福建省长汀县河田盆地区近35年来地表裸土变化的遥感时空分析

福建省长汀县河田盆地区是中国南方最典型的红壤水土流失区之一,当地人民和各级政府一直为治理该区的水土流失进行着不懈的努力.利用遥感技术对该区1976年以来地表裸土分布的时空变化进行了分析,基于所提出的双重遥感指数法对该区的裸土信息进行提取,查明了该区地表裸土分布的时空变化情况.研究表明,该区近35年的治理已大大减轻了地表的裸露程度,地表裸土面积从1976年的159.17 km2锐减到2010年的51.98 km2.在3个不同的观察时间段里,裸土面积的变化呈现逐次减少、减速加快的趋势,客观地反映了该区水土流失治理的3个重要历史时期和政策所产生的效应.  

宁夏设施番茄连年高强度种植下对土壤特性的影响

通过设施连作高强度种植与开放和半开放式的大田和阳畦种植模式相比较,探究设施土壤连作模式下,土壤养分、重金属、微量元素以及微生物区系组成变化,明确连作模式对土壤细菌和真菌群落多样性以及土壤中细菌真菌优势菌群的影响。结果表明,连作高强度种植条件下土壤中各种离子含量发生了很大的变化,其中温室钠离子和氯离子含量与大田和阳畦地相比有所降低,而钾离子、钙离子和碳酸氢根离子含量相比大田和阳畦地增高。温室连年高强度的种植使土壤微生物数量明显高于大田和阳畦地土壤中微生物的数量,连年种植对土壤微生物影响也比较明显,降低了细菌群落多样性而提高了真菌群落多样性,温室高强度的种植降低了土壤蛋白酶、脲酶和蔗糖酶活性,提高了土壤脱氢酶的活性。温室高强度的种植导致土壤养分的大量积累,尤其是磷素的积累更为严重;对土壤中重金属含量的影响也比较明显,其中对铬和汞的含量影响最大。同时,温室土壤中有效铜和有效锌含量高出阳畦地和大田10倍以上。因此,设施种植要减少连作,合理的轮作使设施土壤长期有效的发展。  

Spatial and Temporal Variability of Sorghum Grain Yield: Influence of Soil,Water, Pests,and Diseases Relationships

This study was conducted to determine relationships between biotic and abiotic factors and to generate information needed to improve the management of site-specific farming (SSF). The effects of water (80% evapotranspiration (ET) and 50% ET), hybrid (drought-tolerant and -susceptible), elevation, soil texture, soil NO₃--N, soil pH, and greenbugs (Schizaphis graminum) (Gb) on sorghum grain yield were investigated at Halfway, TX on geo-referenced locations on a 30-m grid in 1997, 1998, and 1999. Grain yields were influenced by interrelationships among many factors. Grain yields were consistently high under 80% ET treatment and in the upper slopes where the clay and silt fractions of the soil were high. Soil NO₃--N, rainfall, hybrid, and Gb effects on grain yields were seasonally unstable. Soil NO₃--N increased grain yield when water was abundant and depressed grain yields when water was limiting. Plant density effects on grain yield were confounded with hybrid responses to drought and Gb infestation. Managing seasonally unstable factors is a major challenge for farmers and better ways to monitor crop growth and diagnose causes of poor plant growth are needed. To improve the management of SSF, effects of the relationships between biotic and abiotic factors on crop yield must be integrated and evaluated as a system. Based on our study, information on seasonally stable factors like elevation and soil texture is useful in identifying management zones for water and fertilizer application. Water and fertilizers management should be complemented by in-season management of seasonally unstable factors like soil NO₃--N, rainfall, hybrid, and Gb effects on grain yield.  

Spatial and Temporal Variability of Corn Grain Yield: Site-Specific Relationships of Biotic and Abiotic Factors

Inadequate information on factors affecting crop yield variability has contributed to the slow adoption of site-specific farming (SSF). This study was conducted to determine the effects of biotic and abiotic factors on the spatial and temporal variability of irrigated corn grain yields and to derive information useful for SSF. The effects of water (80% evapotranspiration (ET) and 50% ET), hybrid (drought-tolerant and -susceptible), elevation, soil index (SI)(texture), soil NO₃–N, arthropods, and diseases on corn grain yield were investigated at Halfway, TX on geo-referenced locations. Grain yields were influenced by interrelationships among biotic and abiotic factors. Grain yields were consistently high under high water treatment, at higher elevations, and on soils with high SI (high clay and silt). Soil NO₃–N increased grain yields when water was adequate. Management zones for variable rate fertilizer and water application should, therefore, be based on information on elevation, SI, and soil NO₃–N. The effects of arthropods, diseases, and crop stress (due to drought and N) on corn grain yield were unpredictable. Spider mite (Oligonychus pratensis) and common smut (Ustilago zeae) damage occurred under hot and dry conditions in 1998. Spider mite infestations were high in areas with high soil NO₃–N. Moderate air temperatures and high relative humidity in 1999 favored southwestern corn borer (Diatraea grandiosella) and common rust (Puccinia maydis) incidences. Knowledge of conditions that favor arthropods and diseases outbreak and crop stress can improve the efficiency of scouting and in-season management of SSF. Management of SSF can be improved when effects of biotic and abiotic factors on grain yield are integrated and evaluated as a system.