Nutrient characteristics of soil sowed with different combinations of alfalfa and three perennial grasses

We evaluated the nutrient characteristics of soil sowed with different combinations of alfalfa and three grasses, namely, Bromus inermis, bluegrass, and tall fescues at ratios of 1∶1, 1∶2, and 2∶1. The effects of different combinations and ratios on soil nutrients in the 0 – 20 cm and 20 – 40 cm soil layers were evaluated. The results revealed the following. 1) The combination of alfalfa and three perennial grasses can significantly promote the accumulation of soil organic matter, available potassium, soil hydrolysis nitrogen, soil available phosphorus, and total phosphorus (P < 0.05). 2) Alfalfa + B. inermis was better than the other two combinations in improving soil fertility. The combination of alfalfa + B. inermis was more conducive to the accumulation of soil organic matter, nitrogen, and phosphorus nutrients in the 0 – 40 cm soil layer, whereas the effect of alfalfa + bluegrass in improving potassium accumulation was more obvious. 3) The ratio of alfalfa and the grasses had a significant effect on available phosphorus, total phosphorus, deep soil organic matter, and hydrolysis nitrogen in the shallow soil layer (P < 0.05). The soil nutrient content increased with an increase in alfalfa proportion. Among the three ratios, the 1∶1 ratio of alfalfa + B. inermis in the 0 – 20 cm soil layer and the 2∶1 ratio of alfalfa + B. inermis in the 20 – 40 cm soil layer were more conducive to the accumulation of available nutrients. In the 0 – 20 and 20 – 40 cm soil layers sowed with alfalfa + bluegrass at a ratio of 1∶2, soil available potassium and total potassium content was the highest, and at the ratio of 2∶1, the content of soil available nitrogen, total nitrogen, and total phosphorus was the highest. The content of organic matter, total nitrogen, total phosphorus, total potassium, and available nutrients in the 0 – 20 and 20 – 40 cm layers of soil sowed with alfalfa and reed fescue at 2∶1 ratio was higher than that at the other two ratios. 4) In terms of spatial distribution, except for single sowing of bluegrass and combination alfalfa + tall fescue, under all other combinations, the shallow soil nutrient content was higher than that in deep soil, showing a phenomenon of nutrient surface cohesion.