Effects of moisture level and potassium on NH4+ nitrification and their influence on growth parameters and nutrient uptake of bread wheat (Triticum aestivum. L) grown on Typic Hapludert of central highlands of Ethiopia

Abstract

To understand the impact of moisture level and potassium on NH 4 + nitrification a greenhouse and laboratory studies were conducted using surface soil of Typic Hapludert (0–30 cm) of Ginchi, central Ethiopia. The treatments were two levels of moisture and three levels of fertilizer (six combinations replicated three times). The Typic Hapludert, which is dominated by smectite and contains relatively high illite, has 6.44% total potassium, high K-fixing (minimum of 4.89 and maximum of 69.88 mg/100 g soil) and buffering (45.05 mmol/) capacities and low potassium availability (2.26 cmol (+) kg soil). The soil contains significant amounts of potassium in the form of micaceous K. Eighty percent of the applied (NH 4 ) 2 SO 4 was nitrified and caused sharp increase of NO 3 under both moisture statuses between the 2 nd and 5 th weeks. Maintaining moisture at constant level could only delay nitrification, but could not stop nitrification process completely. Under all treatments the oxidation of (NH 4 ) 2 SO 4 into NO 3 - ions took place in a very short period. In treatments T 1 (without N and K fertilizers), T 3 (83 mg nitrogen) and T 5 (83 mg nitrogen, 37.5 mg K), which were watered every other day, 86-88% of (NH 4 ) 2 SO 4 was converted to NO 3 - within 15 days where as in T 2 (without N and K fertilizers), T4 (83 mg nitrogen) and T 6 (83 mg nitrogen, 37.5 mg K), which were moist to 60% water holding capacity of the soil every day, 34-44% of the applied (NH 4 ) 2 SO 4 oxidized to NO 3 - within 22 days. High moisture status has discouraged K assimilation without affecting nitrogen uptake significantly. However, Mg 2+ uptake was not affected under both water treatments. Application of potassium was found to shorten the time required for flowering.