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

Abstract. Field trials were conducted at a gated pipe surface and overhead irrigation sites established to cotton to evaluate irrigation and fertigation management using a model-based control system. The control strategies determined the timing and volume of irrigation, and the rate of fertilizer-N to 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 soil N. Applying fertilizer 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 fertigation appears 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 that warrant 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.