SIMPLIFIED MICRO-DIFFUSION METHOD OF DETERMINING AVAILABLE, POTENTIALLY AVAILABLE, AND CRUDE PROTEIN BY DIRECT NaOH EXTRACTION IN TROPICAL SOILS

Experiments were conducted at the screen house of the Soil Research Institute (SRI), the Savanna Research Institute (SARI) laboratory and University for Development Studies, Applied Chemistry and Biochemistry laboratory, Navrongo Upper East Region Ghana. The objectives were to assess available and potentially available nitrogen (labile N) by extraction with 10.0 M NaOH in a simplified micro-diffusion technique using a locally constructed Mason-jar made from jam bottle. Tropical soils were used for the tests and the test crops were millet, rice and maize in a screen house. Below the maximum threshold, extracted labile N increased with increasing plant biomass yield of the three cereal crops. The method was also assessed for its ability to measure crude protein. It was found the alkaline extraction correlated significantly with conventional methods such as aerobic, anaerobic incubation, total Kjeldahl and N uptake methods (r of 0,896-0,9802; p < 0.01) that have been used to estimate N. There was also a positive response of increasing extracted N to increasing biomass yield in the crops used for the test. N extracted from the leguminous grains was linearly related to total Kjeldahl N and thus could be used to estimate crude protein. It was concluded that the simplified method of alkaline extraction of N could be used on farmers’ fields to estimate the quality of organic fertilizer. The apparatus could also be used to demonstrate how N is determined in school laboratories.