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291.
Yield constraint analysis for rainfed rice at a research station gives insight into the relative role of occurring yield-limiting factors. However, soil nutrient status and water conditions along toposequences in rainfed farmers’ fields may differ from those at the research station. Therefore, yield constraints need to be analyzed in farmers’ fields in order to design management strategies to increase yield and yield stability.We applied production ecological concepts to analyze yield-limiting factors (water, N) on rice yields along toposequences in farmers’ fields using data from on-farm experiments conducted in 2000-2002 in Indonesia. Potential, water-limited, and N-limited yields were simulated using the ORYZA2000 crop growth model. Farmers’ fields showed large spatial and temporal variation in hydrology (354-1235 mm seasonal rainfall, −150 to 50 cm field-water depth) and fertilizer doses (76-166 N, 0-45 P, and 0-51 kg K ha−1). Farmers’ yields ranged from 0.32 to 5.88 Mg ha−1. The range in yield gap caused by water limitations was 0-28% and that caused by N limitations 35-63%, with large temporal and spatial variability.The relative limitations of water and N in farmers’ fields varied strongly among villages in rainfed rice areas and toposequence positions, with yield gaps due to water and N at the top and upper middle positions higher than at the lower middle and bottom toposequence positions, and yield gaps in late wet seasons higher than those in early wet seasons. Management options (e.g. crop establishment dates, shortening turnaround time, using varieties with shorter duration, supplemental irrigation) to help the late-season crop escape, or minimize the negative effects of, late-season droughts and supplying adequate N-fertilizer are important for increasing yield in rainfed lowland rice in Indonesia. More N-fertilizer should be given to upper toposequence positions than to lower positions because the former had a lower indigenous nutrient supply and hence a better response to N-fertilizer inputs. Systems approaches using production ecological concepts can be applied in yield constraint analysis for indentifying management strategies to increase yield and yield stability in farmers’ fields in other rainfed lowland areas. 相似文献
292.
尕海沼泽化草甸湿地不同地下水位土壤理化特征的比较分析 总被引:3,自引:0,他引:3
为了研究地下水位与土壤理化性质之间的关系,依据自然原因和地形原因形成的水位梯度,对尕海沼泽化草甸湿地区内高水位(SI)、中间水位(SⅡ)和低水位(SⅢ)的土壤理化性质进行了研究。结果表明:尕海沼泽化草甸湿地随着地下水位的降低,土壤颗粒组成中细砂(<0.2 mm)比例下降,粗砂(2~0.2 mm)含量增加,土壤容重显著升高,且土壤容重随土层深度的增加而增大。SI样地平均土壤总孔隙度、最大持水量分别是SⅡ样地的1.19和1.36倍、SⅢ样地的1.93和2.75倍。尕海湿地SI土壤有机碳、全氮、全磷含量比SⅡ和SⅢ分别高出了86.87%和167.35%、99.88%和115.95%、22.32%和58.97%,地下水位的降低显著影响了有机质的分解转化,加快了氧化分解的速率,造成土壤养分(碳、氮、磷)含量的减少,使得湿地土壤环境恶化。 相似文献
293.
利用YE0-KAL612水质分析仪观测数据,统计了莱州市地下水质的地下水位深度、酸碱度、盐度、温度四要素的正常年份变化,并将地下水质四要素与测站同期的降水量、降水强度、大气温度、地面温度进行了对比分析,找出其间的相应关系。结果表明,对正常年份来说,莱州市地下水的温度相对稳定,其变值与降水无显著关系,地下水的最低温度、年中最大变温值均不随大气温度、深层地温的规律变化;强降水造成的地表水径流为影响地下水p H变化的主要因素,因强降水引发的地表径流致酸性物质累积影响地下水p H呈强酸性;地下水的最低水位与降水负距平呈正相关,最高水位受当地灌溉需求量的影响甚大;盐度变化的大小与降水量、降水时空分布是否均匀均呈相关性。 相似文献
294.
综合前人的研究成果,特别是总结近年来国内外学者提出或改进的模型,提出4项建立指标体系的基本原则,即重要性、独立性、差异性和可操作性。并举例说明其应用,证明该原则有助于评价区域内地下水脆弱性。 相似文献
295.
