Abstract

Girma Abera

In Sub-Saharan African countries crop production and productivity is primarily limited by soil fertility decline. In view of this, organic materials can be used as fertilizer source. However, little basic information is available on the quality of locally available organic materials and how to synchronize nutrient release with plant nutrient requirement and growth stages. To this effect, locally available organic materials such as residues of soybean (SB), cow pea (CP), haricot bean (HB), chick pea (CHP), maize, (M) and farmyard manure (FYM) were evaluated along with different inorganic fertilizers (Yaramila (YM) and Urea + Di-ammonium Phosphate (UrDp) were applied to soil samples to grow a maize variety-Gibe 2 as test crop. The maize allometric parameters, nutrient ratios (NRs), nutrient recovery (NRy) and mineral fertilizer equivalency (MFE) were used to assess the mineral fertilizer value (MFV) of organic materials. MFE of organic materials was estimated as the available mineral N and P out of the fraction of total nitrogen and phosphorous applied relative to chemical fertilizers supply. The results revealed that maize allometry, NRy and MFE were significantly (p<0.05) influenced by fertilizer sources. Organic materials amendment resulted in poor maize allometry, low nutrient uptake and recovery perhaps due to their slow release of nutrients and microbial immobilization of nutrients. Interestingly, MFE of organic materials amended ranged from -201% with CHP to 63% with FYM, reflecting that extensive variation exist in terms of their MFV. This portrays that CHP residue is the poorest quality that displayed highest immobilization, and about 200% soil nutrient deficit, while FYM is the highest quality material that exhibited net mineralization and contributes 63% of the mineral fertilizer value of YM. The results suggest that the allometric parameters, NRy and MFE are the best methods to assess the MFV of organic materials for crop production under tropical soil.