Food legumes have a unique potential to improve both human nutrition and agricultural sustainability; they provide a high-quality source of nutrients, N inputs through biological nitrogen fixation, and are considered a high-value crop for marketing. However, their potential frequently goes unrealized in some of the poorest regions of the world, where the predominance of highly weathered tropical soils constrains legume productivity. Most legumes perform poorly under low fertility conditions, especially where acid soil conditions cause free iron (Fe) and aluminum (Al) oxides to bind soil phosphorus (P) into forms unavailable to plants. Legumes are especially sensitive to low P availability since biological nitrogen fixation has a high P requirement. Application of P fertilizer is only a partial solution since P fertilizers are resource-dependent and expensive, and subject to the same chemical processes that immobilize native soil P. Besides phosphorus, nitrogen could be another important limiting factor for soybean growth due to the lack of effectively native rhizobial strains in most tropical and subtropical areas. Application of N fertilizer not only wastes resources but also causes environmental pollution.There has been significant progress in genetic improvement of common beans (Phaseolus vulgaris) and soybeans (Glycine max) for better adaptation to low soil P. Research at both Penn State University (PSU) and South China Agricultural University (SCAU) has demonstrated the central importance of root morphology (esp. root hair characteristics) and architecture in conferring P-efficiency in common bean. These root traits have been used at SCAU to screen for P-efficiency among soybean landraces and bred lines, as well as create new genotypes with improved P efficiency and enhanced nitrogen fixing capacity.The current project represents the second phase of an earlier CCRP project (2002-2005), which targeted the development of P-efficient soybean varieties P-deficient soils of South China. During phase one, collaborators at SCAU and PSU validated that the same traits that are important for P-efficiency in common bean are also important in soybean. The team also developed new P-efficient soybean varieties for the low P soils of South China, some of which have been commercially released to farmers in South China. These new genotypes have shown substantial yield gains in low P soil compared with conventional genotypes, in some trials doubling yield without additional inputs, thereby demonstrating the potential of this approach.During phase two, collaborators from Mozambique have joined the research team and the project’s mandate area have been expanded to include this southern African country where more P-efficient soybean and bean varieties could help to improve the health and well-being of some of the world’s most economically disadvantaged rural communities. Evaluating legume performance under Mozambique conditions will also be important for looking more closely at potentially important genotype-by-environment interactions for P-efficient root traits. For example, shallow-rooted genotypes are able to acquire more P from the soil since in most soils P availability is greatest in the topsoil and declines with depth. However, shallow-rooted genotypes are more sensitive to drought, which is also an important constraint in many agroecosystems, especially those in Southern Africa. In such systems, genotypes with root systems that balance both deep and shallow soil exploration may be required. This project are currently evaluating ecological tradeoffs for root architectural and morphological traits in the specific contexts of South China and Mozambique.Phosphorus-efficient soybeans and beans are likely to be extremely useful in the low fertility soils of South China and Mozambique. In order to realize the potential of this technology, Phase 2 of the project is focusing on the following activities: (1) continue the soybean breeding program in China and begin a bean and/or soybean breeding program in Mozambique with specific focus on P efficiency, (2) develop a better understanding of how traits conferring P efficiency in legumes affect crop responses to other environmental factors, (3) determine how P efficient legumes will affect agroecosystem productivity and sustainability, as well as the economic well being of rural communities, and (4) develop African scientific capacity in plant nutrition so that this effort can be sustained.
The overall goal of the project is to improve food security and agroecosystems sustainability in tropical-subtropical regions of China and Africa through increased productivity of soybean and common bean on low P soils.
Outputs and Outcomes:
Grain legumes play a key role in the food security of developing countries because of their unique importance to human nutrition and agricultural sustainability. Low soil fertility, particularly low phosphorus (P) availability, is the primary limiting factor to legume production in many of the developing countries. The CCRP project on legume adaptation to marginal soils, led by Xiaolong Yan at South China Agricultural University, addresses this problem by breeding and deployment of more P-efficient soybean and common bean that yield better than conventional cultivars in low-P soils, thereby improving the health, income, and productivity of rural communities.In the first phase of project (2002-2005), the team developed improved soybean germplasm with superior root characteristics that enable better adaptation to low-P conditions and more efficient utilization of applied fertilizers. After an integrated effort over four years, the team has gained insights into the physiological, genetic and molecular basis of P efficiency and the agroecological dimensions of efficient P utilization in the soybean production system, while at the same time developing a number of P efficient soybean genotypes that have passed the Chinese national regional variety trials. These improved soybeans have been released to farmers in South China. These new genotypes show substantial yield gains in low P soils compared with conventional genotypes, indicating a great potential for future impacts. Continued efforts are being made to realize the long-term objective of the project in developing new germplasm and technical innovations that may have great impacts on food security both in China and other developing nations, particularly in Africa.For the second phase of the project (2006-2009), a new partnership has been formed for an extended effort in increasing P efficiency and production of grain legumes in China and Africa. In the new phase, the project team has included partners in Mozambique while maintaining core activities in South China. The team continues to breed soybean for P efficiency and other important agronomic traits with the existing materials that we have developed and test the newly developed genotypes (varieties) under various soil/climatic conditions through Chinese National Field Trials. Cropping systems are being optimized (using intercropping, rotation, etc) through large-scale experimentation and farmer participatory research. The project is creating effective and reliable legume (particularly soybean) processing facilities that can be used in households of the rural areas. These research outcomes will not only generate great impacts in South China but will also serve as the technical reserve for generating impacts in Africa through training and collaborative research proposed for the second phase of the project. Project collaborators in Mozambique have launched a breeding program for more P efficient common beans and/or soybean, and are rigorously assessing the biophysical and socioeconomic impacts of P-efficient legumes on rural communities in Africa.