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To investigate the use of perennial legumes as a means of controlling and reducing water tables in pasture/crop rotations

Cocks, P.S. Professor; Ph: (08) 9380 2555; Fax: (08) 9380 1108; pcocks@agric.uwa.edu.au

Auricht, G. Mr; Ph: (08) 8303 9498; Fax: (08) 8303 9607; auricht.geoff@pi.sa.gov.au

Latta, R. Mr; Ph: (08) 9821 1755; Fax: (08) 9821 1127; rlatta@agkat.agric.gov.au

Fillery, I.R. Dr; Ph: (08) 9387 0681; Fax: (08) 9387 8991; i.fillery@ccmar.csiro.au

Research organisations: Faculty of Agriculture, University of Western Australia, Nedlands WA 6907; South Australian Research and Development Institute, GPO Box 1671, Adelaide SA 5001; Agriculture Western Australia, Katanning WA 6317; CSIRO, PMB, Wembley WA 6014

Sponsor: GRDC, Grains Research and Development Corporation

Objectives:

1. To develop perennial legumes that persist and spontaneously regenerate in crop/pasture rotation and, through summer growth and deep-rootedness, reduce water tables;

2. To devise establishment and management systems that make perennial legumes in general, and lucerne in particular, easier to manage, to study their effect on wheat yield and quality, and to determine their role in manipulating weeds;

3. To measure nitrogen fixation, nitrogen cycling and water use in perennial legume-based systems.

Methodology:

The research will focus on three main areas:

1. Germplasm improvement;

2. Improved management systems, and

3. The effect of perennial legumes on water tables, nitrogen economy and crop yields.

Germplasm Improvement: The fate of seeds produced by selected accessions of lucerne and other genera will be monitored in the soil. Regeneration will be determined each year in the presence and absence of parent plants, and in rotation with cereals. The effects of seed size, flowering and maturity time, and the presence of diseases and insects on seedling survival will be monitored.

Improved Management Systems: Best and cheapest methods for establishing existing perennial legumes will be explored. Autumn versus spring and under-sown with cereal versus not under-sown will be compared. The effect of grazing on plant survival will be studied, and the longevity of plants in different soil and climatic conditions will be compared.

Effect of perennial legumes on water tables, nitrogen economy and crop yields: Crop production and grain quality after pure and mixed stands of perennial legumes will be managed and water use estimated with a neutron probe. Evaporation will be measured by micro-meteorological means and infiltration by time domain reflectometry. Nitrogen fixation will be estimated using sup15 N natural abundance techniques. Root length, nitrogen profiles and mineralisation of soil organic matter will also be measured.

Progress:

Improved Management Systems:

There is a perceived need by the agricultural and land protection community to establish perennial plants over millions of hectares of arable WA. Successful and cheap establishment techniques are considered the major constraint in lucerne fulfilling the major component of that role. To successfully establish lucerne in conjunction with an annual field cereal has been considered important to provide an economic return in the initial year to allay some of the establishment costs. However, most importantly, variables such as weeds, insects and soil type must not be limiting factors.

Studies over 4 years 1995 to 1998 through the low and medium rain belts (300 to 450mm) have identified annual plants competing for sunlight and water as being the major limitation to successful establishment. As annual plant densities increase, establishing lucerne plant densities and vigour decreases. The seasonal rain determines the annual plant density that allows successful lucerne establishment.

The success of growing a field crop over an establishing lucerne becomes a risk management decision. It is based on a calculation between expected annual rain and the ability to achieve an economic crop return from an acceptable crop density. The field crop species needs to be taken into account in terms of its canopy cover and maturity length due to water use through the period of water deficit during the spring period. The ability to control volunteer weeds must also be included in the annual plant density calculations.

The effect of perennial legumes on water tables, nitrogen economy and crop yields:

Rotation studies to determine the comparative performance of a lucerne and an improved annual legume pasture in a pasture crop rotation have been carried out over 4 years, 1995 to 1998. Measurements have been made of annual pasture production, stored soil water, soil N accumulation and subsequent grain yield and quality over a pasture, pasture, pasture, crop rotation.

To date the studies have shown similar total annual biomass production between annuals and perennials, with the lucerne producing an increased proportion of the annual production through the "dry" period of the year. Nitrogen accumulation was similar between the species in line with the comparable biomass production. Lucerne reduced the stored soil water at both sites (medium and low rain zones) from a period 12 months following establishment until it was removed in preparation for the cereal crop in the 4th year of the study. Grain yields were similar in response to the two legume treatments. The studies will continue through an ongoing cropping phase to determine any variations in subsequent crop phases.

Period: starting date 1995-01; completion date 2000-12

Status: ongoing

Keywords: perennial legumes, lucerne, water tables, nitrogen cycling

Publications:

 Latta, R.A. and Blacklow, L.J. (1998). Comparative pasture growth and soil profile dryness of a lucerne and an annual legume pasture. Proceedings of the 9th Australian Agronomy Conference, Wagga Wagga, July 1998.

 

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