Effect of biochar on the soil nutrients about different grasslands in the Loess Plateau

Serious soil erosion across the Loess Plateau has decreased the concentration of soil nutrients to low levels. Biochar amendments to the soil are an efficient method of improving soil nutrients; however, the effects of biochar amendments on the different soil types in the Loess Plateau are not well understood. In our experiments, we compared the effects of biochar on the soil organic matter, nitrogen and phosphorus content in the Loess Plateau. Four different grasslands abandoned in 1985, 1992, 2000 and 2005 were selected for the experiment. A 3-year field study was conducted in 2 m × 1 m plots to investigate changes in soil nutrient retention caused by biochar amendments at rates of 0 g/kg (control), 4 g/kg, 8 g/kg and 16 g/kg. The 0-40 cm soil profile was collected in layers of 0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm and the soil organic matter, total nitrogen, total phosphorus, ammonium nitrogen and nitrate nitrogen contents were measured after three years of biochar applications. The results showed that biochar amendments resulted in significant improvements to soil organic carbon, nitrate nitrogen and soil total nitrogen. When biochar was added to the 0-20 cm layer at 4 g/kg, 8 g/kg and 16 g/kg, the soil organic carbon content was increased by 2.67 g/kg, 5.34 g/kg and 10.67 g/kg, respectively; soil total nitrogen was increased by 0.24 g/kg, 0.47 g/kg and 0.83 g/kg, respectively; and soil nitrate nitrogen was increased by 0.56 mg/kg, 0.91 mg/kg and 1.63 mg/kg, respectively. Biochar amendments did not show a significant influence on soil ammonium nitrogen in the 0-20 cm soil layer. However, the soil phosphorus content decreased with increasing amounts of biochar, especially at high biochar application rates. These results show that the incorporation of biochar into the soil of the Loess Plateau has the potential to enhance the soil organic carbon and soil nitrogen contents, although it must be used in conjunction with a phosphorus fertilizer.