Effects of drought, nitrogen, spacing and defoliation on vegetative growth and development, yield and quality of kale (brassica oleracea var. acephala
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There is hardly any study reported in literature on the cultural practices for vegetable kale production. Greenhouse and field experiments were conducted to study the effects of drought, three water regimes (irrigating when available soil moisture had been depleted to 75, 50 or 25 percent), two spacings (21,489 or 42,978 plants/ha), two rates (0 or 135 kg/ha) of N side-dressing, defoliation and supplementary irrigation on growth, development, yield and quality of vegetable ~ale plants. During wilting of kale plants, young leaves retained more water than the old leaves. The old leaves became senescent and were shed. Irrigating when the plants had depleted available soil moisture to 75 percent did not significantly differ from irrigating when soil moisture had been depleted to 50 percent. However, allowing the plants to deplete the available soil moisture to 25 percent significantly retarded their growth. Drought at an early growth stage of the plants did not significantly affect their growth and development. However, drought at any stage of growth of the plants reduced yield. Wide spacing increased fresh and dry weights, number of leaves and branching per plant, whereas close spacing increased total above ground, leaf and marketable yields. Nitrogen side-dressing increased fresh and dry weights per plant of widely spaced plants only. Nitrogen side-dressing did not have significant effects on quality of kale leaves. However, irrigating side-dressed plants, and wide spacing, increased nitrate-N content in the leaves. Close spacing increased dietary fiber ~nd thiocyanate ion contents in the leaves. Defoliation increased final cumulative number of leaves and harvest index but decreased plant height, branching and fresh and dry weights per plant, and unmarketable leaf yield per hectare. Defoliating widely spaced plants decreased the final total cumulative yield per hectare. Defoliation x nitrogen and spacirtgx supplementary irrigation interaction was significant for leaf production on the axillary branches, and total nitrogen content of the leaves. Main effects of nitrogen, spacing, supplementary irrigation and defoliation on the contents of macro- and microelements, in the plants, were not significc~t.