Improvements in nutrient uptake and nutrient use-efficiency in cotton cultivars released between 1973 and 2006

We examined twelve cotton (Gossypium hirsutum L.) cultivars that were released in Australia between 1973 and 2006, in three field experiments, harvested in 2009, 2010 and 2012. Crop biomass and nutrient uptake were measured at 160 days after sowing and lint yield at crop maturity. Crop nutrient use-efficiency was determined by dividing lint yield by nutrient uptake. Lint yield increased by 40% (P < 0.001) for cultivars released between 1973 and 2006; crop biomass increased by 25%; N, S uptake increased by 20%, and 26% respectively; 33% for Ca, Mg and Na; and 22% for trace elements Fe, Mn, B, Zn and Cu (all P < 0.001). With the release of improved cultivars, the use-efficiency increased for N (20%, P < 0.001), P (23%, P < 0.001) and K (24%, P < 0.01). Similar increases were found for trace elements Fe, Cu and Zn (P < 0.05–0.001). Newer cultivars also had substantial improvements in lint fraction, fibre strength and fibre length. We conclude that crop nutrient use-efficiency has increased relatively slowly, crop nutrient uptake has increased faster but neither has increased as quickly as lint yield. Improved use-efficiencies of N, P, K, Fe, Zn and Cu have occurred through selective breeding for lint yield over the past three decades. Based on nutrient demand, it is calculated that further increases in yield will require improved nutrient use-efficiency, and probably with better internal redistribution of nutrients. Such research should be done using a soil type and growing system capable of producing high-yielding cotton.