Quanzhong Huang

Modeling Soil Water Retention Curve with a Fractal Method

ABSTRACT Many empirical models have been developed to describe the soil water retention curve (SWRC). In this study, a fractal model for SWRC was derived with a specially constructed Menger sponge to describe the fractal scaling behavior of soil; relationships were established among the fractal dimension of SWRC, the fractal dimension of soil mass, and soil texture; and the model was used to estimate SWRC with the estimated results being compared to experimental data for verification. The derived fractal model was in a power-law form, similar to the Brooks-Corey and Campbell empirical functions. Experimental data of particle size distribution (PSD), texture, and soil water retention for 10 soils collected at different places in China were used to estimate the fractal dimension of SWRC and the mass fractal dimension. The fractal dimension of SWRC and the mass fractal dimension were linearly related. Also, both of the fractal dimensions were dependent on soil texture, i.e., clay and sand contents. Expressions were proposed to quantify the relationships. Based on the relationships, four methods were used to determine the fractal dimension of SWRC and the model was applied to estimate soil water content at a wide range of tension values. The estimated results compared well with the measured data having relative errors less than 10% for over 60% of the measurements. Thus, this model, estimating the fractal dimension using soil textural data, offered an alternative for predicting SWRC.

Effects of water deficits on growth, yield and water productivity of drip-irrigated onion (Allium cepa L.) in an arid region of Northwest China

Aiming at investigating an appropriate irrigation management strategy that could lead to increase onions yields and improve water productivity (WP), a two-year field experiment was conducted in the arid region of Northwest China with drip irrigation and plastic mulch. Eight treatments were considered: four with different levels of water stress throughout the crop season, and four where water stress was applied at the establishment, development, bulbification and ripening stages. The seasonal actual evapotranspiration (ETa), plant height, above-ground biomass, yield (total, high-quality and marketable quality yields) as well as related irrigation and total water productivity were determined. Plant heights, above-ground biomass and the referred yields have shown to be sensitive to water stress, particularly during the development and bulbification stages. Due to the importance of quality of horticultural products, the WP computed with the yields of high-quality bulbs revealed the most informative contrarily to the WP computed with the total yields. It could be concluded that water stress has to be avoided during the development and bulbification stages, and only small deficits are acceptable if applied throughout the crop season.

Effects of regulated deficit irrigation on yield and water productivity of chili pepper (Capsicum annuum L.) in the arid environment of Northwest China

Due to the scarcity of water resources in Northwest China, the use of deficit irrigation scheduling is beneficial for sustainable agricultural development. Therefore, a 2-year field experiment was performed to investigate the effects of regulated deficit irrigation (RDI) on the yield and water productivity (WP) of drip-irrigated chili pepper plants in a typical arid environment of Northwest China. The results indicate that RDI strategies reduced actual crop evapotranspiration by 2–27%. Crop coefficients for chili pepper averaged 0.85, 1.09 and 0.84 for the development, middle and late stages, respectively. The highest yield occurred under full irrigation. The largest yield reduction (13–20%) was recorded when water deficit occurred during the middle stage. Fifty percent water deficit reduced yields more than 25% water deficit did. The highest irrigation water productivity and WP were achieved when water deficit occurred during the late stage. RDI may improve fruit quality by increasing the content of total soluble solids of the fresh fruit. In conclusion, full irrigation is recommended first for achieving the highest yield, and a water deficit of 25–50% during the late stage is also recommended if considering economic benefits and WP in the study region.