Determination of NPS Fertilizer Rate Based on Calibrated Phosphorus for Yield of Bread Wheat in Wachale District, North Shewa Zone, Oromia, Ethiopia

Farmers are using NPS fertilizer rates in the area without any recommendation of crop response to the respective fertilizers This experiment was conducted to evaluate the effect of NPS fertilizer rate for higher yield of bread wheat in Wachale district. The experiment consisted six rates of NPS fertilizer rate supplemented with 92 kg N ha -1 laid out in RCBD with three replications. Improved variety of bread wheat Danda’a was used. The analyzed result indicated that, plant height and wheat grain yield were significantly (P<0.05) influenced by NPS fertilizer rate. The highest (94.56 cm) plant height was recorded from the application of 100% P-critical in NPS fertilizer rate and the lowest (63.62 cm) plant height was recorded from unfertilized plot. The highest (2833 kg ha -1 ) grain yield was obtained from the application of 100% P-critical in NPS fertilizer rate and the lowest (888 kg ha -1 ) grain yield was obtained from unfertilized plot. Partial budget analysis showed that the highest net benefit (53401.51 ETB ha -1 ) and marginal rate of return (MRR) (1093.80%) were obtained from the fertilizer application of 100% P critical in NPS fertilizer). Therefore, 100% equivalent rate of NPS fertilizer rate in relative to determined critical phosphorus supplemented with 92 kg N ha -1 for bread wheat could be recommended and thus soil test based crop response phosphorus fertilizer recommendation with 92 kg ha -1 of Nitrogen could be demonstrated and further scaled up for Bread wheat in Wachale district.


Introduction
Cereals are the most widely grown crops and comprise about 87.97% of total grain production in Ethiopia [6]. Wheat is one of the most important cereals in Ethiopia and it is one of the largest producers of wheat in sub-Saharan Africa. The area coverage and production of the crop in Ethiopia is estimated to be 1.7 million hectares and 4.8 million tons of grain yields, respectively. These accounts about 15.39% of total grain output in the country [6]. There are two types of wheat grown in Ethiopia: durum and bread wheat accounting 40 and 60% of production, respectively. Wheat production in Ethiopia are characterized by subsistence farming and mostly dominated by small holder farmers [6,13]. The national average productivity of wheat (2.7 tone ha) [6] is still lower than world's average (3.4 tone ha -1 ) [10]. Of the many reason for low productivity of wheat; decline of soil fertility, prevalence of disease, dependency on rain-fed traditional agriculture and low input including fertilizer application are the most important ones.
In order to tackle this soil fertility problem, the Ministry of Agriculture was conducting soil and plant nutrient survey to determine the key soil nutrient limitations along with importation of different blended fertilizers and micronutrients from abroad and test these against Urea (50 kg ha -1 ) and di-ammonium phosphate (DAP, 100 kg ha -1 ) for their impact on crop yield in different areas and crops. The results from both of these initiatives showed deficiency of 3 to 6 nutrients N, P, S, Zn, Mo and B. In most parts of the country and crops responded to the application of additional nutrient. Moreover, the plant analysis data from the same sites indicated that wheat plants were deficient in N, P, Zn and K [11]. Due to this, Ethiopia is moving from blanket recommendations for fertilizer application rates to recommendations that are customized based on soil type and crop. This is a move towards diversification and away from DAP and Urea, which have long been the only type of fertilizer imported for grain crops.
The farmers in most parts of the country in general and in the study area in particular have limited information on the impact of different types and rates of fertilizers except blanket recommendation. However, according to the soil fertility map covering over 150 districts, most of the Ethiopian soils lack about seven nutrients (N, P, K, S, Cu, Zn and B) [9]. [2] Reported that grain yield and yield components of wheat (100%) fully responded to applied nitrogen, 72.3% showed response to sulfur, 78% showed response to applied phosphorus on eighteen fields studied in central high lands of Ethiopia and strongly indicated sulfur deficiency along with its importance to include in balanced fertilizer formula. Apart from blanket recommendation of nitrogen and phosphorus, the effect of other fertilizers on yield and yield components of bread wheat and durum wheat are unknown in Ethiopia, even though new fertilizers such as NPS (19% N, 38% P 2 O 5 and 7% S) are currently being used by the farmers with blanket recommendation of 100 kg NPS ha -1 in Ethiopia.
Since, Ethiopia is moving from blanket recommendations to soil test based fertilizer recommendations, Fitche Agricultural Research Center was conduct a research to determine critical phosphorus concentration and phosphorus requirement factors for bread wheat in Wachale district, North Shewa Zone. However, the effect of NPS fertilizer rate was not determined for bread wheat in the study area. Thus, based on the determined Pc (9.5 ppm) and Pf (14.23), optimum NPS fertilizer rate determination was carried out in the study area with the objectives; to determine NPS fertilizer in relative to determined P-critical for bread wheat and to estimate the economically feasible NPS fertilizer rate for higher yield of bread wheat in Wachale district.

