Effects of cow dung organic fertilizer on sweet sorghum and grass nutrients in karst regions in Chongqing

In order to improve the soil fertility and analysis the digestion and utilization ability of soil-forage system for the cow dung nutrient in the karst regions in Chongqing, we studied the distribution and utilization of N, P, K elements in the soil-sweet sorghum system by applying cow dung into the soil-sweet sorghum system. This research employed different fertilization levels by 1, 2, 3, 4, 5 kg·m-2, and compared with a fertilizer control group and a blank control group. When the cow dung applied with 4 kg·m-2, the ability of soil keeping total nitrogen, total phosphorus were highest with 523.07 mg·kg-1 soil nitrogen and 110.39 mg·kg-1 phosphorus content. When the cow dung applied with 3 kg·m-2, the ability of soil maintaining potassium was highest with 74.5 mg·kg-1 rapidly-available potassium and 4.19 g·kg-1 total potassium content. When the cow dung applied with 3 kg·m-2, sweet sorghum had strongest absorption of total nitrogen which was 313.71 mg·kg-1. When the cow dung applied with 4 kg·m-2, sweet sorghum had strongest absorption of total phosphorus which was 93.00 mg·kg-1. When the cow dung applied with 2 kg·m-2, sweet sorghum had strongest absorption of potassium which was 18.6 mg·kg-1. Sweet sorghum biomass increased firstly and then dropped with the increase of organic fertilizer. When organic fertilizer applied with 4 kg·m-2, sweet sorghum had highest biomass of 132.84 kg. The biomass slightly decreased when more cow dung applied. Based on our research, 3~4 kg·m-2 was the optimal fertilizer rate of the soil-sweet sorghum system.