Comparative evaluation of modified neem leaf, neem leaf and woodash extracts on soil fertility improvement, growth and yields of maize (<i>Zea mays</i> L.) and watermelon (<i>Citrullus lanatus</i>) (Sole and Intercrop)

Abstract

Two field experiments were carried out at Akure (7 o N, 5 o 10 1 E) in the rainforest zone of Nigeria in 2006 and 2007 to determine the effectiveness of neem leaf, woodash and modified neem leaf extracts as fertilizer sources in improving soil fertility, growth and yield of maize ( Zea mays L) and watermelon ( Citrulus lanatus ) sole and intercrop. There were six treatments namely, poultry manure, neem leaf extract (sole), woodash extract, modified neem leaf (neem leaf + woodash), NPK 15-15-15 and a control (no fertilizer nor extract), replicated three times and arranged in a randomized complete block design (RCB). The extracts (neem leaf, wood ash and modified neem leaf) were applied at 1200 litres per hectare each, NPK 15-15-15 at 300 kg/ha and poultry was applied at 6t/ha. The results showed that there were significant increases (P < 0.05) in the maize growth and yield parameters (leaf area, plant height stem girth) grain yield, cob weight and % shelling percentage) as well as in watermelon (vine length, stem girth, number of branches, fruits weight, population and fruit diameter) under sole and intercrop compared to the control treatment. Generally, the growth and yield parameters values were slightly higher under the sole crop than the intercrop. The modified neem leaf extract increased the plant height and stem girth of maize (sole) by 11.78% and 27.43% respectively compared to that of neem leaf extract and the same trend of increase was experienced in maize (intercrop) where modified neem leaf extract increased plant height and stem girth by 11.5% and 24.48% compared to neem leaf. Poultry manure also increased the maize leaf area (sole and intercrop) compared to the extracts and NPK 15-15-15. For instance, under maize (sole), the poultry manure increased the leaf area by 8.74% compared to NPK 15-15-15. For yield parameters of maize and watermelon (sole and intercrop), modified neem leaf increased most all values of yield parameters compared to neem leaf and woodash extract. For example, modified neem leaf increased the values of sole maize grain yield, cob weight by 65.63% and 57.58% respectively compared to neem leaf extract. The LER value for maize and watermelon (intercrop and sole) was 2.61 while relative yield is 1.575 or 157.5%. For soil fertility improvement after harvesting, modified neem leaf extract and poultry manure had the highest values of soil pH (H 2 O), K, Ca, Mg, Na, O.M, P and N compared to NPK 15-15-15 and neem leaf extract. For instance, modified neem leaf extract increased soil pH (H 2 O), K, Ca, Mg, Na, O.M, P and N by 12.4%, 32.8%, 25%, 23.7%, 19.32%, 17.24% and 20% respectively compared to neem leaf extract under intercrop plot. The high soil K/Ca, K/Mg and P/Mg ratios in the NPK 15-15-15 fertilizer treatment led to an imbalance in the supply of P, K, Ca and Mg nutrients to maize and watermelon crops. The least values for growth, yield and soil parameters were recorded under the control treatment. In these experiments, modified neem leaf extract (woodash + neem leaf extracts) applied at 1200 litres/ha was the most effective in improving soil fertility, growth and yield of maize and watermelon (sole and intercrop) and could substitute for 6 tons per hectare of poultry manure and 300kg/ha of NPK 15-15-15 fertilizer.