Integrated Effects of Vermi-compost and NPS Fertilizer Rates on Soil Chemical Properties and Maize Production in Bedele District, Western Oromia

Integrated plant nutrient management is the application of inorganic fertilizer in combination with organic fertilizer to maintain soil fertility and balance nutrient supply in order to boost up the crop yield per unit area. A study was conducted in Bedele District on farmers' fields to find out the combined effects of vermi-compost (organic fertilizer) and NPS (inorganic fertilizer) rates on soil chemical properties and maize production. The treatments consisted of three levels of vermicompost (0, 1.5 and 3 t ha -1 ) and three levels of NPS fertilizer (0, 100 and 200 kg ha -1 ). The experiment was laid out in RCBD design in factorial combination with three replications. laboratory analysis results of composite soil samples collected before sowing showed deficiency in soil chemical properties. However, analysis of variance of post harvest composite soil samples collected from each plot indicated significant differences on soil available P, OC, TN and CEC while, soil pH and exchangeable acidity showed positive improvement as compared to initial soil sample. The analysis of variance among the treatments showed significant differences (P ≤ 0.05) on almost all the maize characters tested. The highest and lowest maize grain yield (7932.1 kg ha -1 ) and (1944.4 kg ha -1 ) were obtained from the treatment combination of 3 t ha 1 vermi-compost with 200 kg ha -1 NPS and 92 kg ha -1 N, and control plot, respectively. However this combination was statically at par with the treatment combination of 1.5 t ha -1 vermi-compost with 200 kg ha -1 NPS and 92 kg ha -1 N, which gave maize grain yield (7577.2 kg ha -1 ). Therefore, the present study showed that combined fertilization of vermi-compost and NPS fertilizer enhanced maize productivity and soil fertility status in the study area; indicated that maize productivity in the study sites were reduced due to high demand for external nutrient inputs. Hence combined fertilization of 1.5 t ha 1 vermi-compost with 200 kg ha -1 NPS and 92 kg ha -1 N could improve maize productivity and soil chemical properties, and recommended for the study area (Bedele District) and similar agro-ecology. The result also showed that the soils of the study sites had poor chemical fertility and integrated soil fertility management practices can improve the current situation.


