Nitrogen use efficiency and wheat yield as affected by nitrogen source, rate and crop sequence on karu soil of River Nile State, Sudan

Three field experiments were conducted on "Karu" soils (fine, smectitic, hyperthermic, Chromic Haplotorrerts) at Hudieba Research Farm, Ed Dammer, River Nile State during the seasons 2001/02 and 2002/03. The main objective of this study was to test the N use efficiency (NUE) of three N fertilizers (nitrophoska (NPK), ammonium sulphate nitrate (ASN)) and urea and compare wheat crop performance and production on "Karu" soils. This is to increase wheat yield and to restore soil productivity. Two levels of nitrogen namely 40 and 80 kg N ha-I of the three tested fertilizers were used. The tested nitrogen fertilizers were manipulated to maintain similar nutrient content by adding the deficient macro and micronutrient in the required levels. As a result, two controls (ON) became necessary. The resultant eight treatments were set in a randomized complete block design with four replications. The wheat cultivar Wadi Elneil at a seed rate of 120 kg ha-I a s well as the fertilizers were broadcast on flat and covered with soil by ridging. In the first season, the wheat experiment was preceded by faba bean crop (FB/W). In the second season, two wheat experiments, onc experiment was on the same subplots of the first season experiment (W /W) and the second heading and maturity stages and analyzed for Nand P content. Results indicated that nitrogen application increased grain yield, biomass, number of spikes m-2, 10 head seed weight, 1000 seed weight, plant height, harvest index, plant N and total Nand P uptake. At the level of 80 kg N ha-I, NPK gave the highest wheat grain yield in both seasons and crop sequences followed by urea and then ASN with no significant differences between the last two N sources under FB/W crop sequence. At seedling stage and at any given N level, NPK produced the highest plant N followed by urea and then ASN under both crop sequences. Also, at 80 kg N ha-I, NPK produced the highest total Nand P uptake followed by urea and then ASN with no significant differences between NPK and urea under W /W crop sequence. Nitrogen use efficiency (NUE), a measure of the extent to which a crop transforms available N to economic yield, decreased with the increasing level of N applied under FB/W crop sequence except for NPK where it increased. However, under W/W crop sequence, the increase ofN level applied increased NUE for the different N sources. At the level of 80 kg N ha-I, NPK gave the highest NUE followed by urea and then ASN under both crop sequences. At any N level, ASN gave the highest residual soil N in the plough layer followed by urea and then NPK. Growing wheat after wheat decreased grain yield, biomass, harvest index, NUE and total N and P uptake compared to wheat after faba bean