Water-stable aggregates and aggregate-associated organic carbon and nitrogen after three annual applications of poultry manure and spent mushroom wastes

Water stable aggregates influence mechanisms for both water and fertility conservation and nutrient release in the soil. The effect of application of different organic amendments on aggregate stability and carbon-nitrogen storage within aggregates of a degraded soil was studied. The treatments were: control (P0S0), no amendments, 5 t ha−1 poultry manure (P5S0), 10 t ha−1 poultry manure (P10S0), 5 t ha−1 spent mushroom waste (P0S5), 10 t ha−1 spent mushroom waste (P0S10) and 5 t ha−1 each of poultry manure and spent mushroom waste (P5S5) applied in three consecutive years. These were arranged in randomized complete block design in five replicates. Soil samples were collected from the topsoil (0-20 cm), air-dried and separated into 4.75-2.0, 2.0-1.0, 1.0-0.5, 0.5-0.25, and <0.25 mm aggregate classes by dry sieving. Results showed that P5S5 increased macro aggregates >0.25 mm and mean weight diameter (MWD) over other treatments. Saturated hydraulic conductivities (Ksat) were 17.55 cm hr−1 and 16.28 cm hr−1 in P5S0 and P0S10 amended soils, respectively. Generally, spent mushroom waste (SMW) and poultry manure (PM) significantly (p < 0.05) reduced bulk density and increased total porosity, indicating positive effects of SMW and PM as soil amendments. Total nitrogen (N) concentrations in aggregate classes were significantly higher in soils amended with PM and SMW than the control. The P10S0 treatment had the highest concentrations of N (1.51 g kg−1) in 1.0-0.5 mm aggregates size class. Soil organic carbon (SOC) was preferentially higher in larger aggregates >2 mm and in smaller aggregates <0.25 mm irrespective of treatments, whereas, total N was higher in aggregates >0.5 mm in PM amended soils. In all the treatments, SOC was enriched in larger aggregates than smaller aggregates. Poultry manure improved soil structure, aggregate-associated OC and total N than SMW. However, SMW has the potentials for use as soil amendment because it showed positive effects on soil structure and soil C-N storage.