氮肥减施对稻-麦轮作体系作物氮素吸收、利用和土壤氮素平衡的影响

田间试验研究了稻-麦轮作体系中减施氮肥对作物氮素吸收、利用和土壤氮素平衡的影响。结果表明,与当地习惯施肥(小麦:N 225 kg/hm2,基肥与分蘖肥各半;水稻:N 210 kg/hm2,基肥和分蘖肥为3∶2)相比,减氮20%～30%处理产量并没有降低,而氮肥当季利用率、氮素农学利用率以及氮素偏因子生产力则有所增加;而且,氮肥分次追施,能增加子粒产量,并减少氮肥成本。虽然减氮20%～30%处理0—40 cm土层无机氮含量较习惯施肥处理降低,但是并没有降低植株地上部对氮素的吸收。在小麦和水稻收获期,减施氮肥处理0—100 cm土壤无机氮残留量低于习惯施肥处理;且稻-麦轮作系统中氮的表观损失主要发生在水稻季。初步认为,在长江中下游平原稻-麦轮作体系氮素过量施用地区,第一个轮作周期减施氮肥20%～30%不仅不影响产量,而且可提高氮素利用率,有利于保护环境。

Effects of reducing N application on crop N uptake, utilization, and soil N balance in rice-wheat rotation system

The effects of reducing N application on plant N uptake, utilization, and soil N balance in rice wheat rotation system were studied using field experiments. The results show that compared with farmers practice for N fertilization, N 225 kg/ha for wheat with 1/2 basal and 1/2 topdressing at the tillering stage and N 210 kg/ha for rice with the ratio of 3∶2 for the basal and tillering applications, the grain yields are not decreased under the N application amounts with a reduction by 20%-30%, while the N recovery efficiency, N agronomic efficiency, and N partial factor productivity are increased. Moreover, topdressing N fertilization can increase the grain yields and reduce the cost of the fertilization. Although both soil mineral N content and accumulation are reduced, the N absorptions by crops are not reduced accordingly. There is less residual soil mineral N in 0-100 cm layer at the harvest stages of wheat and rice compared to that of the farmers practice. In addition, the loss of apparent N in the rice wheat system is mainly occurred in the rice season. Therefore, it is preliminarily concluded that the reducing N application by 20%-30% is a feasible N management practice under the first rice wheat rotation system in the middle lower Yangtze plain with over N fertilization.