Trade‐offs between forage crop productivity and soil nutrients for different ages of alfalfa grassland

Abstract

AbstractObtaining sustainable high yield and suitable soil nutrient management is crucial for cultivate alfalfa grassland. However, the information on the trade‐offs between soil nutrient and productivity of alfalfa grassland following long‐term cultivation under intensive agricultural management is scare. Six alfalfa grasslands of different ages under a highly intensive agricultural management system were chosen for this study. It was shown that long‐term planting of alfalfa reduced soil nutrients overall. In the 0–100, 100–200, and 200–300 cm layers, the highest values of soil organic carbon (SOC), soil total nitrogen (TN), and soil total phosphorus (TP) content were observed in one‐year‐old alfalfa grassland. SOC, TN, and TP contents in each 100 cm soil layers linearly declined with increasing stand age, and decreasing rates of SOC and TN (4.31 and 0.03 g kg−1 yr−1) in the 0–100 cm layer were higher than other two soil layers. The SOC storage (SOCS) and TN storage (TNS) in 0–20 cm soil were significantly higher than other soil profiles in six alfalfa grasslands of different ages. SOCS and TNS in 0–100 cm, especially in upper 40 cm soil, decreased over time until the fourth year, and gradually increased in the fifth and sixth years. While in the third and fourth years, productivity reached peak value (3.13 and 3.12 t ha−1), and then reduced. Correlation analysis showed productivity was significantly negatively correlated with SOCS and TNS in 0–100 cm soil depth. The decline in soil nutrients affected alfalfa growth and then feedback its productivity, and the optimal stand age of alfalfa grasslands should not be longer than 6 years for the limitation of soil nutrient, especially SOC storage. To acquire sustainable high productivity of artificial alfalfa grassland, our study suggested that more organic and nitrogen/phosphorus fertilizers should be applied to the upper soil layer beginning in the third year after planting.