Water productivity and production function in irrigated millet crop

Determining the function that correlates water productivity with crop yield is essential for the correct sizing and management of irrigated agricultural systems. The objectives of this study are to determine forage production (FP) of millet at different irrigation levels and water productivity. Two experiments were conducted using millet crop sown in the 2014/2015 growing season in Santiago, Rio Grande do Sul, Brazil, and in the 2015/2016 growing season in Santa Maria, Rio Grande do Sul. The experiments were carried out using a completely randomized block design with four repetitions and six irrigation regimes (0, 25, 50, 75, 100, and 125% of reference evapotranspiration-ETo). Dry matter (DM) production of plants collected at 50, 80, 110, and 140 days after sowing and water productivity were determined. Irrigation had a significant effect on millet FP (kg DM ha-1) during the 2014/2015 and 2015/2016 growing seasons after adjusting the quadratic equation. The maximum technical efficiency in the two growing seasons was reached at 125% of ETo, with FP of 15,494.47 kg ha-1 and 14,779.50 kg ha-1, respectively. Water productivity was not significantly different between treatments, yieldingan average of 1.86 kg DM m-3 and 1.69 kg DM m-3 in the two seasons, respectively. The curve of average FP estimated with the logistic equation accurately represents the total FP in the two seasons. Millet crop is susceptible to water deficits, and the irrigation regime of 125% ETo achieved the highest FP in both growing seasons. However, the adopted irrigation regimes did not significantly affect water productivity.