Managing precipitation use in sustainable dryland agroecosystems
Managing precipitation use in sustainable dryland agroecosystems
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DOI：
10.1111/j.1744-7348.2004.tb00326.x
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发表时间：
2004-04
影响因子：
2.6
通讯作者：
Gary A. Peterson;D. Westfall
中科院分区：
文献类型：
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作者：
Gary A. Peterson;D. Westfall
在北美大平原，一年中大部分月份的潜在蒸发量都超过了降水量。每年约75%的降水来自4月至9月，并伴有高温和低相对湿度。大平原的旱地农业一直依赖于小麦休耕农业生态系统中的小麦生产（一个作物年接着一个休耕年）。从历史上看，该系统在休耕期间使用机械杂草控制措施，基本上没有作物残留物覆盖，以防止土壤侵蚀，并大大加速土壤有机碳氧化。本文综述了北美大平原降水管理的进展，并综合了现有长期试验的数据来论证所涉及的管理原则。1985年建立了长期试验，以确定旱地作物和土壤管理系统，这些系统将最大限度地提高降水利用效率（每单位降水生物量产量最大化），提高土壤生产力，并增加大平原中西部农民的经济回报。在主要目标中包含了侧重于减少夏季休耕时间和扭转小麦-休耕种植系统中发生的土壤退化的子目标。实验包括四个变量：1)气候状况；2)土壤;3)管理制度；4)时间。气候变量基于潜在蒸散（ET）的三个水平，由科罗拉多州东部的三个地点代表。所有站点的年长期平均降水量约为400-450 mm，但在生长季节，开口蒸发皿蒸发量从北部的1600 mm到南部的1975 mm不等。土壤变量由每个站点的土壤链线序列表示。管理制度（第三个变量）在夏季休耕时间长短上有所不同，并强调增加作物多样性。所有系统都采用免耕技术进行管理。第四个变量是时间，本文给出的结果是针对前12年（4年制系统的3个周期）。比较不同周期长度的种植系统和包含休耕期（不生产作物）的种植系统的产量，使用一种称为年化的技术。产量是通过将系统中所有作物的产量总和除以系统周期的总年数来计算的。例如，在小麦休耕系统中，小麦产量除以2，因为生产一种作物需要2年的时间。与休耕小麦相比，种植制度集约化使粮食和作物残茬年化产量提高了75%至100%。与休耕小麦相比，农民的净收益增加了25%至45%。与小麦休耕制度相比，集约化种植制度在12年后分别使土壤有机碳含量增加875和1400公斤公顷。所有种植制度的影响都独立于气候和土壤梯度，这意味着在所有气候和土壤组合中都存在碳固存的潜力。土壤碳含量的增加与作物残渣碳的还田量直接相关。大团聚体的改善也与团聚体中C含量的增加有关。每添加1000 kg ha -1，土壤容重降低0.01g cm -3，每添加1000 kg ha -1，土壤有效孔隙度提高0.3%。免耕做法使种植集约化程度超越传统的小麦休耕系统成为可能，从而使中西部大平原农业生态系统的水资源利用效率提高了30%。种植集约化还通过增加作物残茬返回土壤的数量，为土壤生产力提供了正反馈。
In the Great Plains of North America potential evaporation exceeds precipitation during most months of the year. About 75% of the annual precipitation is received from April through September, and is accompanied by high temperatures and low relative humidity. Dryland agriculture in the Great Plains has depended on wheat production in a wheat-fallow agroecosystem (one crop year followed by a fallow year). Historically this system has used mechanical weed control practices during the fallow period, which leaves essentially no crop residue cover for protection against soil erosion and greatly accelerates soil organic carbon oxidation. This paper reviews the progress made in precipitation management in the North American Great Plains and synthesises data from an existing long-term experiment to demonstrate the management principles involved. The long-term experiment was established in 1985 to identify dryland crop and soil management systems that would maximize precipitation use efficiency (maximization of biomass production per unit of precipitation received), improve soil productivity, and increase economic return to the farmers in the West Central portion of the Great Plains. Embedded within the primary objective are sub-objectives that focus on reducing the amount of summer fallow time and reversing the soil degradation that has occurred in the wheat-fallow cropping system. The experiment consists of four variables: 1) Climate regime; 2) Soils; 3) Management systems; and 4) Time. The climate variable is based on three levels of potential evapotranspiration (ET), which are represented by three sites in eastern Colorado. All sites have annual long-term precipitation averages of approximately 400-450 mm, but vary in growing season open pan evaporation from 1600 mm in the north to 1975 mm in the south. The soil variable is represented by a catenary sequence of soils at each site. Management systems, the third variable, differ in the amount of summer fallow time and emphasize increased crop diversity. All systems are managed with no-till techniques. The fourth variable is time, and the results presented in this paper are for the first 12 yr (3 cycles of the 4-yr system). Comparing yields of cropping systems that differ in cycle length and systems that contain fallow periods, when no crop is produced, is done with a technique called annualisation. Yields are annualised by summing yields for all crops in the system and dividing by the total number of years in the system cycle. For example in a wheat-fallow system the wheat yield is divided by two because it takes 2 yr to produce one crop. Cropping system intensification increased annualised grain and crop residue yields by 75 to 100% compared to wheat-fallow. Net return to farmers increased by 25% to 45% compared to wheat-fallow. Intensified cropping systems increased soil organic C content by 875 and 1400 kg ha', respectively, after 12 yr compared to the wheat-fallow system. All cropping system effects were independent of climate and soil gradients, meaning that the potential for C sequestration exists in all combinations of climates and soils. Soil C gains were directly correlated to the amount of crop residue C returned to the soil. Improved macroaggregation was also associated with increases in the C content of the aggregates. Soil bulk density was reduced by 0.01g cm -3 for each 1000 kg ha -1 of residue addition over the 12-yr period, and each 1000 kg ha -1 of residue addition increased effective porosity by 0.3%. No-till practices have made it possible to increase cropping intensification beyond the traditional wheat-fallow system and in turn water-use efficiency has increased by 30% in West Central Great Plains agroecosystems. Cropping intensification has also provided positive feedbacks to soil productivity via the increased amounts of crop residue being returned to the soil.