Investigations of agronomic practices to improve the establishment and yields of Amaranthus Hybridus and Cleome Gynandra

Abstract

Many people are becoming increasingly aware of the importance of indigenous African leafy vegetables in meeting their household food security, and are therefore producing them in their home gardens and farms. There is however not enough information regarding agronomic practices for their optimum productivity. In an effort to investigate viable techniques of producing indigenous leafy vegetables among local communities, this study was carried out to test agronomic practices that can be used to improve the establishment, growth, productivity and quality of two dominant indigenous African leafy vegetables (IALVS) namely, Amaranth us hybridus and Cleome gynandra. The effects of seed sowing depth on emergence and early seedling development of Amaranthus hybridus and Cleome gynandra, was investigated in a glasshouse study. Eight sowing depths (1.5, 3.5, 7, 10, 15, 20, 25 and 30 mm) were imposed on seeds of two African indigenous (Amaranthus hybridus and Cleome gynandra) and exotic (Spinacia oleracea and Brassica napus) leafy vegetable species using a split plot design with four replicates. Exotic vegetables had significantly higher (p<0.05) seedling emergence (95%) than the indigenous ones (60%). Among the indigenous species, Cleome gynandra had a higher emergence (70%) than Amaranthus hybridus (61 %). However, there were no significant differences on emergence amongst the exotic vegetables. Exotic vegetables also had significantly higher (p<0.05) mean plant height (8.6 cm) than indigenous vegetables (1.01 cm). In all the vegetable species, both emergence and plant height decreased with deeper sowing due to higher soil strength. The biomass yields of the seedlings were reduced with deeper sowing although the differences were not significant. There were however significant differences (p<0.05) among the biomass yields of the vegetable species at different sowing depths. Generally, significantly higher biomass yields (6.4 g/plant) were obtained in exotic species compared with indigenous ones (0.2 g/plant). The results suggest that seeds of indigenous African leafy vegetables were more sensitive than the exotic ones to deeper (>10mm) sowing and their emergence was more adversely affected by soil strength at this depth. Both deep (15-20mm) and shallow (<10mm) sowing depths reduced the emergence of seedlings of both species of IALVS studied. It was thus concluded that an optimum stand of IALVS can be obtained if the seeds are sown at optimum depth of 10 mm. The effects of applying kraal manure (cattle, goat and control) and leaf cutting management (cutting edible tender tips only, cutting all leaves and cut all the leaves only at the end) on leaf biomass yield of indigenous African leafy vegetables Cleome gynandra and A. hybridus were studied. The plants were grown in large PVC pots laid in a randomized complete block design and leaves were cut five times before the final harvest. Applications of kraal manure improved leaf biomass yield of both vegetables and the yield was increased with successive cutting where kraal manure was applied. Plants that were grown in soil amended with goat manure produced significantly higher total fresh leaf biomass yield (470.86 g pot⁻¹) than those under cattle manure (328.42 g pot⁻¹) in C. gynandra. A similar observation was made in A. hybridus plants. The results showed that fresh leaf biomass of C. gynandra and A. hybridus were increased when kraal manure was added. The yield was higher in goat manure when all the leaves were cut than in cattle manure for both vegetables. It was observed that in all the cutting techniques, plants that were not amended with kraal manure produced the lowest crude protein content while the highest CP content was obtained from the plants that were amended with kraal manure across all the cutting techniques. The biomass yields of both vegetable species in the treatments with manure increased progressively with each harvesting while those in the control declined. Plants where all the leaves were cut produced significantly higher total yields (371 g pot⁻¹) compared with cutting only edible tender leaves (342.83 g pot⁻¹) and cutting all the leaves at the end (165.35 g pot⁻¹). A combination of goat manure and cutting all leaves gave the highest fresh leaf biomass yield (571.99 g pot⁻¹) while the corresponding yield for cattle manure was (439.69 g pot⁻¹). The results revealed variations among the two manure types with goat manure being superior to cattle manure. It was concluded that the yields of Cleome gynandra and Amaranthus hybridus could be increased by adopting an appropriate manure and leaf cutting technique. In order to determine the influence of phosphorus fertilizer and leaf cutting techniques on biomass yield and quality of leaves of amaranthus (Amaranthus hybridus) and cleome (Cleome gynandra), an experiment was conducted in pots where single super phosphate (SSP) fertilizer was applied at rates equivalent to 0, 20, 40 and 60 kg ha⁻¹. Phosphorus application significantly (P<0.05) increased leaf biomass yields compared with the control. The biomass yields of both species increased with increasing P level with plants that received 60 kg P ha⁻¹ producing significantly (P<0.05) higher total fresh leaf yield (266.7 g pot⁻¹) than in 20 and 40 kg ha-1. Application of P fertilizer also contributed to increased fresh stem and root biomass of both C. gynandra and A. hybridus. In both vegetable species, highest fresh leaf yield was obtained from the plants whose leaves were all cut leaving mature leaves and stems while lowest yields were obtained when plants were cut once at final cut. There was a high moisture content in plants whose leaves were cut throughout while the lowest moisture content was obtained from plants that were cut once at the end. The biomass yields increased with increasing P rates across all cutting techniques in both vegetable species. A combination of fertilizer at 60 kg P ha-l and cutting all leaves throughout produced highest fresh leaf yield. The results indicated that crude protein was decreased when leaves were cut once at end of the study across all the phosphorus rates. Highest crude protein content was obtained when all leaves were cut at all P rates in both vegetable species. It was concluded that leaf cuttings with high rates of P fertilizer can contribute to improved biomass yield production of the two indigenous African leafy vegetables. In both C. gynandra and A. hybridus, the crude protein in leaves was enhanced by application of kraal manure with goat manure producing higher crude protein than cattle (14.2% vs 13.4%, respectively) and (12.2% vs 11.44%, respectively). Application of phosphorus significantly (P<0.05) increased the crude protein content of vegetable leaves. Frequent cut of leaves enhanced crude protein production while cutting leaves once at final cut produced lowest crude protein. It was concluded that the crude protein content of IALVS can be improved by P fertilizer and frequent cut of leaves of IALVS. Not withstanding the limitation of practical application of pot growth experiments, the significance of this study is that, the findings can help to promote the production of IALVS by providing the necessary agronomic information for their cultivation. The results of this study indicate that planting depth and fertility management are important for improving productivity and should however be confirmed under different field conditions and for longer experimental duration to provide recommendations for farmers.