Description of the Study Area
The experiment was conducted in Wachale district of North Shewa Zone, Oromia, central high lands of Ethiopia. The district is located at 78 km of the capital Addis Ababa in the Northwest direction. The district is located between 9°25'2.13" to 9°48'44" North and 38°38'49.02" to 39°08'41" East. The altitude of the study area ranges between 1200 and 2880 (m.a.s.l). That means the districts have the three major classification of landform such as highland, lowland and midland. The mean annual rainfall of the area is about 1000 mm that ranges from 1000 to 1800 mm. The maximum and minimum annual temperature is 3°C and 25°C, respectively.
Major farming systems of Wachale district were mixed farming; cereal crop cultivation and livestock rearing. Livestock productions are the most important agricultural activity next to crop production in the district, which supports the traditional subsistence farming of cereal crops. The crops such as wheat, teff, beans, barley, Chickpea, Lentil, Pea etc are the major crop in the study area.

Site Selection, Soil Sampling and Analysis Methods
Bread wheat production potential kebeles (small administrative unit) were selected from the district. Accordingly, the 10 farmer's fields were selected based on their willingness to handle the experimental fields. Before planting, surface composite soil samples were collected from the field for analysis at a depth of 0-20 cm in zigzag methods. Soil samples were collected using Auger. The collected surface soil samples from the experimental field were air dried, grinded and allowed to pass through 2 mm sieve for further analysis in the laboratory. The collected soil samples were analyzed for the parameters of pH (H 2 O) in the suspension of a 1:2.5 soil to water ratio using a pH meter and Available P was determined by the Olsen's method using a spectrophotometer [14]. Then the farmer's field was selected based on the analyzed soil sample results in which the soil pH above 5.5 and available soil phosphorus below critical phosphorus (Pc) was selected for the experiments.

Experimental Design and Treatments
The experiment was carried out on 10 farmers' field for two consecutive years. The experimental field was arranged with a total of 6 treatments with a randomized complete block design (RCBD) in three replications. The recommended Nitrogen (92 kg ha -1 ) for the district was used. The gross plot size was 3m * 4m and the space between block and plot was 50cm. The net plot size was 2 * 2m. The required amount of seeds was weighed per plot by considering the recommended rate of wheat seed per hectare (150 kg ha -1  The determined P-critical value (9.5 ppm) and phosphorous requirement factor (14.23) was used to calculate the rate of fertilizer to be applied. Thus, Phosphorus fertilizer rate was calculated by using the formula given below; Rate of P applied= (Pc-Pi) * Pf Where Pc: Critical phosphorus concentration Pi: Initial available P Pf: Phosphorus requirement factor which was derived from the calibration study.

Data Collection
Bread wheat grain yield was harvested at the ground level from the net plot area. Then, plant height was measured at harvest. After threshing, grain yield were cleaned and weighed.
Economic data such as production cost (input cost), gross income and net income based on the current market price of the yield and input was recorded.

Economic Analysis
Partial budget analysis was done to identify economical feasibility among. The average open market price (Birr kg -1 ) of bread wheat, price of fertilizers was used for analysis. For a treatment to be considered a worthwhile option to farmer, the minimum acceptable rate of return (MRR) should be 100% [4], which is suggested to be realistic. This enables to make recommendations from marginal analysis. Marginal rate of return (MRR) were calculated by using the formula given blow;

Data Analysis
All data recorded and collected were subjected to the procedure of analysis of variance (ANOVA) using R software program. The comparisons among treatment means were employed by using of Least Significance Difference (LSD) at 5% significant level.

