Application of organic amendments to restore soil health and productivity of a degraded soil.

Organic amendments (OAs) have the capacity to enhance physical, chemical, biological soil quality indicators (SQIs) and to improve soil productivity. This study investigated the effects of different OAs (Mushroom Compost, MC; PAS-100 compost, PAS; Anaerobic Digestate Solid Waste, AD_SW; and Poultry Manure, PM), applied at 10 t ha⁻¹ and 30 t ha⁻¹ with or without inorganic fertilizer (applied at 50% of the RB209 recommended rates for maize) on key SQIs, soil health and plant performance on a degraded sandy loam soil. The treatments were laid out in a greenhouse using a completely randomized design and replicated four times. The soil and OAs were thoroughly mixed and incubated for two weeks. Thereafter, composite 3-point soil samples were taken from each treatment replicate for post-incubation (POI) soil analysis. Maize (Zea mays, Severus variety), was used to assess the impact of the OAs on plant performance. Plant height, number of plant leaves and stem diameter were measured weekly. Post-harvest (POH) composite 3-point soil samples were again taken for soil analysis. The data generated from POI and POH laboratory analyses and plant measurements were subjected to analysis of variance (ANOVA) followed by post-hoc Fisher LSD analysis at 5% probability level. At POI, the OAs had 22-44.5% higher water holding capacity [WHC], increased porosity and reduced bulk density [BD] as compared with the un-amended control treatment (CNF). The results indicate that 1% increase in soil organic matter (SOM) increased the Available Water Content (AWC) by 5.31 g g⁻¹ while reducing the BD by 1 g cm⁻¹ and increasing the soil Water Content at Field Capacity (WCFC) by 36.5 g g⁻¹ . The Olsen-P, Available-K, Available-Mg, Total-N, and microbial biomass C [MBC] associated with the OA treatments were significantly higher as compared with CNF treatment. At POH, across application rates, OA treatments with or without inorganic fertilizer addition had >15% higher (p <0.05) WHC [WCFC], 40% higher porosity and 55% lower BD as compared with CNF treatment. For both POI and POH, higher rates (30 t ha⁻¹ ) of OAs with or without inorganic fertilizer addition had higher (p <0.05) effects on the water release characteristics [WCFC, EAW, AWC] than lower (10 t ha⁻¹ ) rates of OAs. At POH, across application rates, the OA treatments increased the Olsen-P, SOM, Total-C, and TOC by over 37, 23, 75 and 81%, respectively, relative to CNF. Across application rates with or without inorganic fertilizer addition, the OA treatments did not significantly affect the CEC as compared with CNF. The OAs increased the P, K and Mg indices relative to the CNF which increased with increase in OA application rates. Further, the OA treatments increased the MBC by 72-95% (p <0.05) and reduced microbial stress by over 30% relative to CNF. Without inorganic fertilizer addition, the OA treatments increased the above ground and below ground plant biomass (AGDB and BGDB) by 24-65% and 38-88% respectively, compared with the CNF treatment except for the PAS treatments. The OAs had 100% increases in cob yield as compared with CNF, except for PAS1NF/2NF and AD_SW1NF treatments. Inorganic fertilizer addition had marked effects on plant performance, particularly when combined with the PAS OA. The study concludes that application of OAs has the potential to improve soil health and productivity of a degraded sandy loam soil. Long term effects of these OAs merit further detailed exploration.