Title : Responses of nightshade (Solanum retroflexum) to planting density and irrigation interval under the IDIS water-saving system for smallholder production systems
Abstract:
The water-saving platform, Integrated Drip Irrigation System (IDIS), and the 3S planter – capable of raising from one to nine plants per drip hole- were developed and funded by a grant from the Water Research Commission as a water-saving platform in smallholder farming systems, where the availability of irrigation water is among the major limiting production factors. Nightshade (Solanum retroflexum) is an indigenous leafy vegetable rich in beta-carotene, vitamin E, folic acid, ascorbic acid, calcium, iron, and protein. However, as an underutilised crop, the plant grows in the wild with limited information on its basic agronomic requirements. Determination of the influence of planting density and irrigation interval under IDIS on harvest foliage yield and nutrient elements. The eight treatments, replicated 6 times, were arranged in a split-plot design (Main plot was irrigation interval as geometric series of 2 days; subplot being planting densities ranging from 1 to 9 plants/hole drip irrigation). Harvesting was done twice (H1 = 6 weeks after transplanting, H2 = 6 weeks after H1) for both summer and winter experiments. During each harvest leaves were oven-dried, and leaf mass determined, but leaves were collected mineral content (Ca, P, K, Mg, Na, Fe, Zn, Mn and Cu) at H1 summer, prepared using the digestion method and quantified through the ICPE-9000. Data were assessed for normality and those that complied subjected to ANOVA using SAS software. Although planting density × irrigation interval interactions were significant for both plant growth and the accumulation of minerals, the partitioning of their sum of squares (SS) showed that the contribution to the total treatment variation was negligent and thus effects of the main factors were assessed exclusively. Irrigation interval and planting density each had significant effects on dry mass yield at both harvests regardless of the season, except that the irrigation interval had no significant effects on mass yield at H2 during summer. Irrigation interval had highly significant effects on Ca, Mg, P, K, Na, Fe, Zn, Mn and Cu in leaf tissues at H1 during summer, whereas planting density had no significant effects for all mineral nutrients except for Ca, P and K. The observed quadratic relations allowed the computation of the optimum values for the main factor using the relation: x = – b1/b2b2. The study's findings provided insights into optimising planting density or irrigation interval to derive the optimal benefits from S. retroflexum when produced using the water-saving IDIS platform.
