Nutrient uptake and export from an Australian cotton field

Soil fertility may decline as a result of nutrient export from high-yielding cotton crops and this may limit the productivity of future crops unless these nutrients are replaced. Uptake of nutrients by cotton (Gossypium hirsutum L.) and nutrient export from the field in seed were measured within two cropping systems experiments from 1999 to 2005 in a flood-irrigated cotton field. Lint yields of the seven crops assessed ranged from 975 to 2725 kg lint/ha. Nutrient uptake was measured at mid to late boll-fill and nutrient removal determined from analysis of delinted seed. Cotton crops accumulated an average of 180 kg N/ha (range 67–403), 27 kg P/ha (range 18–43), 167 kg K/ha (range 88–264), 41 kg S/ha, 160 kg Ca/ha, 36 kg Mg/ha, 7 kg Na/ha, 890 gm Fe/ha, 370 gm Mn/ha, 340 gm B/ha, 130 gm Zn/ha and 51 gm Cu/ha. On average, the seed within harvested seed cotton removed 93 kg N/ha (range 38–189), 18 kg P/ha (range 8–34), 29 kg K/ha (range 13–51), 8 kg S/ha, 4 kg Ca/ha, 12 kg Mg/ha, 0.2 kg Na/ha, 136 g Fe/ha, 12 g Mn/ha, 41 g B/ha, 96 g Zn/ha and 20 g Cu/ha. Nutrients contained in the lint and trash were not included. For crops yielding about 1800 kg/ha, 70% of the Zn and P taken up was removed in the seed, also 52% of N, 38% of Cu, 34% of Mg, 21% of S, 17% of K and Fe, 12% of B and only 3% of Ca, Mn and Na. Predictive equations were developed to allow growers to estimate the removal of nutrients given the lint yield measured from their cotton crops.