Introduction
The loss of soil fertility from continual nutrient mining by crop removal without adequate replenishment, combined with imbalanced plant nutrition practices, has posed a serious threat to agricultural production [1]. Continuous cultivation of soils for many years without replenishing the nutrients mined has negatively affected fertility and availability of nutrients. [2]. also stated that cultivated weathered soils commonly suffer from multiple nutrient deficiencies, and nutrient balances are generally negative. The low nutrient levels in the soil are caused by crop removal of nutrients from the soil, little or no fertilizer application, and total removal of crop residues from the farmland and burning. Nowadays, due to increasing population pressure and shortage of land, deforestation and cultivation activities are being carried out on steep slopes, which accelerate soil erosion [3,4]. Moreover, the shortage of land for production of food crops has eliminated the practice of fallowing and crop rotation. Furthermore, shortage of grasslands (grazing areas) has forced the farmers to remove crop residues for animal feed. These lead to agricultural soil degradation with detrimental effects on the physical, chemical and biological properties of soils [5].
Soil fertility and functioning must be restored to provide sustainable farming systems. As alternative, solutions for increasing soil organic matter have been proposed. [6,7] recommended regular inputs of organic amendments to soil while other authors advocated the use of improved fallows to restore organic matter to soil [8,9]. These agricultural management methods are known to enhance the stock of soil carbon [10]. It is well established that organic matter plays a central role in maintaining key soil functions and is an essential determinant of soil fertility and resistance to erosion. Several authors have found that organic inputs increase soil microbial biomass [11,12] and enzyme activities [13,14]) and enhance microbial activity [15]. The application of organic amendments can, therefore, affect the activity, structure, diversity and function of soil microorganisms, which play a key role in soil processes to a greater extent.
Vermi-compost is the recently organic fertilizer in supplementing chemical fertilizers for sustainable development of agriculture [16]. It is produced through the interaction between earthworm and microorganism by the breakdown of organic wastes. It is a stabilized, finely-divided peat-like material with a low C: N ratio and high water holding capacity that constitute a source of plant nutrition which is released gradually through mineralization whenever the plant needs it [17]. It is a material that characterized by high porosity, aeration, drainage, water holding capacity and microbial activity [18]. Vermi-compost can influence the growth and productivity of plants significantly [19]. It increase soil organic carbon, nitrates, phosphates, exchangeable calcium and some other nutrients for plants (Orozco et al., 1996). It increases soil Cation Exchange Capacity (CEC) and crop yield [20]. The available nutrient status of soil was greatly enhanced by the application of vermicompost as an organic source [21]. Vermi-compost enhanced phosphorous concentration and uptake in soil, increasing the solubilisation of phosphorous either by microorganism activation with excretion of organic acids likes citric, glutamic, tartaric, succinic, lactic, oxalic, malic and fumaric [22]. It can improve physical, chemical and biological and processes of soil which have their bearings on plant's growth [23].
On the other hand, inorganic fertilizers overcome soilfertility problems and responsible for increasing large partof worlds food production [24]. Increment of crop yield from 30 to 50% has resulted from application of commercial fertilizers [25,26]. Crop yields in the developed world are high and agricultural soils have high fertility status due to intensive use of fertilizers [27]. This implies that using chemical fertilizer plays significant role in increasing food production to meet the demand of the growing world population. Similarly, Vermi-compost is increasingly considered in agriculture as a promising alternative to chemical fertilizers. However, the effects of vermi-compost either alone or integrated with chemical fertilizers, on the crop productivity is not yet fully understood. Therefore, integrated plant nutrients management can lessen this problem and can be suitable for any farming system and socio-economic conditions [28]. Integrated plant nutrient management is the application of inorganic fertilizer in combination with organic fertilizer to maintain soil fertility and to balance nutrient supply in order to boost up the crop yield per unit area [29][30][31].
Moreover, Ethiopia has realized that agricultural soils commonly suffer from multiple nutrient deficiencies, and nutrient balances are generally negative, and an effort has been made to increase soil fertility status; among which vermi-compost (organic fertilizer) is one of it. Similarly vermi-worms are distributed to local farmers' and they started producing vermi-compost. However, in the study area there is no information on the combined use of vermi-compost and chemical fertilizer for maize production. Therefore, the objective of the study was to find out the combined effects of vermi-compost (organic fertilizer) and NPS (inorganic fertilizer) rates on soil chemical properties and maize production in Bedele District.

Description of the Study Area
The study was conducted on three farmers' fields in Bedele District of Buno Bedele zone in 2019 main cropping season. Bedele District is located at 08°14'28.6"to 08°37'52.8"N and 036°13'22.0" to 036°35'09.1" E. The 18 years weather information at nearby study area (Ethiopian Metrology Agency Bedele District Branch) indicated that a uni-modal rainfall pattern with average annual rain fall of 1945 mm. The rainy season covers April to October and the maximum rainfall is received in the months of June, July and August. The minimum and maximum annual air temperatures are 12.9 and 25.8.0°C, respectively, The predominant soil type in southwest and western Ethiopia in general and the study area in particular, is Nitisols according to the [32] soil classification system. Its vernacular name is "Biyyee Dimmaa" meaning red soil. On the average, the soil is deep and relatively highly weathered, well drained, clay in texture and strongly to moderately acidic in reaction. Nitisols are highly weathered soils in the warm and humid areas of the west and southwest Ethiopia [33].

Soil Sampling and Analysis
Composite surface soil samples (0-20) cm depth were collected from each experimental sites before sowing and intensive soil samples were collected from each experimental plot after harvest to analyze soil pH (H 2 O), exchangeable acidity, available P (Olsen), (OC%), (TN%), and CEC. The collected soil samples were prepared and analyzed following standard laboratory procedures at soil analysis laboratory of, Bedele Agricultural Research Center.

Treatments, Experimental Design and Procedures
The treatments consisted of three levels of vermi-compost (0, 1.5 and 3 t ha -1 ) and three levels of NPS fertilizer (0, 100 and 200 kg ha -1 ) were arranged in randomized complete block design (RCBD) in a factorial combination with three replications. The total number of treatment were nine. The gross plot size was 12m 2 (3m x 4m) that accommodated five maize plants rows.
Hybrid maize (BH 661) which is high yielder as compared to other improved maize varieties in the study areas was used as a test crop in the District, that was planted in rows with spacing of 80 cm between rows and 25 cm among plants within a row. The experimental fields were prepared by using oxen plow in accordance with conventional farming practices followed by the farming community in the area where, the fields were plowed four times., and treated with lime for soil pH less than 5.5, and the amount of lime needed per hectare was calculated based on the formula LR = Ex. acidity*1.5*10 kun ha -1 . Full dose of vermi-compost and NPS fertilizer as per the treatment and onehalf of N was applied at sowing. The remaining one-half of N was top dressed at 35 days after planting in the form of urea. The field was kept free of weeds by hand weeding during the period of the experiment. All other recommended agronomic management practices disease and insect pest control were done.
Finally, days to 50% tasseling, biomass and grain yields were collected. Data on plant basis was recorded from the three central rows out of the five rows per plot. The collected data was subjected to analysis of variance using SAS software. Mean separation was done by LSD..

