Response of okra to varying soils, fertilizer levels and moisture regimes under greenhouse conditions.

Abstract

Okra is an economically important vegetable crop that is widely grown in the tropical and sub-tropical regions. The crop is a valued source of minerals and vitamins that are vital for proper maintenance of human health. Regrettably, there is no record of its commercial production in South Africa leading to frequent scarcity and unavailability in the market. The scarcity problem is further exacerbated by the low yield and soil moisture stress due to poor soil fertility and low rainfall amount, respectively as well as its high level of perishability as a fresh vegetable. A factorial greenhouse experiment was conducted at the University of Mpumalanga farm. Trial consisted of two soil textural types (sandy loamy and clay loamy), two moisture regimes (>80% FC and <30% FC) and six fertilizer combinations using different mix ratios of inorganic NPK fertilizer and poultry manure (PM) as treatment factors. The different ratios consist of 100% NPK, 100% PM, 75:25 NPK:PM, 50:50 NPK:PM and 25:75 NPK:PM with an unamended control included as a check. The treatment factors were combined to obtain 24 treatment combinations including the moisture imposition that were each replicated four times. Data collection was at weekly intervals for growth and phenological attributes during the 21 days of moisture treatment imposition. Yield attributes were measured at fruit harvest while mineral quality attributes of harvested fruits were assessed prior to storage and 21 days after storage under room temperature. Results of the study revealed that the integrated use of 75%PM/25%NPK rate significantly (p<0.05) increased okra plant growth and measured yield parameters in moisture stressed and non-stressed in both sandy loamy and clay loamy soils. The highest cumulative number of flowers, fruits, fresh and dry fruit weights as well as fruit length and diameter were recorded in the 75%PM/25%NPK treatment. The report of this study revealed locational difference in yield and growth parameters. Although okra gave the best performance on both soils used in the trial, results from clay loam soil were better than in the soil from UMP farm. The interactive effect of variation in soil textural types and Fertilizer combinations produced significantly highest mean fresh fruit weight (77.02 g/plant), number of flowers (4.56 per plant) and fruits (3.17 per plant), fruit length (39.94 mm) and fruit diameter (81.74 mm) all recorded in clay loam soil under 75:25 mix ratio of PM and NPK fertilizer. Similarly, a significant soil moisture regime and fertilizer interaction produced the highest mean fresh (75.38 g/plant) and dry fruit (6.88 g/plant) weights, number of flowers (4.50 per plant) and fresh fruits (2.81 per plant), and fruit length (38.44 mm) and diameter (80.71 mm) per plant in the non-stressed treatment containing 75:25 PM and NPK fertilizer mix ratio. Application of 75:25 PM and NPK fertilizer mix ratio under sandy loam soil gave the highest measured quality attributes in the non-stressed treatment. Okra fresh weight and the mineral quality attributes were significantly reduced after 21 days of storage with the higher weight loss recorded in the non-moisture stressed treatment. Soil moisture stress reduced the ability of okra to absorb nutrients, which later affected the mineral quality of the okra fruits. Overall, the integrated use of 75:25 mix ratio of this poultry manure and inorganic NPK fertilizer was more beneficial in increasing growth, fruit yield, and mineral nutrients quality of okra plants. The integrated use of 75:25 PM and NPK represents a plausible soil management strategy for promoting increase and sustainable okra production in low fertility soils and moisture stress condition. Nonetheless, collaboration between farmers and researchers is critical for effective implementation of this important agronomic practice to ensure effectiveness at different agro-ecological zones with variable soil types.