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首页> 外文期刊>Geoderma: An International Journal of Soil Science >Inorganic nitrogen dynamics in fallows and maize on an Oxisol and Alfisolin the highlands of Kenya
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Inorganic nitrogen dynamics in fallows and maize on an Oxisol and Alfisolin the highlands of Kenya

机译：肯尼亚高地上Oxisol和Alfisolin上休耕地和玉米中的无机氮动态

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Fallows with naturally regenerated or planted vegetation are important in many subsistence agricultural systems of tropical regions, but the underlying soil processes in fallows are not properly understood. We investigated N dynamics under different fallow vegetation on a Kandiudalfic Eutrudox (2372-mm rain in 16 months) and a Kandic Paleustalf (1266-mm rain in 15 months) in the Kenyan highlands. The treatments, which extended for three cropping seasons (15-16 months), were Zea mays (maize), natural regrowth of vegetation (natural fallow), planted Sesbania sesban (sesbania fallow) and uncultivated soil without vegetation (bare fallow), Inorganic N (nitrate + ammonium-N) to 2-m depth under bare fallow increased by 242 kg N ha(-1) year(-1) on the Oxisol and 54 kg N ha(-1) year(-1) on the Alfisol, indicating that N mineralization exceeded N losses. Subsoil inorganic N (0.5-2.0 m) remained relatively unchanged after three crops of unfertilized maize, which produced limited total biomass because of P deficiency. Inorganic N decreased during natural and sesbania fallows, and both fallows similarly depleted subsoil inorganic N. The fallows depleted inorganic N at 0.5-2.0 m by 75-125 kg N ha(-1) year(-1) down to a minimum N content between 40 and 80 kg N ha(-1). After slashing sesbania and incorporating the above-ground biomass with 154-164 kg N ha(-1), soil inorganic N increased within 2 months by 136 kg N ha(-1) on the Oxisol and 148 kg N ha(-1) on the Alfisol. Inorganic N decreased after cropping the bare fallow on the Oxisol with maize, indicating that inorganic N was prone to leaching during heavy rains when the maize was small. A considerable part of the N in biomass of the natural fallow was recycled. Much of the total N accumulated by the sesbania fallow was removed with the wood and the amount of N recycled was similar an the Oxisol and Alfisol. We conclude that sesbania fallows can retrieve considerable subsoil inorganic N on deep soils with high subsoil N and effectively cycle this N through its rapidly decomposable biomass to subsequent crops.
机译：在热带地区许多自给自足的农业系统中，具有自然再生或种植植物的休耕植物很重要，但是人们对休闲土地的潜在土壤过程却知之甚少。我们调查了肯尼亚高地的Kandiudalfic Eutrudox（16个月降雨量为2372毫米）和Kandic Paleustalf（15个月降雨量为1266毫米）不同休耕植被下的N动态。这些处理方法延长了三个种植季节（15-16个月），包括玉米（Zea mays）（玉米），植被的自然生长（自然休耕），塞斯巴尼亚（Sesbania sesban）耕种（sesbania休闲）和无植被的未耕种土壤（裸休），无机在裸露休耕下，N（硝酸盐+铵态氮）至2 m的深度在Oxisol上增加了242 kg N ha（-1）年（-1），在Oxisol上增加了54 kg N ha（-1）年（-1）。 Alfisol，表明氮矿化超过了N的损失。三种未施肥的玉米作物后，土壤下部的无机氮（0.5-2.0 m）相对保持不变，由于缺磷，总生物量有限。在自然休耕和芝麻休耕期间，无机氮减少，并且两个休耕土壤中的无机氮含量均以同样的方式减少。在0.5-2.0 m时，耕作土壤中的无机氮减少了75-125 kg N ha（-1）年（-1），降至最低氮含量40至80千克N ha（-1）之间。砍掉芝麻种子后，将地上生物量掺入154-164 kg N ha（-1），土壤无机氮在2个月内增加了136 kg N ha（-1）和148 kg N ha（-1）。在Alfisol上。玉米在裸露的土壤上种植玉米后，无机氮下降，这说明玉米小时，大雨时无机氮易于浸出。天然休耕生物量中相当一部分氮被回收。芝麻木中积累的大部分N随木材去除，回收的N量与Oxisol和Alfisol相似。我们得出的结论是，Sesbania休闲可以在深层土壤中吸收大量的N，而这些土壤中的N含量较高，而N则通过其快速分解的生物量有效地循环到后续作物。

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