Effects of combined application of biogas slurry with chemical fertilizers on fruit qualities of Prunus persica L. and soil nitrogen accumulation risk

The intensive crop production and livestock breeding in China are always accompanied by the production of large amounts of manure and plant residues, not properly managed by farmers, resulting in a considerable threat to environment. Anaerobic digestion has been demonstrated to be an attractive treatment that provides several benefits to improvement of biomass energy and development of recycling agriculture. A two-year field experiment was carried out to study the effects of combined application of anaerobically digested dairy slurry (DS) and water hyacinth slurry (WHS) with chemical fertilizers on fruit production and quality of peach (Prunus persica L.) and accumulation of soil mineral nitrogen. The results show that the combined applications of biogas slurry with chemical fertilizers improve the yield and quality of peach. In the condition of equal amount of nitrogen application, the treatment of 25% N substituted by WHS and 75% N substituted by DS shows the highest contents of soluble solids and sugar. And the rational application rates of the DS and WHS were 200 kg/plant annually. The soil NH+4 concentrations are decreased with the increase of soil depth. Over-substitution of N by biogas slurry (75% and 100%) can cause nitrate accumulation in surface and subsurface soil layers, while the low rate substitutions of N have no significant impacts on nitrate accumulation in surface and subsurface layers. Nitrate mainly is accumulated in the plough pan for the treatments of traditional fertilization (excessive fertilization) and the low N substitution rates by biogas slurry. The nitrate concentrations in subsurface soil layer treated by 25% N substitution by WHS and 50% N substitution by DS are in the safety range of 15 mg/kg, however, further observation and evaluation on the nitrate accumulation in soils will be necessary if long term fertilization by biogas slurry is implemented in the region..