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Title: Maintaining profitability and soil quality in cotton farming systems
Authors: Hulugalle, Nilantha
Keywords: rotation crops
stubble management
irrigated and dryland Vertosols
Soil physical and chemical properties
soil health
Economic returns
Spatial and temporal deep drainage
problems with retaining crop stubble
stubble incorporation
Issue Date: 30-Jun-2005
Publisher: NSW Department of Primary Industries
Series/Report no.: ;CRC45C
Abstract: The effects of rotation crops and stubble management (including the residual effects of past rotation crops) on soil quality, carbon sequestration, deep drainage, nutrient leaching, yield and profitability of succeeding cotton in irrigated and dryland Vertosols were studied in nine on-station and on-farm experiments located in New South Wales and SE Queensland from 2002 to 2005. Key management issues considered were tillage systems, rotation crops and stubble management systems, and in particular, sowing cotton into standing wheat and vetch stubble. Soil physical and chemical properties were measured in all experiments. Soil water storage, crop growth, cotton lint yield and fibre quality were also measured. Economic returns in irrigated sites were evaluated by comparing seasonal and cumulative gross margins. Spatial and temporal deep drainage (with the chloride mass balance model) and nutrient leaching, and profile salinity change with an EM38 meter were measured in some NSW sites. Investigations were conducted into cotton crop management practices which could overcome problems associated with sowing cotton into standing (retained) rotation crop stubble. Residual effects of the rotation crops sown were present up to a period of five years with respect to soil structure, sodicity, exchangeable K, deep drainage and nutrient and salt leaching. Deep drainage, nutrient and salt leaching were generally in the order of ex-cotton-wheat > ex-continuous cotton > ex-cotton-dolichos. At the dryland site Qld, soil structural properties were affected primarily by tillage system (changing from conventional to zero tillage) with rotation crops affecting structure only during a period of relatively higher compaction. Least compaction occurred with double-cropped cotton-wheat. In most locations, sowing cotton into standing wheat stubble improved soil organic carbon, rainfall harvesting and gross margins (during the cotton phase of the rotation), decreased sediment concentration in runoff, soil sodicity and salinity; and improved cotton yields and root growth. When cotton prices were low cumulative gross margins with either conventionally-tilled continuous cotton or minimum-tilled cotton-wheat were similar. Irrespective of price, gross margins of minimum-tilled continuous cotton were highest. Sowing vetch as a rotation crop improved soil physical and chemical properties in good quality soil. In poor quality soil, vetch rotation crops reduced N fertiliser requirements and nitrate-N leaching, but no other soil improvement occurred. Cotton lint yield following vetch was similar to continuous cotton but less than after wheat or wheat followed by vetch. Gross margins of cotton-vetch were always lowest. At lint prices < $450/bale, gross margins of the cotton-wheat (standing stubble)-vetch rotation were highest. Retaining crop stubble in-situ can cause several problems such as blocking of "gas knives" during injection of anhydrous ammonia as fertiliser and waterlogging during irrigation. In addition vetch regrowth can suffocate emerging cotton seedlings. These problems were overcome by attaching coulter discs to the front bar of the gas rig to cut through crop stubble, removing stubble in furrows at the start of the irrigation season and controlling vetch regrowth through a combination of mechanical methods herbicides. Drainage was greater where cotton was sown into standing wheat stubble compared with stubble incorporation. Management practices which improved subsoil structure such as permanent beds or cereal rotation crops also resulted in more drainage. Stubble burning increased deep drainage. Yield losses of the order of 50% occurred when soil chloride levels in the 0-60 cm depth at sowing were of the order of 5.3 t/ha.
Appears in Collections:2005 Final Reports

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