Aggregate stability responses of three derived-savannah soils to poultry-droppings manure at different pulverisation-to-sampling time intervals
Authors:   Department of Soil Science, Faculty of Agriculture, University of Nigeria, Nsukka 410001, Enugu State, Nigeria, Ewele Obalum Sunday ,   Department of Soil & Environmental Management, Faculty of Agriculture, Prince Abubakar Audu University, Anyigba, PMB 1008 Anyigba, Kogi State, Nigeria, Ikpi Ofem Kokei ,   Department of Soil Science, Faculty of Agriculture, University of Calabar, PMB 1115, Calabar, Cross River State, Nigeria, Chinenye Nwamba Doris ,   Department of Soil Science, Faculty of Agriculture, University of Nigeria, Nsukka 410001, Enugu State, Nigeria, Omaye Joseph Paul ,   Department of Soil & Environmental Management, Faculty of Agriculture, Prince Abubakar Audu University, Anyigba, PMB 1008 Anyigba, Kogi State, Nigeria, Gloria Edeh Ifeoma ,   Department of Soil Science, Faculty of Agriculture, University of Nigeria, Nsukka 410001, Enugu State, Nigeria, Cyprian Amalu Uche ,   Department of Soil Science, Faculty of Agriculture, University of Calabar, PMB 1115, Calabar, Cross River State, Nigeria, Arizechukwu Igwe Charles ,   Department of Soil Science, Faculty of Agriculture, University of Nigeria, Nsukka 410001, Enugu State, Nigeria
Published: September 2024

Organic inputs to tillage-pulverised soils could, by facilitating soil structure reformation with time, enhance environmental quality. This study examined the aggregate stability responses of three texture-contrasting soils from the derived savannah of southeastern Nigeria to poultry-droppings (PD) manure over time. The soils from Nsukka, Ukehe and Adani with clay contents of 53, 100 and 260 g/kg had antecent organic matter concentrations of 18.77, 29.73 and 16.23 g/kg, respectively, with sandy Nsukka/Ukehe being more stable than loamy Adani. Pulverised soils were amended with PD at rates equivalent to 0, 10, 20, 40 and 70 t/ha, watered and open-incubated under glasshouse conditions. They were augmented to field capacity at three-day intervals and sub-sampled at 2, 4, 8, 12, and 20 weeks after incubation (WAI). Treatment effects were highly soil-dependent. For all three soils, water-stable aggregates, mean-weight diameter (MWD) of aggregates and sand-corrected water-stable aggregates were highest with 70 t/ha at 20 WAI which showed similar MWD of aggregates as 0 t/ha at 20 WAI. Also, 70 and 20 t/ha each at 20 WAI consistently had similar effects (Adani only). Treatment effects on soil bulk density were irregular, with the highest values mostly at 20 WAI across rates. Thus, soil bulk density related inversely with aggregate stability only during 2-12 WAI, owing to their concurrent increases with soil pH beyond 12 WAI. These soil structure indices were not influenced by PD-induced fluctuations in electrical condutivity which always peaked 4 WAI. Heavy and modest PD addition, respectively, to tillage-pulverised sandy and loamy tropical soils promote their re-aggregation after 20 weeks; however, such soils even without manuring could re-structure into aggregates of sizes as though PD-amended over this long interval. Rather than PD-induced salinisation, it is soil pH that influences macro-aggregation up till the 20th week, when soil pH should be ≤ 6.65 to avoid soil densification above 1.71 Mg/m3.