Structural Stability and Hydraulic Properties of Two Coarse-Textured Soils As Affected By Organic Amendments and Duration of Soil-Amendment Mixture

Abstract

The application of organic amendments to soil can enhance its structural and hydraulic properties. In this study, the structural stability and hydraulic properties of two coarse-textured soils as affected by organic amendments and duration of soil-amendment mixture were assessed in a glasshouse. The soils were sampled from University of Nigeria, teaching and research farm at Nsukka in Enugu state and Isinyi Nando in Anambra state. The soils have the same textural class (Sandy loam), and differed in organic matter status (28 and 16.2 g/kg respectively). The experiment was laid out in a completely randomized design (CRD) with 20 (4x5) treatments replicated three times, giving 60 potted soils for each soil. Soybean (creeping type) was used as a test crop. Soils were air-dried, crushed and treated with organic amendments (poultry dropping (PD), pig slurry (PS), cattle dung (CD) and control (CONT) unamend). The soil and amendments were mixed homogenously in a soil-manure ratio of 1500:45 on dry mass basis and watered to field capacity at three-day intervals till the end of glasshouse trial. Amendments of the soils and potting was done in stages over five-time intervals, such that there were potted soils lasting 2, 6, 10, 14, and 22 weeks at soybean planting, corresponding to 8, 12, 16, 20, and 28 weeks after mixing and potting, respectively at soybean harvest done six weeks after soybean planting. At harvest, soybean plants were cut off from the base carefully and dry matter yield assessed. Undisturbed samples were collected at 0-5cm depth along with disturbed samples for the assessment of aggregate stability and other physicochemical properties, which were analyzed using the standard laboratory procedures. Data collected were analyzed using two-way analysis of variance for a factorial study in CRD. Results showed that the application of organic amendments had a highly significant (p < 0.01) increase in structural stability indices, saturated hydraulic conductivity (Ks) and lower bulk density than control. The maximum values of mean-weight diameter (1.69 and 1.65 mm), aggregate stability (41.5 and 51.10 %), and waterstable aggregate (18.25 and 16.62 %) were observed in the pots amended with CD for both soil and the degree of improvement follows this trend CD> PD> PS> Control. Application of organic amendment also reduced the bulk density of the soils relative to the control. Furthermore, application of organic amendments had a significantly (p < 0.05) higher values in Organic matter (OM), available P, pH and CEC when compared to the control, with CD having the highest value of % OM ( 4.06 and 2.21 %) and PD having the highest value of pH ( 7.2 and 7.0) and available P ( 92.3 and 114.7 %) respectively for both soils. The study indicated that a highly significant (p < 0.01) positive correlation was found between OM and, aggregate stability, water-stable aggregate, mean-weight diameter, percolation stability, bulk density, and Ks for both soils. Organic matter also showed a significant positive and negative relationship with dispersion ratio and aggregated silt + clay (0.626** and -0669** respectively) for Isinyi-Nando soil. The plant dry matter yield assessed increased with application of organic amendments relative to the unamend pots for both soil. The plant dry matter yield correlated positively with WSA and available P for UNNNsukka soil, while no correlation was found between plant dry matter yield with the parameters of IsinyiNando soil. The results from this study showed that an adequate application of organic amendments stabilized soil structure and enhanced soil productivity especially the soils in southeastern Nigeria, which are often low in organic matter. However, effects of different organic amendments on structural stability and hydraulic properties of soil could be soil dependent and the magnitude of improvement or enhancement is a function of soil type and manure type.