Breakdown of dry aggregates by water drops after applications of poultry manure and spent mushroom wastes

Evaluation of soil properties that enable aggregates to resist breakdown from impacting water drops is useful in modeling soil erosion process and tillage of some tropical soils. The effect of applications of poultry manure and spent mushroom wastes on soil properties related to resistance of aggregates of a degraded ultisol to water drops detachment energy (D) in southern Nigeria was studied. The area was under continuous field trials for maize crop. The treatments were: control (PM0SM0), 5 and 10 t ha⁻¹ poultry manure (PM5 and PM10, respectively), 5 and 10 t ha⁻¹ spent mushroom wastes (SM5 and SM10, respectively), and 5 t ha⁻¹ poultry manure plus 5 t ha⁻¹ spent mushroom wastes (PM5 + SM5) applied in seven consecutive years. Experimental design was a randomized complete block design (RCBD) in five replications. Soil samples were analyzed for texture, organic matter, aggregate stability, water retention, bulk density, clay mineralogy and water drop test. Results revealed that seven-year applications of PM5, SM5, SM10, and PM5 + SM5 treatments had significant positive effects on soil structural and hydraulic properties than PM10. However, in comparison to PM0SM0, applications of 10 t ha⁻¹ PM had significant positive effects on these properties. Saturated hydraulic conductivity was 46.6, 35.4, 32.6 and 25.5 cm h⁻¹ in PM5 + SM5, SM10, SM5 and PM10 soils, respectively; compared to 9.6 cm h⁻¹ in PM0SM0. A low aggregate ratio (AR) obtained for PM10 compared to higher values for SM10 and PM5 + SM5 suggest that PM10 in this case had a disaggregating effect on the soil aggregates. Sand content accounted for 81.2% of negative effect on water drop detachment energy (D), while clay content accounted for 86.8% of the positive correlation with D. Only water-stable aggregates (WSA) 0.5–0.25 mm had a significant positive correlation with D (r = 0.661, p < 0.05). Clay dispersion index (CDI) had a highly negative correlation with D (r = − 0.896, p < 0.01). Volumetric water content at FC (− 10 kPa) and PWP (− 1500 kPa) correlated positively with D (r = 0.618, P < 0.05 and r = 0.614, p < 0.05). There was a non-significant positive correlation of Muscovite and Berlinite with D. Significant positive correlations of calcite with D (r = 0.694, p < 0.05), and between mica and D (r = 0.731, p < 0.05), revealed their strong linkage with macro-aggregate stability. It was found that high rates of poultry manure alone could increased erodibility and decreased water retention at FC and PWP, while a combination of poultry manure and spent mushroom wastes could reduce erodibility. These properties could be used to make a quick inference on the resistance of soil aggregates to water drop impact.