Optimum N applcation rate for high yield and nitrogen use efficiency of early maturing potato cultivar in red soil

Objects The response of yield and nitrogen use efficiency of potato, and the distribution of mineral nitrogen in soil were studied under different nitrogen application levels, aiming to propose a optimum nitrogen application rate in the potato production in red soil area of China.

Methods A field experiment was conducted in typical red soil area of south China in 2018 and 2019, and using a early maturing potato cultiva as test material. The treatments were seven N application levels (N 0, 60, 120, 150, 180, 210, 240 kg/hm²). At maturing stage, the yield and N contents of potato tuber and stalk, and the soil examples in 0–20, 20–40 and 40–60 cm deep were collected for determination of ammonia and nitrate nitrogen contents.

Results The potato yield, dry matter accumulation, N absorption and utilizationin varied greatly under different N application rates. Both the tuber yield and N accumulation were increased first and then decreased with rise in N rate, and the highest tuber yield (26250 kg/hm² in 2018 and 27915 kg/hm² in 2019) and the highest N accumulation (97.65 kg/hm² in 2018 and 101.09 kg/hm² in 2019) were achieved under N 180 kg/hm² treatment, while the stalk yield and N accumulation kept increased with the rise in N rate. The highest N harvest index was achieved at N150 kg/hm² treatment, and the highest agronomic efficiency and recovery rate of nitrogen were all under N 180 kg/hm² treatment, wherease the patial factor productivity of nitrogen kept decreased as the N rate increasing. The effect of N application rate on the content and distribution of mineral nitrogen in soil was different. The N 150 kg/hm² and N 180 kg/hm² treatment led significantly higher NH₄⁺-N contents than other treatments in 0–20 cm soil layer, but not in 20–60 cm layer; while the N 210 kg/hm² and N 240 kg/hm² treatment significantly increased the NH₄⁺-N contents in 20–60 cm layer. N rate of less than N 210 kg/hm² did not increase the NO₃^–-N contents in 0–60 cm soil layer, while the N 240 kg/hm² significantly increased that in 20–40 cm and 40–60 cm layers.

Conclusions The optimum range of N application rate is very narrow for early maturing potato cultivar. In red soil area, the highest buber yield, N use efficiency and relative high harvest index could only be achieved at N rate of 180 kg/hm², less or higher than the rate will decrease these indexes significantly. Also, the soil mineral N contents is high in 0–20 cm and not in deeper layer under N rate of 180 kg/hm², thus less possible of leaching into water.