Effects of smooth vetch (Vicia villosa Roth var. glabrescens) incorporation on nitrogen fertilizer replacement and soil fertility improvement in a maize-green manure rotation system

Objectives The study was conducted to evaluate the effects of smooth vetch (Vicia villosa Roth var. glabrescens) turnover amount on maize growth and soil properties in a maize-green manure rotation system. The aim was to provide theoretical support for the chemical fertilizer reduction potential of smooth vetch.

Methods The field trials were conducted in Songming County, Yunnan Province in 2018 and 2019, with the maize (Heinuo No.1) as test material. The experiment included five treatments: winter fallow (CK), incorporation of smooth vetch at 15000 kg/hm² (G1), 30000 kg/hm² (G2), 45000 kg/hm² (G3), and winter fallow with chemical fertilizer application N 270 kg/hm² (FN). The smooth vetch was planted during winter season and returned to field before maize cultivation. NPK content and accumulation in the aboveground part of maize, yield and yield components were examined at harvest, including soil total and available N, P, and K and organic matter content. The soil pH was measured as well.

Results The maize yields of treatments G1, G2, and G3 were equivalent to 78.14%, 88.88%, and 92.86% of treatment FN in 2018, and 98.92%, 104.22%, and 113.91% of treatment FN in 2019. However, the plant height, ear height, bald ear length, and single ear weight were not significantly different (P>0.05) among all the treatments. The grain N content of the FN treatment was (P<0.05) higher than other treatments, and the N content of its straw was significantly higher than that of CK and G1 treatments. In 2019, the N accumulation in the shoots of G3 treatment was (P<0.05) higher than those of FN and G1 treatments, which were 42.03% and 33.91%, respectively. In 2018, corn P accumulation in the FN treatment was significantly higher than those of CK and G1 treatments, with no difference in K accumulation among the treatments. Except for CK, there was no significant difference (P>0.05) in P accumulation among the four treatments in 2019. The three green manure treatments accumulated more K than the FN treatment. There was no difference in soil nutrients among the treatments in 2018. In 2019. soil available N, available K, total N, and organic matter content increased significantly, enhancing soil fertility as the green manure application increased. The aggregated boosted tree (ABT) analysis indicated that soil total N and single ear weight contributed the most to maize yield, both accounting for 20.89%.

Conclusions The incorporation of smooth vetch at a high rate in the first year (45000 kg/hm²) and moderate rate (30000 kg/hm²) in the second year relegates the need for N fertilizer in maize production. Smooth vetch incorporation at the above rates could provide similar or even higher N nutrition for maize to produce higher yields. After two years of incorporating smooth vetch, the soil total and available N and K and organic matter contents increased.