农业节水措施对地下水涵养的作用及其敏感性分析 总被引:1,自引:0,他引:1
以北京市大兴区为研究区,利用经校验的水平衡模型,通过调整灌溉满足率和灌溉水利用系数,探讨了不同农业节水措施对增加地下水补给量和减少地下水开采量的作用及其敏感性。结果表明,不同水文年型下,降低灌溉满足率及提高灌溉水利用系数都能减少地下水开采量,且降低灌溉满足率对减少地下净开采量的作用更为显著,有利于区域地下水涵养。在参数取值范围内,地下水净开采量对灌溉满足率的敏感性较大,而地下水补给量对灌溉水利用系数的敏感性较高。与提高灌溉水利用系数相比,对资源性缺水区域,采用先进节水技术,适度降低区域灌溉满足率,对促进水资源持续有效利用及加大地下水涵养具有更显著的效果。 相似文献
296.
297.
298.
Applying high rates of nitrogen (N) fertilizer to crops has two major disadvantages: (1) the low N fertilizer use efficiency and (2) the loss of N by leaching, which may cause groundwater nitrate (NO3−) pollution, especially in humid areas.The objectives of this study were to adjust and validate the LEACH-W model simulations with data observed in the field; to quantify nitrate concentrations in the soil solution; to estimate N loss by leaching; and to determine the moments during the year when greatest nitrate transport events occur beyond the rooting profile.A randomized complete block design with four replications was established on a typic Argiudoll. Crop fertilization treatments consisted of three N rates (0, 100, and 200 kg N ha−1) using urea and ammonium nitrate solution (UAN) as the N source. Corn (Zea mays L.) was planted and ceramic soil-water suction samplers were installed to depths of 1, 1.5 and 2 m. Drainage was estimated by the LEACH-W model, which adjusted very well the actual volume of water in the soil profile. Nitrogen losses were statistically analyzed as repeated measure data, using the PROC MIXED procedure.Losses of nitrate-nitrogen (NO3−-N) during the study increased as the rate of N applied increased. At all depths studied, statistically significant higher values were found for 200 N compared to 100 N and 0 N, and for 100 N compared to 0 N (p < 0.001).The greatest NO3−-N losses through leaching occurred during crop growth. Significant differences (p < 0.05) were found between cropping and fallow in the three treatments and depths studied for seasons 4 and 5; these two seasons produced the highest drainage volumes at all depths. 相似文献
299.
Effects of wastewater irrigation on soil sodicity and nutrient leaching in calcareous soils 总被引:2,自引:0,他引:2
Soil column studies were conducted with two soils to assess the effects of irrigation with wastewater on soil and groundwater quality. Upon the application of wastewater, exchange occurred between solution sodium (Na+) and exchangeable cations (Ca2+, Mg2+, K+), whereby these cations were released into solution. The average exchangeable sodium percentage (ESP) of the soils increased during leaching from 9 to 21 and 28.8 to 29.7 after applying 5.0 and 3.5 l (about 7 and 6 pore volumes) of wastewater to the soils columns, respectively. Adverse effect of high Na+ concentration in the wastewater on raising ESP was less pronounced in the soil having initial high ESP than in the soil with low initial ESP. Salinity of the soils was also increased with the application of wastewater and Mg2+ and K+ were leached from the soils. These losses would be more severe on soils having a low cation exchange capacity and if, uncorrected could lead eventually to their deficiencies for plant growth. When the soil columns were leached with distilled water the flow rate of one soil decreased to zero after 2.2 pore volume indicating damage to soil structure. Irrigation with wastewater, which is generally more sodic and saline than regional groundwater, increases the rate of soil sodification of shallow groundwater. A relatively simple chromatographic model was used to estimate final ESP profiles in the soils assuming the condition of local equilibrium. This approach had a limited success for one of the soil. Since the final leached concentrations are in good agreement with those of wastewater, we attribute these differences to non-uniform flow through the column. In terms of practical soil and water management, our study reveals that relatively simple means can be useful to predict the water quality in soils, their discharge to ground water, and the hazard of soil structure deterioration. 相似文献
300.