Assessing the productivity of grain cowpea under variable conditions using low-input agricultural production practices

MSc (Crop Science), North-West University, Mafikeng Campus, 2019

The adoption of low-input agricultural practices can play a vital role towards ensuring food security. Cowpea is an indigenous crop that is highly adaptive and has numerous benefits. However, its production in South Africa is still very low with smallholder farmers being the largest producers of the crop in the country. The study focused on efforts to maximise the production of cowpea, particularly for smallholder farmers using low-input agricultural practices, which could ensure sustainable production and enhance food security. The aim of this study was to investigate the impact of low-input agricultural practices on the productivity of grain cowpea grown under tunnel house and dryland conditions. Phospho-compost prepared at the Molelwane experimental farm of North-West University using animal manure (cattle, sheep and poultry) and sawdust through co-composting with ground phosphate rock in heap was used for tunnel house and field trials. A repeated 2:x2x6 factorial trial was carried out under tunnel house conditions with one field trial conducted under dryland conditions (these were all done at Molelwane): The tunnel house trials treatment factors consisted of six phosphorus (P) fertilizer rates, two soil types and moisture regimes, replicated three times to obtain 72 pots for both trials. The P fertilizer treatments comprised of variable phospho-compost rates (0, 10, 20, 40 and 80 t/ha) with 30 kg P/ha rate applied as single super phosphate (SSP 10.5%) included as a standard positive control. The soils used in tunnel house trial 1 were from a smallholder farmer's field in Ventersdorp (Glenrosa) and the North-West University experimental farm (Hutton) while the soils for the second tunnel house trial comprised Coega and Hutton soil types collected from the North-West University, Mafikeng Campus. The different P fertilizer rates exerted significant (p:S0.05) influence on all cowpea growth parameters, with the exception of leaf length. Variation in soil types used in the tunnel house trials exerted significant (p:S0.05) effect on stem diameter and chlorophyll content. The highest seed yield (12.51 g/pot) and (8.50) number of pods per plant were recorded in the 40 t/ha phospho-compost rate. Cowpea plants grown under the Coega and Glenrosa soil types performed better than those grown under Hutton soil. Application of 30 kg P/ha resulted in the highest mean nodule count (34.3) under tunnel house l while moisture stress exerted a depressive effect on cowpea seed yield, number of pods and fodder weight. Results obtained revealed that moisture-deprived plants flowered and formed pods quicker The field trial was carried out during 2017-2018 summer growing season, the trial also comprised six phosphorus (P) fertilizer rates and two tillage practices (minimum and conventional). The P fertilizer treatments under the field trial also consisted of variable phospho-compost rates (0, 10, 20, 40 and 80 t/ha) with 30 kg P/ha rate applied as single super phosphate (SSP 10.5%) included as a positive control. Rainfall was used as the main source of irrigation with supplementary irrigation used only when there was a need. Application of 40 and 80 t/ha phospho-compost rates significantly increased the residual Bray P content, organic carbon and total N soil content after harvest. Seed germination and plant emergence was quicker under minimum tillage. Tillage and different fertilizer rates significantly influence all the measured cowpea growth parameters and yield attributes. The highest grain yield (488.06 kg/ha) and nodule count (15 .36) under field conditions were produced at 40 t/ha phospho-compost rate while minimum tillage gave higher grain yield (611.66 kg/ha) and nodule count (14.39) than conventional tillage. Application of phospho-compost resulted in significant increase soil available P and cowpea plant tissue P content. The heavy metal content of cowpea grains from the different fertilizer rates and tillage practices did not differ significantly (p>0.05) with measured values generally within the threshold level required for human consumption albeit the high Al and Fe concentrations in soil suggesting phyto-toxicity, which may have resulted in low grain yield obtained.

Masters