Global Issues Paddock Action. Proceedings of the 14th Australian Agronomy Conference. September 2008, Adelaide South Australia. © Australian Society of Agronomy www.agronomy.org.au. Edited by MJ Unkovich. Plant populations to improve yield of dryland maize in northwest NSW Sam Simons 1 , Daniel KY Tan 1 , Stephanie Belfield 2 and Bob Martin 3 1 Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Sydney, NSW 2006, Australia. www.usyd.edu.au Email d.tan@usyd.edu.au 2 New South Wales Department of Primary Industries, Moree NSW 2400. www.dpi.nsw.gov.au Email stephbelfield@bigpond.com 3 New South Wales Department of Primary Industries, Primary Industries Innovation Centre, Tamworth NSW 2340. www.dpi.nsw.gov.au Email marti27@une.edu.au Abstract Maize is a crop that can contribute to the increasing need for both feed grains and silage in Australia. Rain- fed maize production has attracted much attention among farmers in the more marginal cropping regions of Australia as an alternative to traditional summer crop options. However, the optimal row spacing for dryland maize systems in northern NSW is still uncertain. Maize hybrids (Maximus, Hycorn 424), plant population density (10, 20, 30 and 50,000 plants/ha) and row configuration (solid row, single skip and double skip row) were evaluated at Moree, northwest NSW during the summer of 2006/07. Yield performance of the shorter season hybrid, Maximus was superior to Hycorn 424, achieving optimal yield at 20-30,000 plants/ha while the longer season hybrid, Hycorn 424 performed best at 10–20,000 plants/ha. However, above ground dry weight of Hycorn 424 was greater than that of Maximus, being positively correlated with increasing plant density, while dry weight of Maximus remained relatively stable with increasing plant density. It is possible that earlier maturing hybrids are less affected by severe terminal drought stress for grain production while later maturing hybrids are better for forage production. Single skip configurations achieved maximum grain yields and harvest index. The grain yield and harvest index levels were extremely low as consistent with a severe terminal stress during a below average rainfall season. This study highlights the riskiness associated with growing dryland maize in northwest NSW. Key Words dryland maize; plant population; row configuration; yield; harvest index Introduction Maize can contribute significantly to the increasing demand for both feed grains and silage in Australia. However, maize production in areas of marginal rainfall (<600 mm annual rainfall) is considered less reliable than grain sorghum (Robertson et al. 2003). High intra-seasonal variation in timing and amount of rainfall received in these marginal areas means that water stress is a major production limitation. Thus, maize has not found widespread acceptance as it is considered one of the riskiest crops to grow by many farmers (Robertson et al. 2003). Widely accepted strategies among dryland farmers to manage risk include fallowing, cultivar selection, optimising plant population density and planting date (Birch et al. 2008). Quicker maturing maize may be better able to take advantage of a full profile of soil water and minimise the risk of running out of water before the crop matures while avoiding the peak summer heat at tasselling when planted in spring. Plant population density and row configuration are two important cultural management decisions that influence crop growth, resource availability and yield potential. Some overseas work has been conducted investigating dryland maize populations (Westgate et al. 1997; Johnson et al. 1998; Norwood 2001; Lyon et al., 2003). In Australia, there has been substantial work done on optimising density and row configuration in dryland cotton (Bange et al. 2005) and sorghum (Whish et al. 2005) but not in dryland maize (Birch et al. 2008). This paper evaluates the yield response of two maize cultivars differing in maturity (Maximus, Hycorn 424) growing in three row configurations (solid rows, single skip row, double skip row) in four plant population densities (1, 2, 3, 5 plants/m 2 ) under rain-fed conditions in Moree, northwest New South Wales (NSW) during the summer of 2006/07. Methods Treatments and experimental site The field experiment was conducted on a black vertosol at “Carossa” (29°5’S, 149°7’E) located approximately 25 km west of Moree in northwest NSW. The previous crop on the experimental site was wheat harvested in Dec 2005, and the stubble was burnt followed by a light cultivation. The maize was sown into soil with plant available water of approximately 80 mm on 1 Sep 2006, with 66 kg/ha N as urea and 40