氮肥用量对旱地冬小麦产量及夏闲期土壤硝态氮变化的影响

EFFECTS OF NITROGEN APPLICATION RATE ON WINTER WHEAT YIELD AND SOIL NITRATE NITROGEN DURING SUMMER FALLOW SEASON ON DRYLAND

在陕西渭北旱塬，利用长期定位试验研究了长期不同氮肥用量（0、80、160、240、320 kg hm-2）对旱地冬小麦产量形成，氮素利用，土壤硝态氮残留、夏闲期淋溶和矿化的影响。结果表明：随用量增加，施氮提高旱地小麦产量的效应下降，而土壤硝态氮残留迅速增加。作物生长当季的硝态氮残留主要分布在0～60 cm土层，施氮超过160 kg hm-2时，达56.8～211.7 kg hm-2，来源于当季施用氮肥的残留占64%～90%。夏闲期土壤硝态氮发生淋失的土层深度和硝态氮淋失量均与施氮量呈显著的抛物线关系（r = 0.988 9和0.994 0），施氮量超过160 kg hm-2时，每增加100 kg hm-2的氮肥投入，硝态氮淋失深度和淋失量增加量分别高于27 cm和80.4 kg hm-2。平均每10 mm的夏闲期降水可使离开原土层发生淋溶的硝态氮向下移动2～4 mm。施氮量对硝态氮淋失的深度没有显著影响。夏闲期土壤氮素矿化量、来源于当季施入土壤肥料氮被生物固定后的再矿化量分别为51.8～160.9 kg hm-2和31.6～109.2 kg hm-2。基于本研究，建议渭北旱塬冬小麦施氮量控制在146～163 kg hm-2，以保证旱地小麦高产，防止过量肥料氮残留，减少淋溶风险。

Based on an eight-year long stationary field experiment on Weibei Arid Tableland in Shaanxi Province, China, effects of Nitrogen （N） application rate on grain yield and nitrogen utilization, N residual, nitrate leaching and organic N mineralization in dryland soil were investigated with winter wheat as test crop. The experiment was designed to have 5 N application rates, i.e. 0, 80, 160, 240 and 320 kg hm-2. Results show that with increasing N application rate, the response of wheat in yield to N application weakened, whereas nitrate N residue in the soil rapidly increased. The nitrate N residue from the current wheat growing season was mainly distributed in the 0 - 60 cm soil layers, and when N application rate was raised beyond 160 kg hm-2, it reached up to 56.8 - 211.7 kg hm-2 in content of which 64% - 90% was found derived from the N fertilizer applied before seeding. Depth of the soil layer where leaching of nitrate occurred and amount of the nitrate N leached from the corresponding layer during the summer fallow season were all positively and parabolically related to N fertilizer rate, （r = 0.988 9 and 0.994 0）. When N application rate went beyond 160 kg hm-2, every increment of 100 kg hm-2 of N would increase the depth of nitrate leaching by 27 cm and the amount of nitrate N leached off by 80.4 kg hm-2. On average, every 10 mm of rainfall during the summer fallow season would have nitrate N leached 2 - 4 mm deeper. However, N application rate did not have much effect on depth of nitrate leaching. During the summer fallow season, soil N mineralization reached 51.8 - 160.9 kg hm-2 of which 31.6 - 109.2 kg hm-2 was found to be N from the fertilizer applied for the current crop, fixed by soil microbes and then remineralized. Based on such findings, it is advisable to suggest that the N application rate for winter wheat in the region should be controlled within the range of 146～163kg hm-2, so as to guarantee high winter wheat yields, and prevent excessive residue of fertilizer N in the soil and reduce the risk of nitrate N leaching.