Recent progress in developing more P-efficient genotypes of soybean and common bean, with support from the CCRP, has created an excellent opportunity to improve legume production in developing regions. However, in order to realize the potential of this technology, we need to 1) continue the soybean breeding program in China and to begin a bean breeding program in Mozambique with specific focus on P efficiency, 2) we need a better understanding of how traits conferring P efficiency in legumes affect crop responses to other environmental factors, 3) we need to know how P efficient legumes will affect agroecosystem productivity and sustainability, and 4) we need to know how P efficient legumes affect the physical and economic well being of rural communities.
The most direct development need this project addresses is the need to identify, develop, and deploy more P efficient legumes in China and Mozambique. In the current CCRP project we have made excellent progress towards developing new commercial varieties of soybean with superior P efficiency for South China. Eight new varieties are now in the final stages of regional evaluation before official release. A number of other materials have been identified from a wide survey of soybean germplasm that are currently in crossing programs. We are learning more about the value of specific root traits for P efficiency and how they can be combined to achieve even greater P efficiency; this information is continually being incorporated in the crossing programs. In this renewal project selection of soybeans suited for Mozambique will also be initiated. The soybean breeding effort in South China has developed considerable momentum and a renewal of this project should yield significant returns in terms of new soybean cultivars and breeding lines. Mozambique currently has no legume breeding effort for soil adaptation, and this project would initiate one, beginning with P-efficient common bean genotypes identified in Latin America and other parts of Africa by Dr. Lynch and his collaborators in the USAID Bean/Cowpea CRSP and CIAT. To preserve local genetic resources and in consideration of local food preferences, P-efficient bean lines will be developed from the landraces and grain classes already important in Mozambique/Malawi/Tanzania. Dr. Roland Chirwa, CIAT bean breeder based in Malawi, will be an important collaborator for this effort. By continuing the successful soybean breeding program in China and launching a bean breeding program for P efficiency in Mozambique, this project will directly support the development and deployment of P-efficient legumes in the target regions.
Numerous traits have been associated with P efficiency in legumes, including mycorrhizal symbioses, root hairs, rhizosphere modification through secretion of organic acids, protons, and phosphatases, and modification of root architecture to optimize soil exploration. Our research has demonstrated the central importance of root morphology and architecture in conferring P efficiency in soybean and common bean. Our research has also shown that these traits may incur ecological tradeoffs in certain environments. 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. In such systems, genotypes with root systems that balance both deep and shallow soil exploration may be required. While researchers have made substantial progress in identifying P efficiency traits in recent years, very little is known about the potential tradeoffs of those traits in specific cropping systems. This information is critical in order for crop breeders to select genotypes with traits that improve P efficiency without incurring other agronomic liabilities. This project will directly address this need by evaluating ecological tradeoffs for root architectural and morphological traits in the specific contexts of South China and Mozambique.
Phosphorus-efficient legumes may affect the productivity of other components of the agroecosystem, and by affecting soil quality could change the long-term productivity of the agroecosystem. These processes need to be understood so that deployment of efficient genotypes benefits the overall production system without negative consequences. We anticipate that most of these effects will be positive. Greater production of legumes would increase biological nitrogen fixation, thereby enhancing soil fertility and the growth of nonleguminous crops grown as intercrops or rotations. Greater biomass production should result in improved soil fertility in the medium to long term, since organic matter is critically important for water retention, nutrient retention, and root growth, especially in weathered tropical soils. Greater production of legume biomass would also provide more crop residues for animal fodder. There is some concern that P-efficient crops would 'mine the soil' by extracting greater amounts of nutrients over time. Our preliminary research on this subject in the current CCRP project indicates that additional P removal in grain would be more than offset by reduced erosion on sloping sites and increased bioavailability of soil P. The use of more P-efficient crops would also provide more income and incentive for the application of fertility inputs by farm households. The interactions of P-efficient legumes with intercrops such as maize need to be understood, as positive interactions through for example biological nitrogen fixation may be offset by increased belowground competition for water and nutrients. This project would directly address these issues by evaluating the impact of P-efficient legume genotypes on intercrop competition and nutrient cycling in Mozambique and South China.
The impact of P-efficient legumes on the well-being of rural communities will depend on numerous local social, cultural, and economic factors. The availability of inputs, especially improved seed, seed sharing networks, access to markets, commodity subsidies and imports, food storage options and spoilage following harvest, dietary preferences, infant weaning practices, availability of fuel for cooking legumes, gender control of land and household finances, are all examples of local factors that can play critical roles in the adoption, utilization, and impact of new germplasm. These factors will be especially important for the introduction of soy as a human food in Africa. In our current CCRP project we have characterized some of these factors in South China- this project would directly address this need by both ex ante and ex post analyses of farm households in Mozambique.
A significant achievement of our current CCRP project is the development of Dr. Yan's group at South China Agricultural University as a world-class research and training facility for P efficiency in legumes. The numerous students trained in this facility will have lasting impact on Chinese agriculture well beyond the life of the CCRP project. A far greater training need exists in SubSaharan Africa, which has very few scientists with expertise in plant nutrition. NAROs in Eastern and Southern Africa have negligible expertise in this area, and training opportunities through regional universities are scant. The lack of expertise in plant nutrition is a serious failing since low soil fertility and low rates of fertilizer use are principal constraints to crop production throughout the region. This project would directly address this need by providing formal training in plant nutrition for 3 scientists from Mozambique, as well as numerous workshops and field days with Mozambican communities.
