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Plant nutrition and soil fertility

Our research has concentrated on the physiology and function of micronutrient deficiencies, particularly boron, zinc and molybdenum, and their diagnosis and prediction in crops and soils.

This programme is an international endeavour with collaborative links in Bangladesh, Cambodia, China, Germany, Japan, Thailand, and the USA.  In Western Australia the plant nutrition and soil fertility research focuses on the GRDC-funded projects listed below:

  • Profitable and sustainable nutrient management in the WA grains industry
  • Boron risk mapping in WA wheatbelt soils
  • Development and evaluation of management options to treat subsoil acidity in the field
  • Improving farm to catchment nutrient management for a profitable and environmentally sustainable grains industry

Other research topics covered by the group are:

  • Wheat Sterility
  • Boron in Soils and Plants
  • Rice nutrition research in Cambodia
  • Adaption of rice roots to changing soil water regimes
  • Profitable and sustainable nutrient management in the WA grains industry

Grains Research and Development Corporation (GRDC), the Department of Agriculture Western Australia (DAWA), the University of Western Australia (UWA) and Murdoch University (MU) are joint investors in a 3-year project with the following aims:

That the GRDC and other research investors will have a clear understanding of the issues and priorities in nutrient management for the WA grains region, and the information needed to make sound investments in relevant RD&E; and Farmers and advisers will profit from understanding the impacts and possible management of non-uniform nutrient distribution within soil profiles, created either as a side-effect of the farming system or by direct fertiliser placement.

The project will follow two lines of work, each addressed in its own module: firstly to develop a clear overview of the nutrient management issues to be dealt with in the medium- to long- term; and secondly to undertake innovative research into the opportunities coming from manipulating the distribution of nutrients throughout the rooting zone of plants.

This detailed analysis will be synthesized into an overarching situation statement on nutrient management in the western grain region.

Boron risk mapping for the western Australian wheatbelt.

Boron (B) deficiency is less well studied in Australia than other micronutrients, but is of increasing interest in grain cropping regions because of on-going mining of soil B reserves, the rising grain yield of the most widespread crops and the increased prevalence of oilseeds and legumes that generally have greater B demands for growth than cereals. The aim of this work carried in collaboration with Dr Mike Wong, CSIRO Land and Water, was to develop a risk map for B deficiency in the grain cropping regions of Western Australia (WA), whilst avoiding the high costs associated with direct B measurements for an area as vast as the south-west of WA.

The study firstly determined relationships between 0.01 M CaCl2 extractable soil B levels and readily available data on soil properties and parent materials for Reference Soils of south west Australia and secondly assembled direct evidence of B deficiency risk from surveys of farmers’ crops and soils and from glasshouse experiments. Across 73 Reference soils, there was a positive relationship between 0.01 M CaCl2 extractable soil B levels and clay (r2 = 0.50) and pH (r2 = 0.43) in the surface horizon. Soils containing < 0.5 mg B/kg generally had < 5 % clay and pHCaCl2 < 5.5. Plant and soil analysis surveys in farmers’ fields revealed 10-20 % of fields had low B levels below tentative critical levels. In a glasshouse experiment, B response in oilseed rape was obtained in four sandy acid soils, all developed on sandstone parent materials. From this prior evidence of B deficiency, evidence layers for surface soil pH, sub-surface pH, surface clay level and geology were weighted and combined using the Dempster-Shafer weight of evidence model to map B deficiency risk. The weightings of evidence layers were revised to increase the correspondence between predicted areas of high risk and with field areas with measured low B or B deficiency from a validation data set. The model helps over come the high cost associated with direct B measurements for risk mapping. A similar approach may have value for mapping risk of other deficiencies of relevance to agriculture.

A project on "Causes of Wheat Sterility in sub-tropical Asia" was conducted collaboratively with CSIRO Division of Plant Industry, Chiang Mai University and scientists from Bangladesh, China, Nepal and Pakistan to find solutions to the puzzling phenomenon of sterility in sub-tropical wheat.

Boron in Soils and Plants

The first International Symposium on Boron in Soils and Plants was held in Chiang Mai, 7-11 September 1997. This Symposium critically reviewed the state-of-the-art with boron research in soils and plants. Authors from 18 countries presented papers. The second International Symposium on Boron in Soils and Plants was held in Bonn (2001) and the third is planned for Wuhan, China in September 2005.

From 1993, Dr Bell has collaborated with researchers in Cambodia on nutrient management for rice. Through this collaboration, three Cambodian staff have completed PhD degrees at Murdoch.

Adaption of rice roots to changing soil water regimes

In Asia, rice is the most important staple food but padi rice cultivation uses large volumes of fresh water. Rice has low water use efficiency due to losses by evaporation, leakage from the root zone and run-off. Water productivity in rice is three to four times lower than in all other cereals. Many national governments in Asia are concerned to reduce freshwater use in agriculture and in padi rice production in particular to free up water resources for other sectors. This has led to the initiation of research and development on water saving rice production systems over the last few years (Dittert et al., 2005). In China, the Ground Cover Rice Production System (GCRPS, also called Plastic Film Mulching) has been shown to use less water and decrease evaporative water loss from rice field compared to the flooded system traditionally used.

Rice roots have evolved to absorb water and nutrients from the flooded padi soils. They may not be well adapted to efficiently absorb water and nutrients under fluctuating water regimes or in water limited soils (Bell et al., 2001). Indeed a major reason why rainfed rice yields in Asia has lagged behind those in irrigated padi fields is due to difficulties of the rainfed rice in water and nutrient acquisition (Wade et al., 1999a, b).

We propose the need for a more thorough understanding of the function and adaptation of rice roots and of nutrient availability in wet soils to close the yield gap between traditional and saving water rice systems. Such understanding should focus on nutrient use and water use efficiency. The yield gap may result from among other causes, the poor morphological and physiological adaptation of rice roots to less water. The acquisition of more basic knowledge of rice root adaption and nutrient and water use efficiency will support the long term development of saving water rice production systems capable of closing the rice grain yield gap.