Influence of biochar application on sandy soil hydraulic properties and nutrient retention

Sustainable agriculture in sandy soil generally faces large constraints due to low water holding and nutrient retention capacity, and accelerated mineralization of soil organic matter. Recent studies have shown that biochar can affect hydraulic properties and nutrient retention in arable soils. However, biochar effects have not been fully studied on sandy soils in drylands. In this study, the effect of biochar on sandy soil hydraulic properties and nutrient (nitrate and phosphorus) retention were investigated. Biochar was generated in the laboratory at three pyrolysis temperatures (300, 400 and 500°C) from black locust (Robinia pseudoacacia L.) collected in Tottori sand dune forest. Three mixing rates of biochar (0, 10 and 20 Mg ha -1 ) were used in the experiment. Biochar amendment improved sandy soil hydraulic properties and nutrient retention. The effect of temperature in function of mixing rate had impact on soil hydraulic properties. It was found that biochar produced at 500°C with 20 Mg ha -1 rate exhibited the highest impact. Application of biochar increased the available water capacity by 97%, saturated water content by 56%, and reduced hydraulic conductivity with increasing moisture content when compared to unamended sand. Nitrate retention was significantly affected by both pyrolysis temperature and mixing rate while only mixing rate affected phosphorus retention. The control soil retained only 1% of the applied nitrate, whereas biochar application increased the soil retention of nitrate up to 23% with 500°C at 10 Mg ha -1 and 37% with 300°C at 20 Mg ha -1 mixing rate. Among treated soils, biochar produced at 500°C and mixed at 20 Mg ha -1 rate had the highest retention of phosphorus while that produced at 400°C and mixed at 10 Mg ha -1 ratio retained the least amount of phosphorus. This study highlights the importance of pyrolysis temperature and mixing rate of biochar on its effect on sandy soil hydraulic properties and nutrient retention and hence, the amendment value of biochar in the sandy soil.