands and moderately acid, with “low”; to “sufficient”; nutrient levels. Over three‐quarters of soils sampled had organic C levels which were greater than 0.8%. This indicated that organic C status was adequate in the main to maintain soil structure, although much reduced from the non‐cultivated state. The organic C data supported observations of widespread nitrogen (N) deficiency in Malawi. High spatial variability of P and Zn ...

Farming for Ecosystem Services: An Ecological Approach to Production Agriculture

A balanced assessment of ecosystem services provided by agriculture requires a systems-level socioecological understanding of related management practices at local to landscape scales. The results from 25 years of observation and experimentation at the Kellogg Biological Station long-term ecological research site reveal services that could be provided by intensive row-crop ecosystems. In addition to high yields, farms could be readily managed to contribute clean water, biocontrol and other biodiversity benefits, climate stabilization, and long-term soil fertility, thereby helping meet societys need for agriculture that is economically and environmentally sustainable. Midwest farmers—especially those with large farms—appear willing to adopt practices that deliver these services in exchange for payments scaled to management complexity and farmstead benefit. Surveyed citizens appear willing to pay farmers for the delivery of specific services, such as cleaner lakes. A new farming for services paradigm in US agriculture seems feasible and could be environmentally significant.

Farmer preferences and legume intensification for low nutrient environments

Improved varieties of legumes adapted to nutrient deficiency have the potential to improve food security for the poorest farmers. Tolerant varieties could be an inexpensive and biologically smart technology that improves soils while minimizing fertilizer costs. Yet other technologies that improve productivity and appear to be biologically sound have been rejected by farmers. To translate benefits to smallholder farmers, research on low-nutrient tolerant genes and crop improvement must keep farmer preferences and belief systems in the forefront. We review farmer participatory research on legume-intensification and soil fertility management options for smallholder farmers in Africa, including recent results from our work in Malawi and Kenya. We suggest that indeterminate, long-duration legumes are the best bet for producing high quality residues, compared to short-duration and determinate genotypes. This may be due to a long period of time to biologically fix nitrogen, acquire nutrients, photosynthesize and grain fill. Also, the indeterminate nature of long-duration varieties facilitates recovery from intermittent stresses such as drought or pest pressure. However, indeterminate growth habit is also associated with late maturity, moderate yield potential and high labour demand. These traits are not necessarily compatible with smallholder criteria for acceptable varieties. Malawi women farmers, for example, prioritized early maturity and low-labour requirement, as well as yield potential. To address complex farmer requirements, we suggest the purposeful combination of species with different growth habits; e.g. deep-rooted indeterminate long-duration pigeonpea interplanted with short-duration soyabean and groudnut varieties. On-farm trials in Malawi indicate that calorie production can be increased by 30% through pigeonpea-intensified systems. Farmers consistently indicate strong interest in these systems. In Kenya, a 55% yield increase was observed for a doubled-up pigeonpea system (a double row of pigeonpea intercropped with three maize rows) compared to traditional, low density intercrops. However, the need for improved pigeonpea varieties with high intercrop suitability, including reduced early branching, was highlighted by a farmer preference study in the same area. These examples illustrate the potential for participatory research methodologies to drive biophysical research in farmer-acceptable directions.

Use of N immobilization to tighten the N cycle in conventional agroecosystems.

Soils in conventional agroecosystems are purposely held in a nitrogen (N)-saturated state to maximize crop yields. Planting winter annual cover crops when fields are usually fallow has been proposed to ameliorate N losses from soils. In this study we introduced winter annual cover crops into an N rate study with plots fertilized at 0, 34, 67, 101, 134, 168, and 202 kg N/ha in maize (Zea mays L.) to determine how winter annual cover crops affect yields, N2O and NO3- fluxes, and N pools. At the six-leaf stage and during flowering, incorporation of cover crop into soil resulted in a 30% reduction in maize biomass. Three weeks after fertilization, KCl-extractable soil mineral N was 75-87% lower in covercropped soils than in no-cover soils, indicating that N had been immobilized in the covercropped soils. At physiological maturity, there was no difference between cover and no-cover treatments in crop yield, which was maximized at 9 Mg/ha in 2006 and 7 Mg/ha in 2007. Where N rates exceed crop requirements, cover crop incorporation may reduce N exports as NO3- and N2O. Tighter N cycling in conventional agroecosystems could be fostered by matching N rates to the amount of N removed with grain and using N immobilization to retain N and support yields. If N immobilization is viewed as a means for efficient fertilizer N use rather than a process that decreases crop productivity, growers might be more willing to adopt cover-cropping practices.