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。
Plant growth and crop production depend to a large extent on soil N supplying capacity （SNSC）： The higher the SNSC, the higher the dependence of crops on soil and the lower the N fertilizer recovery. Of the SNSC, soil organic N （ON） played a key role in supplying N nutrient to crop production and still does in many subsistence and low-input farming systems. In this paper, soil ON contents, types, chemical components and its contribution to plant production are reviewed up to date in details, the characteristics of ON in dryland soils discussed together with its chemical components, and the mineralization and availability to plants of some important chemical components are emphasized at the last part for practical considerations.
