Water-phosphorus coupling enhances fine root turnover and dry matter yield of alfalfa under drip irrigation

Alfalfa (Medicago sativa L.)is an important forage with high quality and fine root turnover rate (FRTR). Soil phosphorus (P) availability greatly influences dry matter yield (DMY) and persistence of alfalfa. However, the effects of water (Wa)-P coupling under drip irrigation conditions on alfalfa FRTR and DMY have been rarely studied. Therefore, a 2-yr field experiment was established with three randomized complete blocks in Xinjiang, China, evaluating three irrigation amounts (5,250, 6,000, and 6,750 m(3) ha(-1), referred to as W-1, W-2, and W-3, respectively) and four P application rates (0, 50, 100, and 150 kg ha(-1), referred to as P-0, P-1, P-2, and P-3, respectively) in 2017 and 2018. The Wa-P interaction had a significant effect on alfalfa DMY (P < .05), and DMY reached the maximum at W2P2 treatment. Fine root biomass (FRB) presented a bimodal pattern over time (on 21 June and 20 August) and mainly existed in the soil layers 20-40 cm underground. All root variables including FRB were positively correlated with alfalfa DMY. Comprehensive analysis showed that W2P2 was the optimal treatment of the 12 treatments. Therefore, the irrigation amount of 6,000 m(3) ha(-1) and P application rate of 100 kg ha(-1) seems beneficial to achieve the relatively rational FRTR and the greater DMY of alfalfa.

Automated summary

The study showed that the coupling of water and phosphorus under drip irrigation conditions significantly affected the dry matter yield of alfalfa, with the highest yield observed in the W2P2 treatment, indicating that an irrigation amount of 6,000 m(3) ha(-1) and P application rate of 100 kg ha(-1) were beneficial for alfalfa root turnover rate and dry matter yield.