Plant Production & Protection Division - AGP
Crop and Grassland Service - AGPC

Genetic manipulation within cropping systems to enhance integrated nutrient management: 1. Phosphorus

Development objective:

To increase small farmer income and agricultural sustainability in poor rural areas by improving yields of grain legume and the productivity of legume-cereal systems under conditions of low soil fertility


Phosphorus (P) is the most limiting nutrient for grain-legume production in the tropics and subtropics. While P fertilization is an obvious solution, third-world farmers generally cannot afford to invest in fertilizing grain legumes. Phosphorus fertilization is inefficient in many tropical soils because of fixation into forms that are unavailable to plants. Therefore, application of processed mineral fertilizers or amendments cannot be relied upon by themselves reasonably to redress such nutrient deficiency, for economic, logistic and many other reasons.

Sustainability has become a major issue of global concern during this decade, since most of the modern technology that is used to improve crop production in developed countries is based on the intensive use of chemical inputs in agriculture, with resulting adverse effects on the environment. Grain legumes contribute to the sustainability of cropping systems through their ability for biological N2 fixation, a process which requires additional plant P in order to function. Perhaps most important, limitations resulting from lack of soil fertility are closely related to problems of environmental degradation. Subsistence farmers abandon exhausted lands and clear new, previously forested areas in search of transient soil fertility on the agricultural frontiers. This leads to deforestation, loss of biological diversity, climate change and severe soil degradation. Crop genotypes that use limiting nutrients more efficiently would improve and stabilize production in existing cropping areas.

Where it is possible to identify plant species or genotypes that can better dissolve P from sparingly soluble soil and fertilizer sources, it is also possible to improve levels of available P and thereby increase and maintain cropping system productivity and biological N2 fixation, with low strategic levels of P inputs. There are three broad categories of mechanisms by which plants can increase their access to native or applied soil P:

* through modification of soil exploration by roots;

* by improved interactions with soil micro-organisms (like arbuscular mycorrhizal fungi);

* by modifying the rhizosphere to increase the availability of nutrients.

Project efforts would therefore focus on root exudates that could mobilize less-soluble soil phosphorus resources (e.g. to permit the use of rock phosphates as phosphorus fertilizers), and the modification of root architecture and improved symbioses with mycorrhizas for better access to limited P resources.

Recent advances in the understanding of the genetic control of nutrient-acquisition mechanisms have opened up hitherto unrealized possibilities for the favourable genetic manipulation of these mechanisms. This could be done through improved plant-breeding procedures or through new opportunities unfolding in the field of molecular biology. These suggest possibilities for identifying and transferring genes controlling root behaviour and nutrient uptake processes between genotypes and even species. The implication is that there are novel opportunities for applying advances in molecular biology to tackle problems of integrated nutrient management of agricultural production systems in marginal soils.

Grain legume crops have been chosen as the focus for this work because of their importance in the diets of the world's poorest people and for their pivotal role in maintaining soil productivity, particularly in the low-fertility soils of the tropics and subtropics, through their ability to fix atmospheric nitrogen. The coordinated approach of physiological analysis, agronomic evaluation and molecular genetics, all within a broader context of genetic resources, will be model for research in other crops. The analytical techniques applied to the characterization and understanding of improved P uptake are state of the art and have not been applied in an integrated manner to any other crop plants. Although our immediate concern is production in a Third World context, root biology, rhizosphere modification and crop nutrient efficiency are important yet poorly understood elements of sustainable agriculture in both developing and developed countries.

We envisage a consortium approach with maximum comparative advantage, involving a number of specialized laboratories and institutes in the developed world and a group of IARCs with expertise in various components of this proposed research theme, as well as strong links to developing country national programmes in Africa, Asia and Latin America.

Target beneficiaries:

* resource-poor consumers of the tropics and subtropics who derive a substantial proportion of their dietary protein from vegetable sources;

* resource-poor farmers of the tropics and subtropics who cultivate largely infertile and weathered soils in grain legume-cereal production;

* plant, crop and soil scientists in developing countries with limited understanding of plant-soil interactions under P-limiting conditions.