Soil Reaction and Available Phosphorus
The soil pH (H 2 O) of the study area was moderately to slightly acidic with the value ranged from 5.56 to 5.9 according to the ratings suggested by [15] (Table 1). Thus; the pH of the experimental soil was within the range for productive soils. The available phosphorus content of soils was low to medium with the value ranged from 7.24 to 10.39 ppm according to the rating given by [5]. Therefore, the soil of the study areas needs application of phosphorus containing fertilizers for crop production.

Plant Height
Mean plant height was significantly (P<0.05) affected by NPS fertilizer rate. The highest (94.56 cm) plant height was recorded from the application of 100% P-critical in NPS fertilizer rate supplemented with recommended Nitrogen. The lowest (63.62 cm) plant height was recorded from control (without fertilizer) ( Table 2). The result showed that plant height increased with an increased of NPS fertilizer rate supplemented by Nitrogen fertilizer (Urea). The increment in plant height might be due to increase in cell elongation and more vegetative growth attributed to different nutrient content of fertilizer containing NPS and the increasing of sulfur content caused a significant increase in wheat root and shoot growth as well as nutrient uptake. The sulfur deficiency results in stunted growth and reduced plant height [8]. This result is in line with results of [1,12,16] reported that increased application of blended fertilizer significantly increased plant height of bread wheat.

Grain Yield
Grain yield of bread wheat was significantly (P<0.05) influenced by NPS fertilizer rate. The highest (2833 kg ha -1 ) grain yield was obtained from the application of 100% P-critical in NPS fertilizer rate supplemented with recommended Nitrogen and the lowest (888 kg ha -1 ) grain yield was obtained from unfertilized plot ( Table 2). The results of this study indicated that, the mean of grain yield were increased with the increment of blended fertilizer rate. The highest grain yield at the highest NPS rates might have resulted from improved root growth and increased uptake of nutrients and better growth which enhanced yield components and yield of crops. This result is in agreement with [3,7,16] who reported that, the maximum grain yield of bread wheat was recorded at the highest application of blended fertilizer rate.

Partial Budget Analysis
The partial budget analysis showed that the highest net benefit (53401.51 ETB ha -1 ) and the highest marginal rate of return (MRR) (1093.80%) was obtained from the fertilizer application of 100% P-critical in NPS fertilizer with recommended Nitrogen fertilizer (92 kg N ha -1 ). The lowest net benefit (17760 ETB ha -1 ) was obtained from unfertilized plots ( Table 3). The MRR was indicated that bread wheat producers can get an extra of 10.94 ETB for 1.00 ETB investments in the NPS and N fertilizers application on the rates of 100% P-critical in NPS fertilizer with recommended nitrogen fertilizer (92 kg N ha -1 ). Therefore, application of NPS fertilizer at the rate of 100% P-critical in NPS fertilizer with recommended nitrogen fertilizer (92 kg N ha -1 ) for the production of bread wheat was more economically beneficial and recommended for Wachale district.

Conclusion and Recommendation
The productivity of wheat is declining e due to many reasons and among the low soil fertility is the most one. With the objective of solving this soil fertility problem, soil test crop response based fertilizer rate recommendation has been conducted across the country. The grain yield of bread wheat was influenced by NPS fertilizer rate whereby the results of this study clearly indicated that, the mean of grain yield were increased with the increment of NPS fertilizer rate. In addition, partial budget analysis has also shown a variation among the treatments and depicted that, application of NPS fertilizer at the rate of 100% P-critical in NPS fertilizer with recommended Nitrogen fertilizer (92 kg N ha -1 ) for the production of bread wheat was more economically beneficial and recommended for Wachale district.
Therefore, demonstration and further scale up of soil test crop response based phosphorus fertilizer recommendation with 92 kg ha -1 of Nitrogen demonstrated and further scaled up for bread wheat in Wachale district could be recommended and also the farmers could be used 100% NPS fertilizer rate in relative to determined critical phosphorus for bread wheat in the district.