Dynamics of Roots and Nitrogen in Cropping Systems of the Semi-Arid Tropics-猫眼课题宝

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1996-03

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O. Ito;R. Matsunaga;K. Katayama;S. Tobita;J. Adu-Gyamfi;J. Kashiwagi;T. P. Rao;G. Devi

1984年，日本政府（GOJ）与国际半干旱热带作物研究所（ICRISAT）达成协议，建立一个题为“33 34 JJRCAS中高地作物种植的发展”的合作研究项目。1996年第3期《半干旱热带》。在这个框架内，科学家们在该项目的第一阶段（1984-1989年）集中研究了半干旱热带（SAT）的豆类作物的磷（P）营养。在该项目的第二阶段（1989 - 1994年），科学家们重点研究了种植系统中，特别是以木豆为基础的间作系统中的根系和氮的动态。以木豆为基础的间作被沙特资源贫乏的农民广泛采用。五年期活动的重点概述如下。采用指数拟合法对木豆根长的剖面分布进行拟合，发现木豆的根向水平方向的伸展量小于高粱、珍珠粟、花生和豇豆，而向垂直方向的伸展量大于高粱。一个基于天气和土壤数据的模型预测，木豆的生根锋的进展更快，相同的生理年龄。氮素吸收动力学研究表明，木豆对土壤和肥料氮的利用效率与其他缺乏生物固氮能力的作物相当，表明木豆与间作的其他伴生作物如谷类作物对氮素存在相当大的竞争。为了减少对外部氮的竞争，重要的是增加木豆对生物固氮的依赖。根呼吸的测定表明，木豆将投入相当高的呼吸能量吸收氮。用陶瓷多孔杯提取的土壤溶液中的硝酸盐（NO_3-N）浓度在种植季节开始时最高，此后迅速下降。土壤溶液中的NO3-N浓度降低，并且在播种后两个月记录为零值。据估计，100-150公斤公顷· 1之间的矿化N的量在土壤溶液中检测到50厘米土壤深度内，播种前。这表明，相当数量的N可用于作物吸收养分有限的淋溶土在生长初期。15 N标记和15 N天然丰度研究表明，作物不同氮源之间的氮平衡表，即，间作会改变土壤氮、肥料氮和大气氮，使生物固氮氮的比例增加。尿素的应用高粱行上级广播和分割应用，播种后一个月延迟应用上级基础应用（播种前）的一个组件高粱作物的氮利用效率（NUE），虽然生物量产量不受影响。延迟施用是有利的，因为如果由于降雨量不足而导致作物生长失败，则不会产生肥料成本。为提高间作资源利用率，建议木豆与高粱等根系较浅、氮素吸收效率较高的作物间作。此外，建议在氮从土壤溶液中消失之前延迟施氮，这通常发生在播种后一个月左右。附加关键词：半干旱热带，间作，木豆，根系，氮平衡，Osamu ITO et al.：Dynamics of Roots and Nitrogen in Cropping Systems of the Semi-Arid Tropics 35

An agreement was made in 1984 between the Government of Japan (GOJ) and the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) to set up a collaborative research project entitled "Development of Cultivation for Upland Crops in 33 34 JJRCAS ]. No.3, 1996 the Semi-Arid Tropics". Within this framework, scientists in the first phase of the project (1984-1989) concentrated their studies on phosphorus (P) nutrition of grain legumes in the semi arid tropics (SAT). During the second phase of the project (19891994) the scientists focused on the dynamics of roots and nitrogen (N) in cropping systems, particularly in pigeonpea-based intercropping systems. Pigeonpea-based intercropping is widely adopted by resource-poor farmers in the SAT. Highlights of the five year activities are summarized below. Using an exponential fitting of profile distribution of root length, it was found that the roots of pigeonpea spread less to the horizontal direction and more to the vertical direction than those of sorghum, pearl millet, groundnut and cowpea. A model based on weather and soil data predicted that the progression of the rooting front of pigeonpea was more rapid for the same physiological age. A kinetic study on N uptake showed that pigeonpea could utilise soil and fertilizer N as efficiently as other crops which lack an ability of biological nitrogen fixation (BNF), suggesting that there would be a considerable competition for N with other companion crops, such as cereals in intercropping. To reduce the competition for external N it is important to increase the dependency of pigeonpea on BNF. Measurement of root respiration showed that pigeonpea would invest a considerably higher respiratory energy for N uptake. Nitrate (N03-N) concentration in the soil solution extracted by using ceramic porous cups was found to be highest at the beginning of the cropping season and it decreased rapidly thereafter. The N03-N concentration in the soil solution decreased and a zero value was recorded two months after sowing. It was estimated that an amount of between 100-150 kg ha· 1 of mineralized N was detected in the soil solution within a 50 cm soil depth, prior to sowing. This suggests that an appreciable amount of N would be available for crop uptake in nutrient-limited Alfisol during the initial growth stage. The 15 N labelling and 15 N natural abundance studies showed that the N balance sheet among different N sources for the crops, i.e., soil N, fertilizer N and atmospheric N, would be altered by intercropping, toward a larger proportion of N derived from biological nitrogen fixation. The application of urea to the sorghum row was superior to broadcasting and split applications, and delayed application one month after sowing was superior to basal application (before sowing) in terms of nitrogen use efficiency (NUE) of a component sorghum crop, although biomass yield was not affected. The delayed application is advantageous because if crop establishment fails due to insufficient rainfall, no fertilizer cost is incurred. To improve resource utilization in intercropping, it was recommended that pigeonpea be intercropped with a crop which has a shallower root system and a higher N uptake efficiency such as sorghum. In addition, delayed N-fertilization to the cereal crop before N disappears from the soil solution, which normally occurs about one month after sowing, is recommended. Additional key words: semi-arid tropics, intercropping, pigeonpea, root system, nitrogen balance Osamu ITO et al. : Dynamics of Roots and Nitrogen in Cropping Systems of the Semi-Arid Tropics 35

Dynamics of Roots and Nitrogen in Cropping Systems of the Semi-Arid Tropics

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