Phase I Outputs:

* Understanding of the traits responsible for low P tolerance in grain legumes will be invaluable for directed breeding, conservation and use of crop genetic resources, genetic engineering and agronomic deployment of improved germplasm.

* More sustainable P-efficient legume-cereal systems identified through trial data on cropping systems incorporating outputs from linked studies on root morphology, rhizosphere modification and mycorrhizal fungi.

* Maximization of potential advantages from the mycorrhiza-crop symbiosis through understanding of mycorrhizal ecology in natural and cropping systems. This will be obtained through novel methodologies for identification of AM fungal species and strains, and improved inoculation techniques.

Anticipated impact:

* Identification of traits responsible for improved P-uptake efficiency will make possible efforts directed towards development of genetic resources appropriate for low P soils, leading to the adoption of crops adapted to infertile soils and improved legume production by poor farmers forced to cultivate marginal lands.

* Adoption of P-efficient crop genotypes and systems identified and developed through this project will improve and stabilize production in existing infertile cropping areas and reduce degradation caused by shifting cultivation.

* The proposed research in rhizosphere biochemistry, molecular biology, root biology, nutrient cycling, mycorrhizas and other dimensions of soil-plant interactions will generate fundamental new knowledge of basic processes in plant biology and application of molecular techniques. This will have strategic importance in understanding and improving crop adaptation to tropical soils throughout the world.

International collaborating partners:


  • AgResearch, New Zealand
  • CAMBIA, Canberra, Australia
  • CIAT, Colombia, Costa Rica, and Uganda
  • CSIRO, Div. Tropical Crops and Pastures, Brisbane, Australia
  • CSIRO Div. Plant Industry, Canberra, Australia
  • EMBRAPA, Brazil
  • Food and Agriculture Organization (FAO), Rome
  • Hokkaido National Experimental Station, Japan
  • ICRISAT, India and Niger
  • IFDC, International Fertilizer Development Center, Alabama, USA
  • International Institute of Atomic Energy (IAEA), Vienna
  • International Institute of Biotechnology, Canterbury, Great Britain
  • INRA, Institut National de Recherche du Agronomique, Dijon, France
  • IITA, Nigeria and Uganda
  • National Institute for Agro-Environmental Sciences, Tsukuba, Japan
  • Pennsylvania St. University, University Park, PA, USA
  • Rutherglen Research Institute, Victoria, Australia
  • Tokyo University, Japan
  • Universidad de Costa Rica
  • University of Hohenheim, Germany
  • USDA - Agricultural Research Service, Cornell NY, USA
  • National Agricultural Research System (NARS) cooperators:
  • Institut d'Economie Rurale, IER - Mali
  • Institut National de Recherches Agronomiques du Niger, INRAN - Niger
  • Institut National Pour lÕEtude et la Recherche Agronomiques, INERA - Zaire
  • Institute of Agricultural Research, IAR - Nigeria
  • Instituto Colombiano Agropecuaria, ICA - Colombia
  • Instituto de Ciencias y Tecnologias Agropecuaria y Forestal, ICTA - Guatemala
  • Instituto Nicaraguense de Tecnologia Agropecuaria, INTA - Nicaragua
  • Kawanda Agricultural Research Institute, Uganda
  • Kenya Agricultural Research Institute, KARI - Kenya
  • Namulonge Agricultural Research Institute, Uganda
  • Secretaria de Recursos Naturales, SRN - Honduras
  • Selian Research Institute, Arusha, Tanzania
  • University of Costa Rica, Centro Investigaciones Agricola, UCR-CIA


Subproject 1, Roots $2 506 292

Subproject 2, Exudates $3 452 943

Subproject 3, Cropping systems $3 242 900

Subproject 4, Mycorrhizas $1 471 885