Response of Organic and Inorganic Fertilizers on Growth and Yield of Wheat at Kulumsa in Arsi Highlands of Ethiopia

Introduction

Wheat has been and continues to be one of the most important cereal crops in Ethiopia in terms of both area under cultivation and production [1]. The area under wheat cultivation was estimated at 1.67 million ha with an average production of 2543 kg ha-1 [2]. With the rapid increase in population and urbanization, the demand for wheat as a staple grain food is increasing. Though Ethiopia is among the largest wheat producer in sub- Saharan Africa, consumer demand far exceeds domestic production and wheat imports are costing the country millions of dollars in foreign exchange.

Depletion of soil fertility and poor crop management practices are among the major constraints responsible for the low productivity of wheat in Ethiopia [3]. The use of mineral fertilizers to avert soil fertility depletion in wheat production is still at suboptimal level [4]. Currently, 190,631 ton of organic and inorganic fertilizers have been used for the production of wheat in 2014 cropping season [2]. The mean fertilizer use for wheat of the country, 115 kg ha-1, was far below compared to the research recommendation of 250 kg ha-1 [5]. One of the major reasons behind the suboptimal use of inorganic fertilizers for grain crops is the costly price. Continuous production of crops against a backdrop of little fertilizer use over decades has aggravated the decline in soil fertility and crop yield [3, 6, 7].

The integration of organic fertilizers like vermicompost and conventional compost with inorganic sources may improve and sustain crop yields without degrading soil fertility status. Integration of organic and inorganic fertilizers improved the crop yield compared to fertilizers applied separately [7]. Integrated soil fertility management based crop production systems plays important roles in restoring soil fertility and availability of plant nutrients, enhancing crop growth and productivity [3, 8]. Therefore, the objective of this study was to determine the effect of integrated use of vermicompost, conventional compost and inorganic fertilizers on the yield and yield components of bread wheat.

Results and Discussion

The analysis of variance for yield and yield components of bread wheat are indicated in Table 3. Application of organic and inorganic fertilizers significantly affected most of the bread wheat parameters measured except for spike length, hectoliter weight and thousand seed weight (Table 3). Significant variations were observed on yield and yield components of bread wheat due year effect indicating temporal variations across cropping seasons.

The application of organic and inorganic fertilizers significantly (P<0.05) increased the mean grain yield of bread wheat (Table 3). The highest grain yield of bread wheat (4695 kg ha-1) was recorded from the application of half dose of the recommended rate of nitrogen and phosphorous from vermicompost and the remaining half dose from inorganic fertilizer (DAP and urea) (Table 4). This treatment gave grain yield advantage of 504 kg ha-1 compared to application of the whole dose of recommended rate of N and P from vermicompost alone (4191 kg ha-1). Application of the recommended dose of N and P from inorganic fertilizers produced 4677 kg ha-1 of bread wheat (Table 4). Application of half dose of the recommended rate of N and P from conventional compost and the remaining half dose from inorganic fertilizer gave 4640 kg ha-1 of bread wheat (Table 4). Application of half- half of the recommended rate of N and P from conventional compost and inorganic fertilizers gave grain yield advantage of 440 kg ha-1 as compared to application of N and P from compost alone (Table 4). Therefore, application of N and P from vermicompost or conventional compost alone did not bring significant increase of mean grain yield of bread wheat (Table 4) indicating the slow release of nutrients from organic fertilizer sources.

Integrated use of organic and inorganic fertilizers showed highly significant (P<0.001) increase in the biomass yield of bread wheat (Table 4). The highest biomass yield of bread wheat (13430 kg ha-1) was obtained from the application of the recommended dose of N and P from inorganic fertilizers followed by application of half-half dose of the recommended rate of nitrogen N and P from vermicompost and inorganic fertilizers (12509 kg ha-1), which were statistically similar (Table 4). Application of recommended rate of N and P from inorganic fertilizer gave biomass yield advantages of 3561 and 3464 kg ha-1 as compared to application of no input and N and P from vermicompost alone.

Integrated application of organic and inorganic fertilizers showed highly significant (P<0.001) difference on number of spikes m-2, plant height and number of seeds spike-1 of bread wheat (Table 3). The highest number of spikes (387) and plant height (89.8 cm) were obtained from the application of half-half dose of the recommended rate of N and P from conventional compost and inorganic fertilizer (Table 4). Application of full dose of N and P from either vermicompost or conventional compost or in combination to each other resulted in inferior plant heights. The slow release and unavailability of important nutrients from organic sources might be attributed to the shortest plant height. Higher number of seed spike-1 of bread wheat was obtained from application of recommended rate of N and P from inorganic fertilizer, and 33: 33: 33 % RR VC: RR C: RR IF (Table 2 and Table 4). The lowest number of seeds spike-

1was obtained from the application of no nutrients applied at all.

The mean grain and biomass yields of bread wheat in 2015 were statistically superior over 2014 cropping season (Table 4). This was mainly attributed to the rainfall condition, which was very high and low in 2014 and 2015, respectively (Figure 1). The very high rainfall condition in the cropping season (July to October) in 2014 might be resulted in excess moisture storage in the soil profile and affected the normal growth of bread wheat. Since the soil of Kulumsa is vertic-luvisol, the excess rainfall induced a sort of water logging problem; hence, resulted in underperformance of bread wheat roots and consequently reduced yield compared to 2015 copping season [9, 11]. Even though the rainfall condition in most of the main cropping season in 2015 was relatively lower than the long term average, the soil could conserve and efficiently utilize the available moisture; hence, it resulted in better yield.

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Conclusion

Integrated application of organic and inorganic fertilizers significantly increased the yield and yield components of bread wheat. The highest yield and yield components of bread wheat was recorded from the application of full dose of N and P from inorganic fertilizers alone (73/30 kg N/ P ha-1); half dose of the recommended rate of N and P from vermicompost (3.5 t ha-1; in dry weight basis) and inorganic fertilizer (37/15 kg N/P ha-1); and half dose of the recommended rate of N and P from conventional compost (6 t ha-1; in dry weight basis) and inorganic fertilizers (37/15 kg N/P ha-1). Application of the whole dose of N and P from vermicompost alone or conventional compost alone or in combination to each other did not bring significant yield and yield components increase of bread wheat.

In order to maintain soil fertility, reduce cost of inorganic fertilizers and sustain bread wheat production, farmers of the study area and similar agro ecologies are advised to make integrated use of organic (vermicompost or conventional compost) and inorganic fertilizers. Application of half dose of the recommended rate of N and P from vermicompost/ conventional compost and the remaining half from inorganic fertilizers has been advised as the top priority management option even though other alternatives are still available.