LAND PREPARATION, MULCH APPLICATION AND IRRIGATION EFFECTS ON SELECTED SOIL PROPERTIES AND OKRA [Abelmoschus esculentus (L.) Moench] YIELD ON AN ULTISOL

Abstract

Decline in soil physical and chemical properties, and scarcity of water are major constraints to dry season okra cultivation. Appropriate land preparation and mulch application under irrigation water management could enhance soil properties and moisture availability for optimum crop yield. However, there is a dearth of information on the effects of land preparation and mulch application on soil properties and okra yield under dry season irrigation conditions. This study was therefore conducted to determine the combined effects of land preparation, mulch application and irrigation rates on soil properties and okra yield on an ultisol. In a screenhouse experiment, two okra varieties (UI4-30 and NH47-4) were grown in drainage lysimeters containing 14 kg soil. Irrigation water was applied based on three reference evapotranspiration (ETo) rates: ETo from the Nigerian Meteorological Agency (ETo-N), ETo from the International Institute of Tropical Agriculture (ETo-I), and the mean of ETo-N and ETo-I (ETo-M). The experiment was laid in a completely randomised design with three replicates. Okra evapotranspiration-ETc (mm day-1) was determined using standard procedure across 10 weeks after sowing, while Okra Pod Yield-OPY (g plant-1) was estimated over the harvesting period. On the field, effects of three each of land preparation types (Raised Bed-RB, Ridge and Flat) mulch types (Gliricidia sepium Mulch-GsM, Pennisetum purpureum Mulch-PpM and Zero Mulch-ZM) and irrigation rates (100% ETc, 75% ETc and CROPWAT rate-CRW) were investigated. Treatments were laid as a 3 × 3 × 3 factorial in a randomised complete block design with three replicates. Okra variety UI4-30 was planted at a spacing of 30 × 45 cm. Water Stable Aggregates-WSA (%) and Soil Organic Carbon-SOC (g kg-1) were determined using standard procedures, while Number of Pods per Plant (NPP) and OPY were estimated over the harvesting period. Data were analysed using descriptive statistics, t-test and ANOVA at α0.05. The ETc for UI4-30 (2.46±0.21) and NH47-4 (2.39±0.18) were not significantly different and ranged from 1.00±0.10 (ETo-I) to 3.97±0.78 (ETo-N) and 1.04±0.08 (ETo-M) to 3.62±0.94 (ETo-N), respectively. Across varieties, okra ETc differed significantly and were in the order: 2.89±0.24 (ETo-N) > 2.33±0.19 (ETo-M) > 2.04±0.16 (ETo-I). Across ETo rates, OPY of UI4-30 (10.14±1.17) was significantly higher than that of NH47-4 (8.97±1.28). Plants under ETo-N had the highest OPY (10.67±0.33), followed by ETo-M (9.63±0.80) and ETo-I (8.37±0.84). On the field, WSA differed significantly among the treatments and was highest under RB+GsM+CRW (62.29±1.26) and lowest under RB+ZM+CRW (51.22±0.20). However, WSA under RB+GsM+CRW (62.29±1.26) and RB+GsM+75% ETc (55.60±0.31) were similar. There was no significant difference in SOC among the treatments. The SOC ranged from 13.1±0.19 (Flat+ZM+75% ETc) to 24.45±1.11 (Ridge+GsM+CRW). The NPP and OPY were significantly different among the treatments. The NPP ranged from 3.1±0.10 (Ridge+ZM+CRW) to 11.6±2.60 (RB+GsM+75% ETc), while OPY ranged from 8.32±1.17 (Ridge+ZM+CRW) to 57.17±12.04 (RB+GsM+75% ETc). Raised beds, mulch application using Gliricidia sepium and irrigation rate at 75% okra evapotranspiration rate enhanced water stable aggregates, soil organic carbon and okra pod yield on an ultisol.