Nitrogen fixation program report

• Rubber Research Institute of Malaysia, Malaysia

Pasture, grain and forage legumes can make substantial contributions to agriculture by fixing atmospheric nitrogen, thus removing the need for costly fertiliser inputs. In Asian countries other mechanisms of biological nitrogen fixation, including rice-associated micro-organisms, any be important. However, a lack of information on the nitrogen economies of the agricultural systems, and in particular the role that fixation plays in maintaining soil productivity and nitrogen status, limits their application.
This project seeks to develop and test new and more reliable techniques for measuring nitrogen fixation, to ensure maximum use and efficiency of legumes in various tropical cropping systems. Initially, it will concentrate on groundnuts and soybean as inter-row crops in those rubber-producing systems in Malaysia, i.e. where smallholdings of 10 ha or less account for about 60% of the country's rubber production. Rubber trees take 57 years to mature, during which smallholders need another sources of income, and inter-row cropping with either of these grain legumes could provide the solution.
Techniques involving 15N and specific translocate analysis appear to offer the greatest scope for reliable estimation of nitrogen fixation, and Australia has considerable expertise in these areas. Initially, much of the developmental work on methodology of 15N will be carried out at CSIRO, Canberra in co-operation with the Rubber Research Institute of Malaysia (DRRI). It will include adaptation of methods for applying 15N in tropical conditions, properties of suitable reference plants and alternative methods of sampling plant-available soil nitrogen, together with all aspects of 15N analysis.
Field experiments will take place at three sites in each country to ensure a range of environments. The Australian sites will be at Tamworth (irrigated subtropics), at Grafton (1500 mm annual precipitation rainfed subtropics, on soils of low nutrient status) and at Wollongbar (2000 mm annual precipitation rainfed subtropics, on acidic basalt soils of moderate nutrient status). Malaysia's three sites will be at the RRI Experiment Station, Sungei Buloh (uniform rainfall), at Bahau (34 months dry) and at Kelantan (monsoonal rainfall). These experiments will be conducted in 500 sq ft plots of immature rubber. They will investigate: how to apply 15N; how to sample available 15N: 14N ratios; whether the 15N technique can be used in Malaysian agriculture; and the effects of different rainfall patterns and soils.
Scientists in the team will maintain close collaboration with those in the related Project 8306, to ensure adequate legume nodulation.
Although the project is designed initially to develop ways of measuring nitrogen fixation in grain legumes in rubber plantations in Malaysia, the methods developed will find wide application in Asia and Africa in national research programs and also in other ACIAR projects. China and Thailand have already expressed interest, and will probably become involved at an early stage. Once suitable techniques have been developed and tested, other countries will be approached to join the project.