Effects of Vermi-compost and NPS Fertilizer Rates on Soil pH, Exchangeable Acidity, Available P, OC, TN, and CEC Status After Maize Harvest
Post harvest soil pH, exchangeable acidity, available P, OC, TN, and CEC are presented in (Table 1). The results indicate that there were no significant (P < 0.05) differences in soil pH and exchangeable acidity among the different vermi-compost and NPS fertilizer rates. The treatments were statistically similar, however, the greatest positive pH value (5.20) changed from the initial pH of 4.90 was recorded for vermi-compost rate at 3 tha -1 and no NPS fertilizer. The lowest negative pH changed from the initial soil pH was recorded for control treatment which gave pH value of 4.91. Whereas, exchangeable acidity decreased from 0.95 to 0.27 at 1.5 tha -1 vermi-compost and 100kgha -1 NPS fertilizer rates. The status of soil pH and exchangeable acidity were improved in this study indicated that, addition of lime and Vermi-compost to the experimental sites were effective in increasing soil pH, which realized that soil pH is considered a master variable in soils as it controls many chemical processes that take place. It specifically affects plant nutrient availability by controlling the chemical forms of the nutrients.
The results also indicate that there were significant (P < 0.05) difference in soil available P, OC, TN, and CEC. The status of soil available P after harvest was greatly enhanced as compared to initial P before sowing (Table 1), indicated that Vermi-compost enhanced phosphorous concentration and uptake in soil, increasing the solubilisation of phosphorous either by microorganism activation with excretion of organic acids likes citric, glutamic, tartaric, succinic, lactic, oxalic, malic and fumaric [22]. Plants only absorb approximately 20-30% of P in applied fertilizers each year [34]. In general a small proportion of applied P is immediately taken up by the plants and the remaining P accumulates in the soil, which is potentially available for uptake by crops in subsequent years. Vermi-compost increases soil organic carbon, nitrates, phosphates, exchangeable calcium and some other nutrients for plants [35]. Vermi-compost increases soil Cation Exchange Capacity (CEC) and crop yield [20]. Cation exchange capacity is highly correlated with organic carbon (OC) content of the soil, which is in turn, is affected by different soil management practices such as intensive cultivation, fertilization, and changes in land use [36]. Cation exchange capacity increases with increasing soil OM [37]. It is strongly affected by the nature and amount of mineral and organic colloids present in the soil. Thus, CEC measurements are commonly made as part of the overall assessment of the potential fertility of a soil, and possible response to fertilizer application [38]. In conclusion the available nutrient status of soil was greatly enhanced by the application of vermicompost as an organic source [21].

Mean Days to tasseling of Maize (BH 661) Under the Effect of Vermi-compost and NPS Fertilizer Rates
The analysis of variance for days to tasseling revealed significant variation due to main effect of NPS fertilizer rates. However, application of vermi-compost rates did not show significant effect on days to tasseling. Vermi-compost can influence the growth and productivity of plants [19]. Concerning interaction effect of vermi-compost and NPS, the highest days to tasseling of 92.3 days was obtained with the un fertilized treatment, whereas the lowest (88.2 days) was obtained with the combination of 1.5 t ha -1 vermi-compost and 200 kg ha -1 NPS (Table 2). Where, means followed by the same letters are not significantly different at (P≤0.05), VC =vermi-compost, t=ton, ha=hectare, NPS= (nitrogen, phosphorus, sulfur), kg=kilogram, DH = days to headings, CV= Coefficient of variation, LSD= Least significant differences.

