Dry season Irrigation Regime Effects on Water Use, Rootzone Moisture and Yield of Cacao (Theobroma cacao L.) in a Rainforest Zone of Nigeria

The humid tropics is characterized by wet-dry seasonal transitions, irrigation has the potential for building adaptation and resilience to climate stress for enhancing crop performance. A field trial was conducted to investigate the effects of dry season irrigation regimes on water use, root zone moisture dynamics and yield of cacao in a rainforest zone of Nigeria. Irrigation amounts computed as EPan x Pan coefficients were based on cumulative class A Pan evaporation. Irrigation treatments were coded as IrT1 (EPan x 1,0), IrT2 (EPan x 0.7) and IrT3 (EPan x 0.5). Irrigation water was applied 5-days interval and discharged via point source emitters (2.8 l/h discharge rate ) on drip lines laterally installed per row of trees. Mean irrigation requirements were 4.49 mm (9.81:9.6 l/tree/day), 3.14 mm (7.06:6.8 l/tree/day) and 2.44 mm (5.49: 4.8 l/tree/day) while total seasonal water applied were 121.19, 84.83 and 60.59 l/tree for IrT1, IrT2 and IrT3 respectively. Mean soil moisture contents and cacao evapotranspiration (ETc) were 52, 45 and 28 % and 4.54, 3.19 and 2.32 mm/day while evaporation from soil area wetted by emitters (EWz) were 5.65, 2.82 and 0.19 mm/day for respective IrT1, IrT2 and IrT3. The deficit irrigation strategies (IrT2 and 31 IrT3) imposed soil moisture deficit stress on cacao and produced lower pod and bean yields, it however enhanced water use efficiencies (25 and 44 %) and 30 and 50 % water savings. The study established suitable Pan coefficients for scheduling irrigation for cacao yield enhancement and drought (climate stress) amelioration.