Growth and Water-Yield Functions of Dry-Season Fadama-Grown Pepper (Capsicum annuum L.) Under Differential Irrigation in a Rainforest Zone of Nigeria

Field experiments were conducted to assess the effects of differential irrigation on the growth, stress development and water- yield functions of dry season fadama-grown pepper in a humid rainforest zone of Nigeria. The aims were to characterize water productivity of pepper (crop yield production functions) and develop the drought response factor Ky in relation to irrigation (Ir) and total crop water-use (ETc). Four irrigation treatments were studied based on the restoration of depleted soil moisture (the levels of cumulative pan evaporation: Epan). These were 100%, 80%, 60%, and 40% of EPan which indicate relative water deficit of 0, 0.2, 0.4 and 0.6 respectively in order to attain maximum and minimum plant water stress conditions. Irrigation was fixed at 5 days-interval at EPan coefficient (Kcp) of 0.70 and accumulated pan evaporation. The amount at each irrigation and seasonal sum of irrigation were 4.82 l/day; 127500 mm and 1.93 l/day; 20400 mm for the respective well irrigated control (DI1) and the more stressfull (DI4) treatment. Fruit yields of pepper plants declined with increasing soil moisture deficits. Highest fruit yields were obtained under the well watered control (DI1; 11.2 t/ha) and lowest under the highest deficit irrigation (DI4; 7.1 t.ha−1). Maximum water use efficiencies (IWUE and WUE) were observed in D11 (0.88 and 1.52 kg. m−3) and minimum in D14 treatments (2.73 and 1.33 kg. m−3). The values of irrigation and crop water use (evapotranspiration) efficiencies were (IWUE; 0.80, 1.12, 1.81 and 2.73; WUE (ETE;); 1.34, 1.54, 1.56 and 1.61 mm of water per ton dry matter respectively. The moisture stress sensitivity indices (drought response factor, ky) were computed from a: the relative yield (Ya/Ym) and the relative evapotranspiration (ETa/ETm) and b: relative yield (Ya/Ym) and soil moisture deficit (SAWa/SAWm) relationships of the water production models. The mean ky were 0.92 and 2.25 for the respective a and b models and 1.79 and 2.30 for the respective D/2 and D/4 treatments. The results indicated that the adopted models (a and b) are valid to be used to predict pepper yield under different irrigation applications.