Abstract
An experiment was conducted to determine the effects of vermicompost, inorganic fertilizers and their combinations on release of soil nutrients at different growth stages of wheat. A factorial combination of four levels of inorganic fertilizers (0, 33.33, 66.66, and 100% of the recommended NPK fertilizers) and vermicompost (0, 2, 4 and 6 t ha-1) were laid out in complete randomized design with three replications. Soil was collected before planting and after planting (at tillering, flowering and maturity stages of wheat) from each pot in order to determine dynamics of selected nutrients (NPK). The interaction between vermicompost and chemical fertilizers were not significant for NPK contents of the soil at all growth stages except phosphorus at heading stage. In all cases, highly significant increases in total N, available P and K in the soil were observed due to the increasing rates of main effect vermicompost or inorganic fertilizers during all growing periods. The highest available as well as total contents of NPK in the soil were found at tillering stage. This initial increment at tillering stage for both factors showed a declining trend later at heading and maturity stages. However, the observed decline was in exception for vermicompost applied at 6 t ha-,1 which maintained highest level of available P and K and 4 t ha-1 which continued mineralization of K up to heading stage. In general, application of 6 ton vermicompost per hectare was found proportional with the full dose of the recommended fertilizers in supplying NPK for wheat crop. Therefore, building up the total as well as available NPK to higher levels up to heading stage can bring maximum nutrient uptake and yields of wheat. Key words: Growth stages, mineralization, nutrient availability, nutrient decline.
Highlights
In Ethiopia, the major constraint to agricultural growth and food self-sufficiency for a long period is the decline in soil fertility
Regardless of a five times increase in fertilizer application in Ethiopia, national cereal yields have only increased 10% since the 1980s (Gete et al, 2010), while relative benefits of chemical fertilizer application have decreased over time
Application of inorganic fertilizers as well as vermicompost at low levels have a limited capacity in supplying NPK, which might not line up with the trend of wheat nutrient uptake
Summary
In Ethiopia, the major constraint to agricultural growth and food self-sufficiency for a long period is the decline in soil fertility. Loss of ammonium from urea due to leaching and volatilization during two to three weeks after application (Jones et al, 2007), fixation of phosphorus with Al/Fe oxides (Lungmuana et al, 2013) and potassium with interlayer of clay mineralogy (Najafighiri, 2014) were reported after the addition of inorganic fertilizers. Such losses could exhaust the pool and available stock of certain nutrients and brought a question whether they could support plant life until the maturity stage
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