Effect of fertigation on crop and soil established to cotton (Gossypium hirsutum L.) under furrow and overhead irrigation

摘要

Field trials were conducted at a gated pipe surface and overhead irrigation sites established to cotton to evaluate irrigation andfertigation management using a model-based control system. The control strategies determined the timing and volume of irrigation, and the rate offertilizer-Nto apply via fertigation. Nitrogen was applied as urea ammonium nitrate (UAN, 30% N, solution) at an average rate of 40 kg ha~(-1) N. For the furrow irrigated system, this study showed satisfactory uniformity of distribution of fertilizer-N applied during the irrigation events, which was achieved both at distance (furrow length: 600-m) and depth (0-600 mm). Greater control over the water applied to furrows will likely reduce deep percolation of native soilN. Applyingfertilizer using fertigation showed relatively small (<8%) improvements in cotton yield, which was explained by high N rates (-180 kg ha~(-1) N) applied prior to planting. Given current price ratios (nitrogen-to-cotton), application of N via fertigationappears to be economical in both systems, but relative agronomic efficiencies and economic return from fertilizer applied were lower in the furrow compared with the overhead system (P<0.05). Despite this, fertigation appears to be a cost-effective technique for application of N fertilizer in-crop season, particularly, when pre-plant N application rates are lower than those used in this study. For the overhead system; this study also showed advantages compared with the furrow system in terms of reduced potential for N2O emissions after fertigation. Short-term N2O emissions were approximately seven times higher in the furrow compared with the overhead system (P<0.05); and emissions were highest within three days of fertigation in both systems. Areas thatwarrant further investigation are presented and discussed; including the need for improved timing of fertilizer delivery during the irrigation event to ensure that N losses by leaching and gaseous evolution are not economically or environmentally significant.