Crop Yield, N Uptake and Nitrates in a Fluvo-Aquic Soil Profile

The effects of different chemical fertilizer combinations (N, P and K) on crop yield, N uptake and nitrate distribution and accumulation to a depth of 100 cm were studied in a cinnamon fluvo-aquic soil profile (Beijing) with a continuous winter wheat-summer maize cropping system for nine years. The experiment consisted of 7 treatments: no fertilizer control (CK); N alone, N in combination with K (NK), P (NP), and P and K (NPK and N1PK); and P and K in combination without N (PK). The rate of N was 150 kg ha^-1 for the N treatments except Treatment N1PK with higher N rate (195 kg ha^-1), and the rates of P (P₂O₅) and K (K₂O) were 75 and 37.5 kg ha^-1, respectively. The applications of N combined with P and K (NK, NP and NPK) resulted in higher crop yields than a single application of N. The yields followed the order: NPK > NP > N1PK > PK > NK > N > CK for winter wheat, and NPK > N1PK > NP > NK > N > PK > CK for summer maize. Supplement of N with P or K, or both P and K resulted in a higher average N uptake of the two crops, which was in a decreasing order NPK > NP > N1PK > NK > N > PK > CK. The combinations also increased apparent N recovery more than N alone and CK. The nitrate content in the profile was thus reduced more in the combination treatments. The nitrate accumulation in the soil profiles followed the order: N > NK > N1PK > NPK > NP > CK > PK. Higher N uptake by the adequately fertilized crops (Treatment NPK) reduced nitrate accumulation in the profile and thus reduced nitrate leaching. The optimum N:P:K ratio was thus of paramount importance in increasing yields and N uptake of crops and reducing nitrate leaching losses.