Effects of irrigation and phosphorus fertilization on alfalfa yield and water and fertilizer use efficiency

【Objectives】Alfalfa (Medicago satiua L.),a very important forage crop in animal husbandry, consumes large quantity of water for growth. One of the important limit factors for alfalfa production is water deficit in the region of south Beijing including Jixian County and Baodi District, Langfang City and Wuqing District. The alfalfa yield in this region is only 7500-10000 kg/ha, and even as low as 4500-6000 kg/ha in saline soils. Therefore, suitable drip irrigation technology and phosphorous fertilization in alfalfa production was studied.【Methods】A field experiment was conducted in a loamy sand soil. The alfalfa yield and water and fertilizer use efficiencies were investigated. Four irrigation treatments include: no irrigation (W0),watering 25 mm (W1), 50 mm (W2) and 75 mm (W3) each time, and three irrigations totally in a year period. P fertilizer were applied twice after alfalfa turning green and second cut, respectively. The application rate treatments include: 0 (F0), 105 (F1) and 210 (F2) kg/ha P2O5. 【Results】Irrigation significantly impacts the dry matter yield of first and second cuts of alfalfa, not increase those of 3rd and the fourth cuts and the total annual yield of alfalfa. P application significantly affects the dry matter yield of the first, second and fourth cuts of alfalfa, as a result, significantly increase the annual yield. The highest yield (16589.4 kg/ha) is obtained with the treatment of 50 mm each irrigation plus 210 kg/ha of P fertilizer. Both water and P fertilizer use efficiency depend significantly on the watering amounts and P fertilizer levels. Alfalfa has high water use efficiency under the high amount of P fertilizer, indicating the positive effect of P fertilizer on alfalfas water use efficiency. Meanwhile, appropriate watering amount can improve P fertilizer use efficiency. The alfalfa yield, water and fertilizer use efficiency with treatment of W2F2 are higher than all the other treatments. 【Conclusions】The optimal watering amount is 50 mm each time and three irrigations in total, the suitable P fertilizer rate is 210 kg/ha for alfalfa in the south region of Beijing.