Title : Effect of irrigation level and different soil amendments on vegetable yield and soil water storage, in the semi-arid central
Abstract:
The two field experiments assessed the effects of irrigation difference as main plots (4 days and 2 days in experiment 1, and 5 days and 4 days in experiment 2, for full and reduced irrigation, respectively) and six soil amendments; biochar, compost, zeolite, NPK, be-grow and hoof and horn + bone meal (HHB) as subplots, on cabbage production. Six plants from the two middle rows of soil amendment plots were randomly selected for data collection; head girth and head weight. In addition, the marketable heads for each amendment were extrapolated to per hectare and multiplied with average head weight to determine cabbage yield (t ha-1). Water use efficiency was calculated as the fresh trimmed cabbage yield (t ha-1) produced from the amount of water applied. In experiment 1, full irrigation produced significantly higher yield (21.13 t ha-1), average marketable head weight (0.958 kg) and bigger head girth (42.05 cm), compared to 14.71 t ha-1,0.782 kg and 39.79 cm, respectively under the reduced irrigation. Zeolite, biochar and be-grow produced significantly highest and similar yield of 22.66 t ha-1, 22.59 t ha-1 and 22.27 t ha-1 respectively, compared to 10.30 t ha-1 under the control. In addition, biochar followed by be- grow, zeolite and NPK gave the highest and statistically similar marketable heads of 24884 heads ha-1, 23938 heads ha-1, 22801 heads ha-1 and 22454 heads ha-1, compared to the control (14873 heads ha-1). Furthermore, biochar, be- grow and zeolite had the highest and similar water use efficiency of 76.02 kg ha-1 mm-1, 74.36 kg ha-1 mm-1 (be-grow and zeolite) compared to the control (35.74 kg ha-1 mm-1). Moreover, biochar recorded the biggest head girths of 42.67 cm, with the lowest recorded under the HHB (36.50 cm) and control (37.00 cm). In experiment 2, the irrigation difference had no significant impact on cabbage performance. In addition, HHB, produced the highest yield, head weight, head girth and water use efficiency of 49.49 t ha-1, 1.914 kg, 62. 57 cm and 143.3 kg ha-1 mm-1, compared to the control; 17.19 t ha-1, 1.109 kg, 51.07 cm and 50.5 kg ha-1 mm-1, respectively. The highest marketable heads were recorded under the be- grow (27489 heads ha-1) and the lowest under the control (14873 heads ha-1). Moreover, be-grow under full irrigation, produced the highest marketable yield (28935 heads ha-1) followed by HHB under reduced irrigation (28703 head ha-1), NPK under full irrigation (28009 heads ha-1) and biochar under full irrigation (27546 heads ha-1) both of which were statistically similar; the fully irrigated control produced the least marketable heads (9028 heads ha-1). Compared to other soil amendments, zeolite retained the highest plant available water (PAW) when fully irrigated but also the least PAW under the reduced irrigation; HHB had the highest PAW under the reduced irrigation compared to other amendments. A combination of biochar and HHB under moderate irrigation could thus be implemented for improved vegetable production in central Namibia.
