Effects of Organic Amendments on Soil Structural Enhancement and Deformation Susceptibility in a Degraded Ultisol in Humid Tropics of Southeastern Nigeria

Abstract

Background: Soil structural instability is a severe limitation of sustainable crop productivity in the humid tropics especially in southeastern Nigeria. Aim: To study effects of organic amendments on soil structural enhancement and deformation susceptibility in a degraded Ultisol in humid tropics of Southeastern Nigeria. Methodology: Soil samples were were collected with the aid of soil auger from a depth of 0-20cm and placed in a perforated bag. Every bag holds 10kg of sampled soil. In a randomized complete block design format, 0.25 kg of the organic amendments namely as, poultry droppings (TI), goat droppings, (T2) cow dung (T3), their combinations (T4) were applied in three replicates to each bag.An unamended soil served as control (T5). The combination were allowed to stay for one month before samples were taken for laboratory analyses. Soil physical, chemical and structural indicators were measured after one month of incubation, following standard laboratory method. Results: Results showed that the soils were predominantly sandy (852–910 g kg⁻¹). Bulk density substantially decreased, total porosity and moisture content increased with organic amendment application compared to unamended control sample. The soil chemical properties namely pH, SOC, available P, exchangeable Ca and ECEC were also significantly elevated. Structural indicators viz: water-stable aggregates (>0.25 mm), mean weight diameter (MWD), and the degree of structural enhancement (DSE) significantly (P ≤ 0.05) increased in responses to organic amendments.  The poultry and cattle manure resulted in the greatest DSE values (97.33% and 94.00%, respectively), while that in the control was only 26.38%. This indicates a very high degree of degradation. The study also reveals that pig slurry gave the lowest Potential Structural Deformation Index (PSDI = 40.40%). According to correlation analysis, aggregate stability was negatively correlated with bulk density and strongly positively correlated with soil organic carbon, clay content, and ECEC. Conclusion: The use of locally available animal manure, especially poultry dropping and cow as seen in the result can greatly improve soil structure quality and mitigate the risks of soil degradation in southeastern Nigeria.