Effect of Land Use on Soil Phosphorus Sorption-Desorption Under Intensive Agricultural Practices in Plastic-Film Greenhouses

With rapid urbanization and economic growth, Chinese traditional rice-legume production is increasingly replaced by vegetable and horticultural flower production, which could affect soil properties. This study was conducted near Kunming City, Yunnan Province, Southwest China to investigate how soil phosphorus （P） sorption and desorption processes respond to land use changes and to relate P sorption and desorption parameters to soil properties. Soil samples （0-20, 20-40, 40-60, 60-80 and 80-100 cm） were collected from five sites representing four land use types： rice-legume production in a two-crop, one-year rotation （Rice）, vegetable production in open fields （Vegetable）, recent （〈 3 years） conversion from open fields to plastic-film greenhouse vegetable and flower production at two sites （VFCS1 and VFCS2）, and longer-term （〉 10 years） plastic-film greenhouse vegetable and flower production （VFCL）. The changes in land use affected soil pH, electrical conductivity, available N and P and organic carbon content in topsoil and subsoil. In turn, these changes of soil properties influenced soil P sorption capacity. The P sorption maximum （Smax） was affected by land use types, soil sampling depth and their interactions （P 〈 0.0001）. For surface soil, Smax was in the order of Rice （1 380 mg kg-1） 〉 VFCL （1 154 mg kg-1） 〉 VFCS2 （897 mg kg-1） 〉 VFCS1 （845 mg kg-1） 〉 Vegetable （747 mg kg-1）. The lowest Sm^x generally occurred at the surface （except for Rice at 80-100 cm） and increased with depth. The amount of P desorbed during the 8 successive extractions was in the range 23%-44% of sorbed P, and was not affected by land use types or sampling depths. The decreases in Smax suggested that soil P sorption capacity decreased when rice-legume production converted to more intensive vegetation and flower production and caution should be exercised when applying P fertilizer to minimize potential leaching and runoff P loss to the environment.

Climatic variables: Evaporation, sunshine, relative humidity, soil and air temperature and its adverse effects on cotton production

Cotton yield is a function of growth rates,flower production rates,and flower and boll retention during the fruiting period.Information on the relationship between climatic factors and the cotton plant’s ability to produce and sustain flower buds,flowers,and bolls will allow one to model plant responses to conditions that frequently occur in the field and to predict developmental rate or the formation of these organs.This study investigates the statistical relationship between various climatic factors and overall flower and boll production.Also,the relationship between climatic factors and production of flowers and bolls obtained during the development periods of the flowering and boll stage.Further,predicting effects of climatic factors during different convenient intervals(in days)on cotton flower and boll production compared with daily observations.Evaporation,sunshine duration,relative humidity,surface soil temperature at 1800 h,and maximum air temperature,are the important climatic factors that significantly affect flower and boll production.The five-day interval was found to be more adequately and sensibly related to yield parameters.Evaporation;minimum humidity and sunshine duration were the most effective climatic factors during preceding and succeeding periods on boll production and retention.There was a negative correlation between flower and boll production and either evaporation or sunshine duration,while that correlation with minimum relative humidity was positive.