Effect of fertilizer amount on yield and nutrient accumulation of green manures

The abundant winter fallow fields in southern China can be used to cultivate green manure crops. It has been demonstrated that returning green manure to farmlands supports sustainable agricultural development. Green manure yield has, however, decreased sharply in recent years, seriously limiting large-scale applications of green manure in agricultural production. A field experiment was conducted to study the effect of nitrogen (N), phosphorus (P) and potassium (K) fertilizers on yield and nutrient accumulation of green manure. The crops considered for use as green manure in this study included Astragalus sinicus L. and Alopecurus aequalis Sobol., which were studied in 11 treatments. A. aequalis was a natural reseeding gramineae grass grown in A. sinicus field. For more accurate analysis, 2 types of green manure were separately harvested and weighted. Results showed that fertilizer application significantly increased fresh yield of two plants. Compared with non-fertilizer treatments, yield under fertilizer treatments increased by 42.8%~311.1%. Compared with nutrient deficiency treatment, N, P and K treatments increased yield by 57.1%~177.5%, 27.8%~178.7% and 14.2%~32.4%, respectively. Fresh yields of the 2 green manures increased with increasing application rates of N, P, K. Fresh yield of A. aequalis was higher than that of A. sinicus under the medium and high application amounts of N and P fertilizers. For all K fertilizer treatments,A. aequalis produced higher fresh yield than A. sinicus. Green manure nutrient accumulation increased with increasing N, P, K application rate. Under medium and high N and P treatments, N and P accumulations in A. aequalis were higher than those in A. sinicus. However, K accumulation in A. aequalis was higher than that in A. sinicus for all K treatments. With 112.5 kg·hm^-2, 19.7 kg·hm^-2 and 37.5 kg·hm^-2 of N, P and K fertilizer application rates, total yield and C, N, P and K accumulations of two plants were maximum, reaching 49 424 kg·hm^-2, 3 212 kg·hm^-2, 151 kg·hm^-2, 19.8 kg·hm^-2 and 156 kg·hm^-2, respectively. Meanwhile, yield and C, N, P and K accumulations in A. aequalis accounted for 59.0%, 65.7%, 66.3% and 64.4% of the above total amounts. Those indicated that A. aequalis was a high quality green manure with a little input.