Alternative sources of plant nutrients have now become highly imperative especially for vegetable crop production in Nigeria. Due to the escalating costs, environmental and health problems associated with excessive use of inorganic fertilizers on continuously cropped fields, there is a need for more research on the use of organic manures and residues. A field experiment was conducted in the late growing season from September to December, 2012 in Calabar, a humid forest agroecology in south eastern Nigeria to evaluate the effects of two types of goat manure (GM) application (single and double split doses), five rates of GM (0, 5, 10, 15 and 20 t ha -1 ) and 400kg ha -1 NPK fertilizer (120:60:60 kg ha -1 ) rate on soil chemical properties and agronomic performance of sweet maize (Zea mays L. saccharata Strut). Factorial combinations of the treatments were fitted into a randomized complete block design with three replications. The application of GM significantly (P ≤ 0.05) increased soil pH, organic matter (OM) content, total N, available P, exchangeable K, Ca, Mg and the cation exchange capacity (CEC) status of the soil. Soil exchangeable acidity (EA) was reduced from 1.76 to 0.64 cmol kg -1 at 20 t ha -1 GM rate. The 20 t ha -1 also recorded the highest values for soil pH, OM, P, Ca, Mg and CEC, while the values for residual N and K peaked at the NPK fertilizer treatment. The double split application of GM recorded higher values for growth and yield attributes, and increased soil properties than the single application. Growth and yield parameters such as plant height, number of leaves, leaf area index (LAI), total dry matter (TDM), number and weight of grains/ear and total grain yield were significantly (P ≤ 0.05) increased by GM and NPK fertilizer treatments. The values obtained for all growth and yield parameters except LAI at the 20 t ha -1 GM rate were not significantly different from those at the NPK fertilizer treatments. The application of 5, 10, 15 and 20 t ha -1 GM, and NPK fertilizer significantly increased TDM by 11.9, 74.3, 91.9, 106.2 and 104.6%; weight of grains/ear by 16.5, 54.6, 61.4, 100.6 and 94.4% and total grain yield by 46.9, 111.7, 121.0, 127.2 and 140.1% respectively, compared with the control treatment. The interactions between number of applications and rates showed that split applying GM at 20 t ha -1 maximized TDM, weights of whole and dehusked green ears and total grain yield compared to other GM rates, hence it is recommended.

A two-year field study was conducted during the growing seasons of 2007 and 2008 in Calabar, south eastern Nigeria to evaluate the response of two improved sweet potato varieties (TIS 8164 and Ex-Igbariam) to five rates (0, 40, 80, 120 and 160 kg K/ha)of potassium fertilizer. Factorial combinations of the treatments were arranged into a randomized complete block design with three replications. Results showed that Ex-Igbariam was more responsive to K application than TIS8164 as indicated by the production of longer vines, higher number of leaves and branches/plant and heavier vine dry weight at all the applied K rates. Averaged across the two years, revealed that Ex-Igbariam out-yielded TIS8164 by 12.5, 12.7 and 13.3% for number of tubers/plant, weight of tubers/plant and tuber yield/ha, respectively. Application of K at the highest rate (160 kg/ha) significantly (P<0.05) increased vine length, number of leaves and branches/plant, whereas dry weight of vine, diameter of tubers/plant and weight of tubers/plant were statistically similar at 120 and 160 kg K/ha rates. Number of tubers/plant and tuber yield/ha peaked at 120 kg K/ha and 160 kg K/ha, respectively. Aggregate tuber yield/ha obtained at 120 and 160 kg K/ha rates were more than 7 and 8 times, respectively higher than the control treatments. Potassium fertilizer application at 120 to 160 kg/ha appeared appropriate for optimum yield for Ex-Igbariam in the study area and is therefore recommended.

A two-year field experiment was carried out on the acidic coastal plain sands of South Eastern Nigeria during the year 2009 and 2010 planting seasons to study the effect of lime levels (L = 0, 500 and 1000 kg ha Results also showed that lime at 500 kg ha -1 gave the highest popcorn yields in 2010, a yield increase of 18.03 % above control, whereas there was no yield response to lime in 2009. Based on the results obtained, it can be concluded that popcorn sown at 80 kg N ha -1 and 500 kg ha -1 rates of lime significantly increased the crop productivity compared to those sown at other N and lime rates. The study demonstrated the effect of lime amendment in reducing rates of inorganic N applied to popcorn especially with resource poor farmers who form the bulk of maize producers in Nigeria.

The response of cocoyam (Colocasia esuclenta (L.) Schott) to various rates of poultry manure (PM) and potassium(K) fertilizer was studied under field conditions in 2006 and 2007 growing seasons at Uyo, a humid forest agroecology of south eastern Nigeria. Treatment combinations comprising of four rates each of PM (0, 5, 10 and 15t/ha) and K (0, 40, 80 and 120 kg K/ha) were factorized and fitted into a randomized complete block design with three replicates. Application of PM and K at the highest rates produced significantly taller plants with higher leaf area index, shoot dry matter, corms and cormels number, compared with other treatments in both years. Weight of corms and cormels and total yield (t/ha) were however, optimized at 10t/ha and 80 kg K/ha rate. Averaged over the two years, increases in PM and K rates from zero to 15t/ha and 120 kg K/ha, increased the shoot dry matter by 51% and 29%, and the number of corms and cormels by 40% and 34%, respectively. Weight of corms and cormels and total yield obtained in the two years at 10t/ha and 15t/ha PM, and 80 kg K/ha and 120 kg K/ha were statistically similar except in 2007 where the corms and cormels weight peaked at 15t/ha PM rate. Poultry manure at 15t/ha in combination with either 80 kg K/ha or 120 kg K/ha out-yielded other treatments in terms of corms and cormels weight and total yield in the two years of trial.

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