Uneven light distribution and low water holding capacity are two constraints limiting strawberry (Fragaria×ananassa Duch.) production in coastal northern Atlantic areas. A study was conducted in a commercial strawberry production field characterized by rapid internal soil drainage and undulating land features in Nova Scotia. The objectives were to examine the uneven distribution patterns of solar irradiance (IRR), temperature and soil water content (SWC) and quantify correlations of these physical variables with strawberry fruit yield, plant reflectance water index (WI) and leaf chlorophyll. Strawberry row orientation was along the field aspect in the north-south (N-S) direction for maximizing plant sunlight exposure and spring rainfall drainage. The measurement design consisted of a nested grid with five transects. Results showed that solar radiation incident upon the canopy was significantly higher (mean IRR 779-820Wm-2) in the shoulder and slope areas compared to the mean IRR of 709Wm-2 in downslope area (P<0.001), where higher SWC and lower temperature stimulated strawberry fruit bearing. Significantly higher reflectance WI was related to low strawberry yield (R2=0.55, P<0.05). Strawberry fruit yield was positively correlated to normalized difference vegetation index, ratio nitrogen vegetative index and leaf chlorophyll (0.46<R2<0.61, P<0.05). Distribution patterns and correlations between strawberry fruit yield and physical variables suggested that IRR and water stress occurring with the influence of high topographic features resulted in reduced strawberry fruit bearing ability. It was suggested that the N-S row orientation along the aspect would help sunlight capture but not water holding for strawberry plant fruit bearing needs. A new planting design for alternative orientation of rows (NE-SW or W-E) and drip irrigation should be tested for light and water management in soils with natural constraints.

Statistical analysis of the heterogeneity of soil bulk density in regional scale is important tocrop growth and tillage management. While most field data focus on bulk density up to a depth of 0.3 m, this study measured the bulk density of 28 in situ soil core locations up to a depth of 1.3 m. Geostatistical method was used to analyze the anisotropic spatial variability and three-dimensional Sequential Gaussian Simulation (SGSIM) was conducted. The results of nugget/sill ratio indicated that the sampling scheme was fine enough to capture the spatial correlation distance of bulk density in the vertical direction. The nugget effect, however, in the horizontal direction suggested that the sampling frequency was not enough for bulk density in that direction. The result of three-dimensional SGSIM is consistent with measured data, indicating that the simulation method is suitable for this research objective. The results may provide basic information for other agricultural management practices.

Understanding the distribution of alluvial soil textures on a large scale is crucial for agricultural and environmental management. In our study an indicator variogram and a sequence indicator simulation (SIS) algorithm were used to analyze and simulate the spatial distribution of soil textures based on observations of 139 soil profiles in a 15km2 region in the Huabei alluvial plain in China. The nugget-to-sill ratio value (SH) of the indicator variograms for all textures in a vertical direction (Z) was equal to 1. This suggests that spatial auto-correlation dominates in the direction of sedimentary deposition with 0.05 m sampling intervals. In contrast, SH ratios from 0.48 to 0.81 show that the soil textures have a degree of randomness in the horizontal direction (X, Y) where the sampling distance was about 300 m. Using the indicator variograms in 3 directions (X, Y and Z) as outlined above, a 3D SIS algorithm was used to simulate textures. Finally, the simulation results were evaluated by the reproduction of a histogram, variogram and the mean absolute error (MAE) of prediction. The mean absolute percentage error (MAPE) of the histogram reproduction showed that the main textures (sand, sandy loam and clay) were described well, whereas the less prevalent textures were underestimated. The MAPE of the indicator variograms reproduction were reasonable although some deviation existed as less prevalent textures in the vertical direction. The mean absolute error (MAE) of the SIS prediction was 0.47. This result is considered acceptable for a category variable because of the stochastic nature of soil textures in a horizontal direction, and hence may provide useful data for other agricultural research.

Excessive irrigation and nitrogen applications result in substantial nitrate leaching into groundwater in intensively cropped oases in desert areas of Alxa, Inner Mongolia. An integrated modelling approach was developed and applied to compare policy incentives to reduce nitrate leaching. The integrated model consists of a process-based biophysicalmodel, a meta-model, a farm economic model and an assessment of policy incentives. The modelling results show that there are "win-win" opportunities for improving farm profitability and reducing nitrate leaching. We found that 4471 Yuan ha 1 of farm gross margin could be obtained with a reduction in nitrate leaching of 373 kg ha 1. Farmers' lack of knowledge about water and nitrogen in soil, and on crop requirements for water and nitrogen could explain the differences, so that agricultural extension is an appropriate policy incentive for this area. When the economic optimumis obtained reductions in nitrate leaching are not achievable without profit penalties and there is a "trade-off" relationship between farm profitability and groundwater quality protection. The combination of low elasticity of nitrate leaching and large elasticity of farm gross margin against water price increases results in very high costs for reducing nitrate leaching (105.6 Yuan kg 1). It is suggested that if the water price increases were coupled with subsidies for adopting nitrate leaching mitigation practices, environmental gains could come at a lower cost.

Water scarcity and nitrate contamination in groundwater are serious problems in desert oases in Northwest China. Field and 15N microplot experiments with traditional and improved water and nitrogen management were conducted in a desert oasis in Inner Mongolia Autonomous Region. Water movement, nitrogen transport and crop growth were simulated by the soil-plant system with water and solute transport model (SPWS). The model simulation results, including the water content and nitrate concentration in the soil profile, leaf area index, dry matter weight, crop N uptake and grain yield, were all in good agreement with the field measurements. The water and nitrogen use efficiency of the improved treatment were better than those of the traditional treatment. The water and nitrogen use efficiency under the traditional treatment were 2.0 kg m-3 and 21 kg kg-1, respectively, while under the improved treatment, they were 2.2 kg m-3 and 26 kg kg-1, respectively. Water drainage accounted for 24-35% of total water input (rainfall and irrigation) for the two treatments. Nitrogen loss by ammonia volatilization and denitrification was less than 5% of the total N input (including the N comes from irrigation). However, 32-61% of total nitrogen input was lost through nitrate leaching, which agreed with the 15N isotopic result. It is impetrative to improve the water and nitrogen management in the desert oasis.