Effect of different application ratios of chemical and organic fertilizers on soil quality in double cropping paddy fields

ObjectivesA long-term paddy soil quality evolution experiment started from 1984 in Jiangxi Province was conducted to systematically analyze soil quality of double-rice cropping field in red soil region, and acquire the optimum fertilization measures to improve soil quality.

MethodsThe long-term experiment included eight treatments, control (CK, no nutrient input), phosphorus (P) and potassium(K) fertilizer treatment (PK), nitrogen (N) and P fertilizer treatment (NP), N and K fertilizer treatment (NK), N, P and K fertilizer treatment (NPK), 70% chemical fertilizer and 30% organic fertilizer treatment (70F + 30M), 50% chemical fertilizer and 50% organic fertilizer treatment (50F + 50M), and 30% chemical fertilizer and 70% organic fertilizer treatment (30F + 70M). Two soil physical properties (soil bulk density and total porosity), 7 basic chemical properties (organic matter, total N, total P, available N, available P, readily available K and pH) and 3 biological properties (the number of bacteria, fungi and actinomycetes) were determined after the harvest of late rice in 2012. Effects of the long-term fertilization on soil properties were analyzed. Principal component and cluster analysis were used to evaluate the effect of long-term different fertilization systems on soil quality of double-rice cropping field in red soil region.

Results The significant differences of soil properties were founded among the treatments. Compared with the chemical fertilizer treatments, the long-term application of chemical fertilizer and organic manure reduced soil bulk density by 12.7%–20.6%, and increased soil total porosity by 2.3%–17.4%, increased organic matter, total N, available N, total P and available P by 22.5%–41.8%, 9.8%–20.9%, 11.1%–30.3%, 11.1%–71.7% and 131%–175%, respectively. In addition, the soil pH in the treatments of chemical fertilizer combined with organic manure were increased by 0.19–0.48 than those of the chemical fertilizer treatments. The 2 principal components which could reflect 87.4% of the original information were extracted from the initial 12 indices. In the first principal component, organic matter, bulk density, fungi, total nitrogen, available P, actinomycetes, total porosity, bacteria, total P and available N had higher load value, while pH and readily available K had higher load value in the second principal component. The levels of soil quality under different fertilization treatments were sorted as follows: 30F + 70M > 50F + 50M > 70F + 30M > NPK > NP > NK > PK > CK. The soil quality of paddy soil under the long-term different fertilization systems was divided into 4 grades: first grade (30F + 70M), second grade (50F + 50M, 70F + 30M), third grade (NPK, NP), and fourth grade (NK, PK, CK).

ConclusionsThe study suggested that chemical fertilizer combined with organic manure can increase soil nutrient content compared with chemical fertilizer, improve soil physical properties, reduce soil acidification and improve soil microbial counts. Thus, chemical fertilizer combined with organic manure is the most effective fertilization measure to improve the soil quality of double-rice cropping field in red soil region.