Introduction

1. Water in Primary Industries Improving productivity in rice systems with better layouts Sam North & Don Griffin NSW DPI, PO Box 736, Deniliquin, NSW, 2710 Phone: 03 5881 9926 Email: samuel.north@industry.nsw.gov.au • Introduction • In southern NSW, rice grown in contour basin irrigation systems dominates irrigated agricultural production. This is because the terrain is flat, soils are slowly permeable, returns to labour and capital are high, and production and economic risk is low (thanks to historically abundant irrigation water and grower ownership of processing and marketing). • However, recent drought and ongoing Murray-Darling Basin reform, together with declining terms of trade and the threat of climate change, means rice growers need to find ways of improving their profitability. A scoping study (North 2008) identified waterlogging as a key impediment to improvement and found research was needed to inform old (15+ yrs) and often unsupported recommendations and aid decision making. • Our objective was to find ways of improving the design of contour basin systems in southern NSW so that higher yields could be obtained from non-rice crops whilst reducing operating and environmental cost. • Methods and Results • Agronomic performance • Data from a pot trial, plus soil and water measurements in small plots and in farmers fields during irrigations, was used to assess the effect of ponding duration on wheat growth and on waterlogging duration and intensity. Our experiments showed • Wheat growth between heading and flowering was only reduced by waterlogging after gaseous oxygen had been depleted 36 hrs • Oxygen levels in the surface horizon of field soils fell whilst the soil was saturated following surface irrigation, and did not recover until the surface soil had drained/dried to field capacity (Figure 1) • The average time for rice soils to dry/drain to field capacity following the end of ponding equated to 63 hours in October. • Irrigation performance • Flow rate, water depth, soil moisture and wetting front advance data was collected during 13 irrigations in 6 different basin configurations. • Irrigation opportunity times were found to be 40 to 50 hours in commonly occurring contour basin systems (i.e. lasered, parallel contour systems with bankless channel supply/drain) • This was greater than what most irrigators believed and was due entirely to slow drainage rates. Drainage times in these layouts, with commonly occurring slopes, were generally 4 times longer than fill times (Figure 2). • Operational performance • Subjective information on yields and maintenance costs was collected from farmers. Objective data on machinery efficiency was collected using GPS trackers placed on machinery during paddock operations. • Operational savings (labour and inputs) for all machinery operations are possible if overlaps can be eliminated (Table 1). Potential cost savings in the order of $15-$20 per ha per year were identified. • Conclusions • Based on our soil measurements, we calculated a maximum design opportunity time to ensure the risk of waterlogging is minimised, thereby increasing cropping flexibility and water productivity. • For most rice soils, this was determined to be 10 hours. • For sodic soils, it was found that frequent irrigations would likely result in waterlogging stress in non-rice crops, no matter how short the opportunity time. • Slow drainage NOT slow watering, was considered the major impediment to improved irrigation efficiency and water productivity. • The principle cause of long drainage times was the hydraulic connection between bays created by the bankless channel (Figure 3). • There is potential for considerable operational savings to be made with every machinery operation carried out in contour basin systems. By reducing the amount of overlap, the following savings in time, fuel, fertiliser, seed and herbicides are possible: • 10-15% by adopting GPS steering guidance • 10-40% by squaring up bays and making banks parallel • 30-60% if natural contour systems are converted to parallel contour, drive-over-bank systems (Kooloos & North 2007) and GPS guidance is adopted • Recommendations 1. Maximum irrigation opportunity time • Basin systems in the southern Murray-Darling Basin should be designed to ensure they can be watered and drained within 10 hours. 2. Supply infrastructure • Layouts should be evaluated prior to new works being done. Simple tools for measuring the depth and duration of ponding in bays exists. • If opportunity times are > 10 hours in bankless channel layouts, then they should be modified so that each bay is individually supplied. 3. Bay size and shape Layouts should be designed with banks that are parallel and a multiple of the machinery operating width apart. Further operational savings are possible with a move to drive-over-banks and the adoption of GPS steering guidance. Figure 1. Irrigation depth & rainfall (top); matric & redox potential (bottom) in top 5 cm of a RBE Figure 2. Cumulative applied volume (top) & ponded water depth (bottom) in 4 bays during an irrigation of a contour basin layout Table 1. Summary of GPS track data from machinery during paddock operations References Kooloos H., & North, S.H. (2007). The new “V-bay” flexible layout. 2007 Grains Research Update for Irrigation Croppers. Barooga, NSW, 2 August 2007. North S. H. (2008). A review of basin (contour) irrigation systems. 1: Current design and management practices in the Southern Murray-Darling Basin, Australia. CRC for Irrigation Futures Irrigation Matters Series No. 01-1/08. Figure 3. Irrigation of a contour basin using a bankless channel. This photograph shows how water filling the basin being irrigated has backed water up through the inlet structure (below the frame) and occluded drainage from the upstream bay. NSW Department of Primary Industries Agricultural Research & Advisory Station DENILIQUIN 2710