Effect of bentonite amendment on soil hydraulic parameters and millet crop performance in a semi-arid region

We evaluated the effect of bentonite soil amendments on soil moisture, soil water storage, soil saturated hydraulic conductivity, water use efficiency and yield of millet in a field experiment in a sandy loam soil in a semi-arid region in northern China from 2011 to 2015. Treatments included six rates of bentonite amendments (0, 6, 12, 18, 24 and 30 Mg/ha) applied only in the first year. Adding bentonite amendments increased soil moisture, soil water storage and saturated hydraulic conductivity in the 0-60 cm layer. All bentonite amendments significantly (P < 0.05) increased above-ground biomass and grain yield, and improved water use efficiency in all five years. Above-ground biomass increases ranged from 2% to 39%, grain yield increases ranged from 3% to 20%, and water use efficiency increases ranged from 0% to 29%. The treatment with 24 Mg/ha bentonite had the greatest effect averaged over five years; the maximum bentonite rate treatment with 30 Mg/ha showed the greatest effect in the fifth year of the experiment. The treatment with 18 Mg/ha had the highest economic return over five years. Bentonite amendments show promise for improving soil water-holding capacity and crop yield in a semi-arid region, and therefore deserve further study.