| In order to explore the suitable nitrogen application rate and throwing density for ratoon rice production under the orderly machine-throwing mode,a field experiment was carried out in the scientific research base of Datonghu District,Yiyang City,Hunan Province from2020 to 2021.The ratoon rice variety Y Liangyou 911(YLY911)and Yongyou 4949(YY4949)was used as the test material.According to the split-plot test design,the main plot was the throwing density(D1:low density treatment,18.2×10~4holes/hm~2;D2:medium density treatment,25.0×10~4holes/hm~2;D3:high-density treatment,30.8×10~4holes/hm~2),and split plot was pure nitrogen application in the main season(N1:150 kg/hm~2,N2:195 kg/hm~2,N3:240 kg/hm~2,N4:285 kg/hm~2).The effects of throwing density and nitrogen application rate on yield and composition factors,population growth characteristics,and nitrogen absorption and utilization of ratoon rice were analyzed and compared.The main results were as follows:1.The density effect of yield in the main season and the ratoon season was consistent among varieties.The main season yield,ratoon season yield and annual yield of the medium and high density treatments were increased by 5.21%～5.70%,2.84%～4.46%,4.70%～4.95%respectively compared with those of the low-density treatments.The analysis of yield components showed that high effective panicles per unit area was obtained in the main season and ratoon season of medium and high density treatments.2.The effect of nitrogen application rate on main season yield was inconsistent among varieties.The main season yield of YLY911 increased first and then decreased with the increase of nitrogen application rate.The main season yield of N2 treatment was the highest at 9.65 t/hm~2,which was 5.12%higher than that of N1 treatment.The main season yield of YY4949 increased with the increase of nitrogen application rate.The main season yield of N3 and N4 treatments was the highest,which was 9.74 t/hm~2,which was 7.86%higher than that of N1 treatment.There was no significant difference in the yield of the ratoon season among the nitrogen application treatments.The analysis of yield components showed that the seed setting rate was higher under the premise that the YLY911 N2 treatment had higher effective panicles per unit area.YY4949 N3 and N4 treatments had higher effective panicles per unit area and grains per panicle.3.The effect of nitrogen application rate on annual yield was consistent among varieties.The annual yield of the two varieties increased first and then decreased with the increase of nitrogen application rate.The annual yield of YLY911 N2 and N3 treatments was higher,which was 2.21%-3.78%higher than that of N1 treatment.The annual yield of YY4949 N3 and N4 treatments was higher,which was 4.77%-6.04%higher than that of N1 treatment.4.The partial productivity of nitrogen fertilizer and the total nitrogen absorption in the main season,ratoon season and the whole year of the medium and high density treatments were higher than those of the low density treatment;With the increase of nitrogen application rate,the total amount of nitrogen uptake in the main season and the whole year gradually increased,while the nitrogen utilization rate decreased.The difference between nitrogen uptake and utilization in the ratoon season was not significant.To sum up,the suitable throwing density of orderly machine-thrown ratoon rice is 25.0×10~4～30.8×10~4holes/hm~2,the suitable main season nitrogen application rate of YLY911is 195～240 kg/hm~2,and the suitable nitrogen application rate of YY4949 is 240～285 kg/hm~2.Considering the principle of cost saving and increasing efficiency,the recommended seedling-broadcasting density is 25.0×10~4holes/hm~2,and the recommended nitrogen application rate in YLY911 is 195 kg/hm~2,and the recommended nitrogen application rate in YY4949 is 240 kg/hm~2. |
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