Effect of quantity and frequency of irrigation on growth characteristics and soil water balance of tomatoes in greenhouse: case study of Kitui County
The study was conducted in two greenhouses located at Matinyani Secondary School and Kyondoni Village, Kitui County, Kenya. Variation of tomato crop growth characteristics, yield and soil water content were monitored. These growth characteristics included plant height, stem diameter, fruit diameter and fruit weight. Four irrigation water application levels served as treatments. These were 120, 100, 80 and 60 % of crop water requirements computed using Priestley-Taylor model (T1-1.2, T2-1.0, T3-0.8 and T4-0.6). The irrigation frequencies corresponded to daily and alternate (skipping one day) at Matinyani and Kyondoni respectively. Applied irrigation water varied from 548 to 274 mm for daily irrigation and from 255 to 128 mm for alternate irrigation while actual evapotranspiration varied from 537 to 246 mm for daily irrigation and from 227 to 108 mm for alternate irrigation for all treatments. A significant reduction in growth parameters (plant height, plant diameter and stem diameter), yield and soil water content was observed based on reductions in irrigation water applications and frequency. Daily irrigated treatments produced the best growth parameters, the best fruit quality and the highest yield. In this regard, treatment T1 produced the largest stem diameter, plant height, fruit weight, fruit diameter and the highest yield as 16.74 mm, 2.31 m, 129 g, 62 mm and 4.44 kg m-2 respectively while treatment T4 produced the highest IWUE and WUE as 11.90 and 13.26 kg m-3 respectively. The average water requirement per plant per day for Anna F1 tomato variety was 1.35 litres at Matinyani and 1.28 litres at Kyondoni. This variation was attributed to the changes in the microclimate within the greenhouses which could have been due to the changes in the global climate. Open field cultivation is low yielding and risk prone in Kitui County hence the use of greenhouses will protect crops from harsh weather alongside decreasing crop water requirements because the plastic cover creates a barrier to moisture loss. The results of this study revealed that the growth parameters and yield in treatment T3 were not different from those in treatments T1 and T2. Therefore, in situations where water resources are scarce, treatment T3 (80 % ETc) on daily irrigation frequency is considered the appropriate quantity for tomato crop grown in a greenhouse and therefore recommended. An understanding of tomato growth characteristics and soil water balance will provide alternative means by which proper and efficient water management practices in greenhouses can be achieved. Further, a study of this nature can help in understanding the total optimal amount of water required to raise a crop in a greenhouse and this would help in estimating the size of storage facilities needed to store the amount of water harvested from the greenhouse.
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