豆类作物施用氮肥在生物学与经济学上的意义Paul W. Singleton* Nantakorn Boonkerd* James R. Hollyer*夏威夷大学热带农业和人类资源学院 Nif TAL 项目* Suranaree 技术大学 农业生物技术系* 夏威夷大学热带农业和人类资源学院农业和资源经济系*1. 引言?Introduction豆类作物同化氮素有两种形式，它不仅可以同化来自土壤及肥料的无机氮，也可以通过生物固氮从大气中捕获氮气。生物固氮过程是利用植物根瘤中产生的细菌酶把N2还原成有效形态。根瘤是共生细菌（根瘤菌属）侵入根毛后形成的，豆类作物光合作用为共生固氮共生体提供能量。Legumes have two modes of nitrogen assimilation. Although legumes assimilate mineral N from soil and fertilizer sources, they also capture N from the atmosphere through biological dinitrogen fixation (BNF). The BNF process reduces N2 to plant available forms using bacterial enzymes produced within root nodules. The root nodules are formed after the symbiotic bacteria Rhizobium invades root hairs. Legume photosynthesis provides the energy that drives the BNF symbiosis.豆类作物依靠生物固氮作为氮源的程度取决于以下因素的相互作用：The extent to which legumes rely on BNF as an N source is determined by an interaction between:1) 达到作物产量潜力所需的氮素总量；1) total amount of N required to meet crop yield potential;2) 土壤中有效态无机氮的数量；2) amount of mineral N available in the soil, and;3) 形成豆类作物根系根瘤的根瘤菌的效果。 3) effectiveness of rhizobia forming nodules on legume roots大多数豆类作物管理策略目的是最大限度地促进生物固氮。在作物生长期间，生物固氮过程直接受土壤矿质氮供应比例的抑制，要加大生物固氮量，豆类作物必须利用少量矿质氮以在生物固氮全面发挥前维持幼苗生长。Most legume management strategies aim to maximize BNF. During most of crop duration, the legume BNF process is inhibited in direct proportion to soil supply of mineral N. To maximize BNF, however, legumes must assimilate a small amount of mineral N to sustain early crop growth prior to full expression of BNF.豆类作物的氮素管理有两种常用方法。一种是接种优良的根瘤菌使其生物固氮量足以满足作物的大部分需要。接种技术和接种剂产品很多，为农民提供了最大限度促进作物生物固氮的廉价选择。另一种选择是施氮肥。许多农民在种植豆类作物时施用少量氮肥（1050公斤N /公顷），而另一些农民并不依靠生物固氮，仍然施用大量氮肥。There are two common practices for managing legume N nutrition. Inoculating legumes with superior rhizobia ensures that BNF can meet most of the crops N requirement. Inoculation techniques and inoculant products are well developed and provide farmers an inexpensive option to attain maximum BNF by their crops. Another option is t apply fertilizer N. Small amounts of N (10-50 kg N ha-1)are applied by many farmers when planting legumes (starter N). Others apply larger quantities of N fertilizer and do not rely on BNF to any significant extent. 对豆类作物推荐施种肥是因为我们知道在出现生物固氮之前豆科植株对矿质氮有生理依赖。然而，在对农民进行施氮肥推荐时，通常不能考虑土壤有效氮对作物早期生长对矿质氮的实际需要。在大多数情况下，上季作物残留的氮加上由有机物分解的矿质氮就足够豆类作物早期生长的需要。Recommendations for starter N originate from our knowledge of the legumes physiological dependence on mineral N prior to onset of BNF. Starter N recommendations to farmers, however, usually fail to account for soil available N relative to the crops actual requirement for mineral N during early growth. Most often, residual N from previous crops plus mineralized N from organic matter are sufficient to meet the early N requirements of legumes.在各种土壤类型和气候条件的大面积上遵循施氮推荐在生物学和经济学上的潜在费用是巨大的。例如，1994年估计有538,165吨氮肥施在了中国17个省的1050万公顷的大豆及花生上（钾磷研究所，Sam Portch私人通信），仅这一氮管理措施的直接投入费用就高达26.32亿元人民币。生物固氮潜力捕获的氮减少了215000吨以上?-假设氮肥利用率为40%，如果对豆类作物生物固氮管理得当的话，只以小部分氮肥成本就可获得这些氮。The potential biological and economic costs of following recommendations for starter N across large areas with variable soil types and climates are enormous. For example, in 1994 it was estimated 538,165 metric tonnes (mt) of N were applied to 10.5 million ha of soybean and groundnut crops across 17 provinces of China (Potash & amp; amp; Phosphate Institute, Sam Portch personal communication). Direct input cost alone of this N-management option could be as high as 2,632 million RMB ($317 million U.S.). Reduction in potential capture of N from the BNF process could exceed 215,000 mt - assuming an FUE for N of 40%. This N could be obtained at a small fraction of the cost of N fertilizer by properly managing legume BNF.氮的生物学反应与其成本之比和将这些财力资源用于其他管理选择的预期经济收益决定着施氮肥是否作为一种推荐管理措施。本文在生物学及生态学方面评述豆类作物的氮肥管理，并进一步评估了在中国对豆类作物的氮肥管理选择的经济费用和收益，包括施用氮肥和非氮肥投入的机会成本。Whether N fertilizer should be a recommended management practice is determined by biological response to N relative to its costs and the foregone economic benefit from using these financial resources for other management options. This paper reviews the biological and ecological aspects of N-management of legumes. Further, it evaluates the economic costs and benefits of N-management options for legumes in China including opportunity costs of N fertilizer use in relation to non-N fertilizer inputs.2. 豆类作物对氮的需要和吸收?Nitrogen Requirements and Uptake by Legumes2.1 豆类作物在农业上的重要性 Importance of legumes in agriculture籽用豆类是世界农业中第二重要的作物。通过直接食用和转化为动物产品，它们是重要的食物蛋白的来源。在许多发展中国家豆类蛋白占蛋白质消耗的大部分；在一些发达国家及那些经济快速增长较不发达国家，对豆类蛋白需求的增长速度超过了对谷物需要的增长。收入的增加加速对动物蛋白与豆类作物这种动物原料的需求。在很多情况下，豆类作物生产的增加反映了畜牧生产的变化。例如，在19801992年间，中国畜牧业迅速增长，在同一时期，大豆及花生生产也提高了，豆类作物生产的增加几乎完全是来自管理措施的改进。改进作物管理与产量潜力的一个标志是磷肥与钾肥的施用量的急剧增加。本文将说明管理的改进与豆类作物高产是农民从生物固氮中获得最大利益的条件。Grain legumes are the second most important crop in w