Effect of long-term nutrient management practices on soil health and paddy yield of rice-rice-fallow cropping system in tropic humid climate

Long-term repeated nutrient management practices may have impact on soil health and sustainable paddy (Oryza sativa) production. Therefore, a long-term (33 years) field experiment was conducted at Bangladesh Rice Research Institute in Gazipur with the objective of finding the impact of repeated inorganic and integrated nutrient management (INM) practices on soil biochemical properties, soil quality and its cumulative effect on paddy yield. Experiment was permanently laid out in a replicated complete block design with three replications and modern paddy varieties, BRRI dhan49 and BRRI dhan29, were grown in wet and dry seasons respectively. Treatments imposed were; balanced chemical fertilizer (BCF), K minus from BCF, P minus from BCF, N minus from BCF, Chemical fertilizer with 3 t ha−1 decomposed cowdung (CD), Chemical fertilizer with 2 t ha−1 decomposed poultry litter (PL) and Fertilizer control. The SOC decreased 8% due to 33 years BCF compared to initial soil and increased 18% in INM compared to BCF practice during last 10 years. Long term BCF practices did not bring significant changes in soil pH, however 0.09 units increased and 1.45% bulk density decreased in PL-INM practice. Urease and phosphatase activities, total bacteria, phosphate solubilizing bacteria, free-living N2 fixing bacteria, water stable aggregates, NH4+-N, available P, exchangeable K were increased in INM practices and between two INM treatments, PL was superior over CD. The highest SQI (0.93) and 10 years’ average paddy yield per season (4.99 t ha−1) was obtained in PL-INM followed by CD-INM (SQI, 0.80 and grain yield 4.12 t ha−1) and the lowest in the N minus from BCF practice (SQI, 0.16 and paddy yield 3.2 t ha−1) and control (SQI, 0.33 and paddy yield 2.9 t ha−1) treatment. SQI due BCF practice was 0.68 and average paddy yield was 4.36 t ha−1. The results of AreaSQI revealed that NH4–N, available P and enzyme activities are the most sensitive soil parameters that degraded due to different nutrient management practices. The study also proved that imbalance fertilizer application, especially removal of N nutrition, was the most detrimental for paddy soil quality and PL-INM treatment is the best nutrient management practice for maintenance of soil health in the hyperthermic vertic endoaquepts and tropical humid climate.