Abstract:
Bread wheat is one of the major food security crops in Tigray Regional State, northern Ethiopia. However, moisture stress and low soil fertility limits the production of bread wheat in the region. As a result, three field experiments were conducted in Enderta district in the 2013 and 2014 main cropping seasons with four key objectives. 1. To assess the impact of different rates and timing of nitrogen fertilizer application on the yield, quality, and nitrogen use efficiency of bread wheat varieties (Experiment one). 2. To elucidate the effect of organic and mineral NP fertilizer application on wheat productivity and selected soil chemical properties (Experiment two). 3. To evaluate the effect of different rates of nitrogen and supplemental irrigation on the yield, above ground biomass and water productivity (Experiment three), and 4.Toidentify economically optimum rates of the fertilizer treatments in the experiments. In the first experiment, there were 26 treatments comprising combination of four levels of nitrogen (23, 46, 69 and 92 kg N ha-1), three timing of N application (½ at sowing + ½ at tillering, ¼ th at sowing + ½ at tillering + ¼ th at anthesis, 1/3rd at sowing + 1/3 rd at tillering + 1/3 rd at anthesis), and two bread wheat varieties (Picaflor and Mekelle I), and 0 kg N ha-1 (control).The treatments were arranged in a factorial combination in a randomized complete block design with three replications. In the second experiment, there were 24 treatments that consisted of three bread wheat varieties (Picaflor, Paven 76, and Mekelle I) and eight fertilizer combinations [control, blanket recommended NP fertilizer (RNP) (41 kg N ha-1 + 46 kg P2O5 ha-1 , 10 t FYM ha-1, ½ of RNP + 10 t FYM ha-1, ½ RNP + 5 t FYM ha-1, 7 t ha-1 compost, ½ RNP + 7 t compost ha-1, and ½ RNP + 3.5 t compost ha-1. The treatments were arranged in randomized complete block design in a factorial arrangement with three replications per treatment. In the third experiment, there were 20 treatments consisting of four levels of supplementary irrigation (SI), viz: 0, 50 %, 75% and full 100% of the crop water requirement in the main plot and five nitrogen levels of 0, 23, 46, 69 and 92 kg N ha-1 maintained in the sub-plot. The treatments were arranged in a randomized complete block design (RCBD) in split-plot arrangement with three replications.Results from the first experiment showed significantly higher above ground biomass and grain yields of the crop, respectively, in 2013 cropping year (6871 kg ha-1 and 2775 kg ha-1) and in 2014 cropping year (8815 kg ha-1and 3695 kg ha-1) in response to the application of 69 kg N ha-1. The lowest aboveground biomass and grain yields, respectively, in 2013 cropping year (2740 kg ha-1 and 1072 kg ha-1) and in 2014 cropping year (4605 kg ha-1and1883 kg ha-1) were obtained in response to the application of 23 kg N ha-1. Maximum total N uptake 80.6kg ha-1and 95.8 kg ha-1 and apparent recovery efficiency of (74%,81%) was obtained at the rate of 69 kg N ha-1 at both seasons. The highest agronomic(25kg kg-1, 34 kg kg-1and nitrogen utilization efficiency 55, 78 kg kg-1 were recorded at 46 kg N ha-1 applied in three splits of 1/4 at planting, ½ at tillering and ¼ at anthesis. The highest grain protein concentration of 11.8 % in 2013 and 9.8% in 2014 was recorded in response to application of 69 kgN ha-1. The highest net benefit and marginal rate of return was xxiii obtained in response to the application of 69 kg N ha-1 and Picaflor was found to be the most productive variety. In the second experiment, yield and yield components of wheat significantly (P ≤ 0.01) responded to fertilizer application. Farm yard manure at 10 t ha-1 plus ½ RNP produce maximum productive tiller m-2 (298),kernel spikes-1 (41.84), spike length (8.25cm), thousand kernel weight (39.97g) and total above ground biomass yield (8618 hg ha-1). Combined application of 10 or 5.0 FYM t ha-1 plus20.5 kg N + 23 kg P2O5 ha-1increased grain yield by 185 and 170% while the combination of 7.0 or 3.5 t ha-1 compost plus 20.5 kg N + 23 kg P2O5 ha-1 increased grain yield by 159 and 148%, respectively over the control(no fertilizer) treatment.The acceptable marginal rate of return (712%) and the highest net benefit (37290ETB ha-1) was obtained from the variety Picaflor at the rates of 20.5 kg N + 23 kg P2O5 ha-1 +5 t ha-1 FYM. Application of 10 t ha-1FYM +20.5 kg N + 23 kg P2O5 ha-1increased soil organic matter, available phosphorus, and total nitrogen contents of the soil by 90, 88 and 133%, respectively, over the control treatment. It could be concluded that combined application of 20.5 kg N + 23 kg P2O5 ha-1 +5 t ha-1 FYM led to the optimum production of the crop and improved soil physicochemical properties to sustain crop yields in the study area. In the third experiment, application of 92 kg N ha−1 with 75% SI or 100% SI level increased tiller production by 94% and 92%, respectively as compared to the rain-fed treatment. Similarly, plants that received 100% SI with the application of 69 kg N ha-1 had their heights significantly increased by about 39%, spike length by 56%, kernel per spike by 51%, TKW by 47% and aboveground biomass yield by 340% as compared to no irrigation and nitrogen application. A maximum yield (4504.5 kg ha-1) was recorded from 100% SI combined with 92 kg N ha-1 and did not differ significantly with plots that received 69 kg N ha-1. Similarly, 100% supplementary irrigation level combined with 92 kg N ha-1 resulted in the maximum water productivity (7.99 kg ha-1 mm-1) but did not differ significantly with plots that received 75% SI with 69 kg N ha-1. The lowest yield (885 kg ha-1) and water productivity (2.15 kg ha-1 mm-1) were recorded for rain-fed and no nitrogen treatment. However, SI 100% with N rate of 92 kg ha−1 resulted in the most profitable yield (4504.5 kg ha-1). It could, thus, be concluded that under rain-fed condition, application of 69 kg N ha- 1 in three splits of ¼ at planting, ½ at tillering and ¼ at anthesis resulted in a profitable yield (3695 kg ha-1) and enhanced grain protein concentration (10.3 %), with the Picaflor variety being superior in its yielding ability. For the integrated use of mineral and organic fertilizer as well as wheat varieties under rain-fed production system, cultivating the Picaflor variety at the combined rates of 20.5 kg N + 23 kg P2O5 ha-1+5 t ha-1 FYM resulted in the most profitable yield (3865kg ha-1). However, the integration of 92 kg N ha−1 with supplementary irrigation of 100% resulted in the most profitable grain yield of the crop (4504.5 kg ha-1) in the study area.