Absorption and distribution of nitrogen, phosphorus and potassium in onion

The growing characteristics of onion planted in autumn and its absorption and distribution rule on nitrogen, phosphorus and potassium were studied. The results showed that dry matter accumulation in onion at the seedling stage was very slow and absorption speed of the nitrogen, phosphorus and potassium was very low, which only accounted for about 4% of the whole nutrient. At plant vigorous growth stage, the uptake rates of N, P2O5, K2O were 22.03, 8.60 and 15.65 mg/(plant·d), accounted for 92.74%, 91.01%, 71.79% of nutrient uptake during the whole growing stages. At the bulb expanding stage, the uptake rate of N and P2O5 decreased rapidly, but the rate of K2O was still kept at 7.23 mg/(plant·d). The proportion of onion absorption to N, P2O5 and K2O was 1:0.40:0.92 taking the whole growing stages into consideration. The absorption rate of phosphorus and potassium increased with onion growing, and reached 1:0.92:9.04 at the bulb expanding stage. Nitrogen, phosphorus and potassium were mainly distributed in leaf at the seedling stage, in bulb and leaf at the plant vigorous growth stage and in bulb at the bulb expanding stage, with distribution rate being 75.88%, 87.7% and 71.81%, respectively. The demands for N, P2O5 and K2O were about 2.93, 1.16 and 2.69 kg for every 1000 kg bulb product, respectively.