Mean Biomass Yield of Maize Under the Effect of Vermi-compost and NPS Fertilizer Rates
Biomass yield was significantly (P < 0.05) affected both by the main effects and the interaction between these factors (Table 3). This might be due to adequate quantities and balanced proportions of plant nutrients in vermi-compost supplied to the crop as per its need during the growth period resulting in favorable increase in yield attributing characters [39]. The effect of NPS fertilization on maize biomass yield was found to be significant (Table 3). Biomass yield increased consistently with NPS rates where the maximum biomass yield (23366.8 kg ha -1 ) was obtained from the application of the highest NPS rate (200 kg ha -1 NPS) followed by 16386.3 kg ha -1 which was obtained from 100 kg ha -1 NPS and the minimum (9940.8 kg ha -1 ) was from the control plot (Table 3) Generally, biomass yield increased with increasing application rates of both vermi-compost and NPS fertilizer and decreased with the application of the minimum rates of these nutrient sources. Vermi-compost can influence the growth and productivity of plants significantly [19]. Moreover, the interaction effect of these factors also revealed that the combinations of higher rates of both the organic and inorganic nutrient sources gave significantly higher biomass yield of maize. This indicated that, vermi-compost plays a major role in improving growth and yield of different field crops, vegetables, flowers and fruits [40].  Table 4 presents the means of maize grain yield as influenced by different application rates of NPS and Vermicompost. The analysis of variance indicated significant (P<0.05) grain yield differences due to the application of vermi-compost, NPS and their interactions. Vermi-compost is the recently organic fertilizer in supplementing chemical fertilizers for sustainable development of agriculture [16]. Increasing NPS levels from 0 to 200 kg ha -1 showed linear and consistent yield increment. The average maize grain yield for the NPS treatments ranged from 2649.2 to 7443.4 kg ha -1 NPS with a yield increment of 26 to 74% over the control treatment, respectively. Increasing vermi-compost rate didn't show significant grain yield differences except control (Table 4).

Mean Grain Yield of Maize Under the Effect of Vermi-compost and NPS Fertilizer Rates
Concerning the interaction effect of vermi-compost and NPS, the highest grain yield (7932.1 kg ha -1 ) was obtained from the combination of 3 t ha -1 vermi-compost and 200 kg ha -1 NPS, however statically at par with 1.5 t ha -1 vermicompost and 200 kg ha -1 NPS. The lowest (1944.4 kg ha -1 ) was obtained with the un fertilized treatment (Table 4). The highest yield for the interaction effect could be due to vermi-compost promotes better root growth, nutrient absorption and improves nutrient status of soil, both macro-nutrients and micro-nutrients [41]. The growth and nutrient status of crops have revealed a positive effect on plant nutrition, photosynthesis, chlorophyll content and nutrient content of different plant components namely roots, shoots and fruits [42]. In conclusion Vermi-compost is the recently organic fertilizer in supplementing chemical fertilizers for sustainable development of agriculture.

Conclusions and Recommendation
Integrated nutrient management for crop production requires that quantitative information on all nutrient sources be made available. Organic fertilizers maintains soil health, improves soil nutrient exchange and it typically mineralized within only a few cropping seasons to obtain a sustainable and stable increase in yield while, the inorganicfertilizer is the immediate source for crop. One test to evaluate the effects of organic nutrient sources on soil fertility is obviously to measure yields over the long-term, because it takes years for the yield to consistently reflect improved soil fertility status. This presumably has been reflected on the soil parameters in the current study. Laboratory analysis results of soil samples collected before sowing showed deficiency in soil chemical properties. However, post harvest soil samples indicated that significantly difference and positive increment on soil fertility status tested.. The analysis of variance among the treatments showed significant differences on maize characters tested. Accordingly, combined fertilization of vermi-compost and NPS fertilizer enhanced soil fertility status and maize productivity in the study area; which indicated that maize productivity in the study sites were reduced due to high demand for external nutrient inputs. In conclusion, based on the data obtained from this study combined fertilization of 1.5 t ha 1 vermi-compost with 200 kg NPS ha -1 fertilizer and 92 kg N ha -1 are recommended for maize production to the study area (Bedele District) and similar agro-ecology. To sustain and/or improve the current unbalanced fertilizer application and soil mining of the study sites, precautionary actions such as adopting sustainable soil fertility replenishment strategy, soil conservation practices, lime application and avoiding unbalanced fertilizers can help to rebuild the soil conditions to increase crop productivity. Further researches have to be continued to recommend rate, time and method of combined application of vermi-compost and NPS fertilizer for major crops grown in this region.