Nutrient demand characteristics of early maturing rape cultivar in the area of triple-cropping system in south China

Objective The characteristics of dry matter (DM) accumulation and nutrient absorption of early maturing rape cultivar were compared with those of conventional one under the three-ripening system of rice-rice-rape rotation in southern China, so as to provide a reference for the nutrient managements of early maturing rape cultivars.

Methods Field experiments were conducted from 2017 to 2019 in Hengyang City, Hunan Province. The tested early maturing cultivar (EMC) was Xiangyou 420 and the conventional one (CMC) was Xiangyou 1035. Plant samples were taken every 15 days or so since 45‒50 days after sowing for the determination of the dry matter (DM) accumulation and the contents of N, P, K, B and Mg.

Results The accumulation of DM, K and Mg in EMC were lower than those in CMC, and averagely 11.2%, 6.3% and 11.0% lower, but the harvest index, seed yield and the accumulation of N, P and B were higher than those in CMC, and averagely 4.4%, 8.2%, 22.2%, 10.0% and 22.7% higher. The largest net increment of DM and P occurred in silique developing stage in EMC and in blooming stage in CMC. In 2017‒2018 and 2018‒2019, the net increment of DM were 6492 and 3559 kg/hm², accounting for 52.3% and 35.8% of the total accumulation in silique developing stage in EMC, and those of DM were 4975 and 4867 kg/hm², accounting for 37.1% and 41.8% of the total in blooming stage in CMC. The increment of P in the two years were 15.0 and 12.0 kg/hm², accounting for 47.5% and 31.7% of the total accumulation of P in silique developing stage in EMC, while the net P increment were 12.1和16.8 kg/hm², accounting for 44.1% and 46.1% in blooming stage for CMC in two years, respectively. The net increment of N were the largest in blooming stage for EMC and in seedling stage for CMC. During the stage in 2017‒2018 and 2018‒2019, the net increment of N were 62.8 and 46.2 kg/hm², accounted for 46.8% and 41.9% of the total in the blooming stage in EMC; while those were 53.0 and 51.5 kg/hm², accounted for 48.6% and 56.7% in seedling stage for CMC, respectively. Both EMC and CMC had the largest net K increment in flowering stage, but EMC also had the second highest net K increment in silique developing stage or in bolting stage, and CMC at the seedling stage. The maximum net K increment of EMC were 120.6 and 172.1 kg/hm², accounting for 39.9% and 66.8% of the total K accumulation, and the maximum net K increment of CMC were 105.8 and 145.0 kg/hm², accounting for 32.8% and 52.7% of the total K accumulation, the proportion of the highest net K increment in EMC were higher than those in CMC. In 2017‒2018, the highest net increment of B and Mg were in silique developing stage in EMC and in blooming stage in CMC. While in 2018‒2019, they were all in blooming stage, but the second highest net B increment in EMC (silique developing stage) was still lag behind CMC (bolting stage). The proportion of the highest net B increment was 47.5% and 58.4% for EMC, 64.3% and 54.9% for CMC, and the corresponding net increment was 237.9 and 249.7 g/hm² for EMC, 260.1 and 193.6 g/hm² for CMC. The percentage of net Mg increment in the highest period was 39.4% and 39.5% for EMC, 37.7% and 37.0% for CMC, and the corresponding net increment was 6.2 and 3.4 kg/hm² for EMC, 6.4 and 3.8 kg/hm² for CMC.

Conclusions The peak accumulation of dry matter and nutrients are mainly occurred from the seedling to the blooming stage in conventional maturity cultivar, and are from the flowering to the silique developing stage for early maturing cultivar. The nutrition demand in early maturing cultivar falls behind the conventional maturity cultivar, especially the peak requirement of nitrogen. Therefore, the supply of N, P, K, Mg and B fertilizers should be paid more attention from the flowering to the silique developing stage when early maturing cultivar of rape is used.