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Plastic film mulch promotes high alfalfa production with phosphorus-saving and low risk of soil nitrogen loss

Gu, Yan-Jie, Han, Cheng-Long, Kong, Meng, Shi, Xiao-Yan, Zdruli, Pandi, Li, Feng-Min
Field crops research 2018 v.229 pp. 44-54
Medicago sativa, alfalfa, carbon nitrogen ratio, experimental design, fertilizer application, forage yield, microbial biomass, microbial carbon, mineralization, mulching, nitrogen, phosphorus, phosphorus fertilizers, planting, plastic film mulches, risk, semiarid zones, soil microorganisms, soil organic carbon, soil water, total nitrogen, China
Plastic film mulch and phosphorus (P) fertilization usually increase alfalfa (Medicago sativa L.) forage yield in semi-arid regions by improving soil moisture and P availability. However, this does not always occur. The present study explored the P level for highest forage yield under film mulch and the mechanism underlying yield decrease at high P levels. A six-year study was conducted with randomized blocks of split-plot design with and without plastic film mulch as main plots: M0, no film mulch with flat planting; and M1, film mulching with ridge-furrow field regimes. Four P rates were applied in sub-plots: P0, P1, P2 and P3 with 0, 9.73, 19.3 and 28.9 kg P ha–1, respectively. Film mulch greatly increased forage yield, resulting in 14% higher yield in M1P0 than in M0P3. Forage yield under mulching decreased for 19.3 and 28.9 kg P ha−1. The P rate for maximum yield was 16.1 kg P ha−1. Soil total nitrogen (N) and inorganic-N decreased at 19.3 and 28.9 kg P ha−1 with mulching compared with 9.73 kg P ha−1, and the latter was about 90% lower than that of alfalfa lands in semi-humid region. Soil microbial biomass carbon (C) and C/N ratio in microbial biomass in mulched P2 and P3 subplots were significantly lower than for P1. With mulching, soil organic C mineralization was significantly less for P3 than for P1 and P2. Shoot N/P ratio decreased with increasing P with mulching. Thus shoot N uptake for P2 and P3 mulched plots was associated with low soil N availability. It is concluded that the highest forage yield was obtained with mulching, P-saving and low risk of N loss on the semiarid Loess Plateau.