Soil constraints to productivity improvement
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Yields of most crops are known to decrease if that crop is grown continuously without fallowing or rotation with other crop species. Sugarcane has been grown continuously on many fields in Queensland for 50-100 years. As early as 1934 soil-borne factors which restricted root and shoot growth were identified in fields which had grown sugarcane for a number of years. During the 1970s nematodes were found to be causing serious losses in Bundaberg on certain soil types and a serious root disease complex known as poor root syndrome was identified in northern Queensland. During the 1980s intensive research into poor root syndrome identified the important new disease Pachymetra root rot and a number of minor fungal pathogens. Poor root syndrome has been identified in all regions of Queensland and general poor root health has been noted in all soils which have grown sugarcane for a number of years. Yield increases of 50-100% were obtained in areas severely affected by poor root syndrome in northern Queensland by soil fumigation with methyl bromide and metham sodium, and by soil solarisation. Recent experiments have recorded yield responses of 20-40% to methyl bromide fumigation in all major sugarcane regions. These experiments suggested that yield losses due to soil-borne factors may be greatly restricting yields throughout the sugar industry. Research to identify the causes of the yield losses has commenced and progress to date is summarised in this paper.