Nematode control and soil fertility improvement in banana using sunn hemp in Uganda

Abstract

Root-infecting nematodes and declining soil fertility are among the major problems limiting banana production in Uganda. Root-infecting nematodes can cause 100% yield loss. Information on synergistic management of nematodes and soil fertility in smallholder farming communities is limited. This study investigated the potential of sunn hemp (Crotalaria juncea) for managing banana root nematodes and replenishing soil fertility. Field, laboratory and greeen house experiments were conducted in Central Uganda on banana cultivar “Mbwazirume”. Treatments for the field experiments included C. juncea imported, C. juncea intercropped and no C. juncea. Plantlets were inoculated three months after planting with root infecting nematodes Helicotylenchus multicinctus, Radopholus similis, and Meloidogyne spp. The importing of C. juncea was done before nematode inoculation. Roots were sampled for nematode assessment every three months during fiteen months. Crotalaria juncea imported preceeded other treatments in reducing Radopholus similis. The treatments reduced Radopholus similis from 11,000 to 2,500 but had no significant effect on Helicotylenchus multicinctus. In the last 12 – 15 months the R. similis numbers resurged from 2,500 to 5,000. In the field, banana plant growth parameters were measured monthly for eighteen months. The results showed the tallest and biggest banana plants with the longest leaves where C. juncea was imported. The banana plants were 30 cm taller than those in the control. Pre- experiment soil analysis (0 – 15) results were obtained and compared with those after treatment application at eighteen months. Soil samples were taken thrice for routine analysis every after six months At the end of the experiment most of the soil nutrients mainly organic matter and nitrogen significantly (p<0.01) increased and were highest where C. juncea was imporeted. P was sub-optimal at the beginning and end of the experiment. In spite of this, it increased significantly (p<0.02) and was also highest in the C. juncea imported treatment. The laboratory experiments were conducted to assess which part of C. juncea is most effective in controlling nematodes. Different parts of C. juncea were harvested from 8 weeks old plants and crude extracts obtained from them. Radopholus similis nematodes were introduced in the extract and left to stand in the laboratory for 24 hours at about 250 C. Dead and live nematodes were counted after 24 hours and the study was repeated five times. Crotalaria juncea leaf extract killed 75% of Radopholus similis and was followed by the root extract. The pods and flowers were the least effective and killed 25% of Radopholus similis. Every part of Crotalaria juncea can be used to reduce nematode numbers. In the green house eperiment, the plant height and girth were significantly tall but there was no difference in the leaf length and leaf width within the treatments. The plants in the Crotalaria. juncea incorporated treatment were 5.5 cm taller and the girth was 2.7 cm bigger than the control. Radopholus similis numbers reduced by 68%. C. juncea can be incorporated before banana plant establishment for improved performance and nematode control.