Effect of organic and inorganic fertilizer application on improvement of degraded grazing land in the central highland of Ethiopia

Fekadu Nemera, Zewdu Kelkay Tessema¹ and Abule Ebro²

Adami Tulu Agricultural Research Center, PO Box 35, Ziway, Ethiopia
tessemazewdu@gmail.com
¹ School of Animal and Range Sciences, Haramaya University, PO Box 138, Dire Dawa, Ethiopia
² International Livestock Research Institute (ILRI) PO Box 5689, Addis Ababa, Ethiopia

Abstract

An experiment was conducted to evaluate the forage yield and quality of the natural pasture in degraded grassland through the application of chemical fertilizer, cattle manure, wood ash and lime at Meta Robi district of west Shoa zone in the central highland of Ethiopia, from June to October 2015, The study was carried in a randomized complete block design (RCBD) with three replications.

Application of organic fertilizers such as cattle manure and wood ash increased the botanical composition of herbaceous legumes over grasses; whereas, chemical fertilizer application increased the botanical composition of grasses and total DM yield production of the grassland. Cattle manure application increased crude protein and IVDMD contents of the grasslands as opposed to chemical fertilizer application.

Accordingly, for immediate soil fertility improvement of the existing grasslands, application of inorganic fertilizer is important. However, for sustainable improvement of the grasslands in the long-term, application of organic fertilizer, such cattle manure and wood ash are economical way of degraded grazing land improvement. Moreover, we recommend further studies on animal performance and feed intake to develop grassland-based feed resources for smallholder livestock producers in the highlands of Ethiopia.

Key words: botanical composition, dry matter, chemical fertilizer, grazing land improvement, natural grassland, wood ash

Introduction

Livestock sector play an immense role of contribution for Ethiopian economy, 30-40% of Agricultural Growth Domestic Product (ADP), 16-20% of national GDP and 14-16% of foreign exchanges comes from this sector (Gebregziabhare 2010). However, the contribution of the livestock sector is very low in Ethiopia in relation to the dynamic growth of human population and the high demand for livestock products (e.g., meat and milk), due to inadequate nutrition (Mekoya et al 2008). Therefore, increasing the livestock products are highly required to bridge the gap between the rapidly growing human population and the demand for livestock products in the country.

The natural pasture, which accounts about 25% of total landmass of the country, contributes about 57% of the feed resources for ruminants (Ulfina 2013). Moreover, grazing on communal and/or private grasslands are the dominant sources of ruminant feeds in the central highlands of Ethiopia (Getnet 1999). However, the productivity of the grasslands in most parts of Ethiopia is extremely low (Ulfina 2013), due to seasonal fluctuation of rainfall and poor grazing land management, conversion of grazing lands in to crop lands, as a result of increased human population (Yadessa et al 2016). In addition, the available grazing lands are also overgrazed and unproductive due to continuous heavy grazing and mismanagement of grazing lands (Abule 2015), leading to low dry matter (DM) yield, which results critical shortage of animal feed, below the maintenance requirement of livestock throughout (Tessema et al. 2010; Yadessa et al. 2016).

Soil fertility status of the grasslands is one of the factor that could contribute to the low productivity and quality of natural pasture (Adane and Berhan 2005; Yihalem et al. 2005). However, improvement of degraded grasslands could be achieved through the application of organic and/or inorganic fertilizer (Tessema et al. 2002; 2010). According to previous studies (Tessema 2005; Tessema et al. 2010) application of inorganic fertilizer can significantly improve the productivity and quality of grasslands in Ethiopia. Therefore, the objective of this study was to assess the effect of inorganic and/or organic fertilizer applications on the improvement of degraded grasslands in the central highlands of Ethiopia. In this study, we evaluated the effect of chemical fertilizer, cattle manure, wood ash and lime on botanical composition, biomass yield, chemical composition and in vitro dry matter digestibility of natural pasture.

Materials and methods

Experimental site

The study was conducted at Meta Robi district of western Shoa zone in the central highland of Ethiopia, during the growing season of the grassland, between June and October 2015. Meta Robi district is located at 13°59′ N, 38°28′ E at an altitude of 2473 m above sea level (Figure 1), about 110 km away from Addis Ababa, the capital of Ethiopia. The mean annual rainfall of the district is ranged between 503.2 mm and 1573 mm (from 2005 to 2015; Figure 2), and was highly variable among years. The main rainy season is from July to September. The mean annual minimum and maximum air temperatures of the experimental site were 15°C and 31°C, respectively (Figure 2). The study area was characterized mostly by flat land (60%), and the soil types are classified into Humic-Nitosols. The 0 –20 cm soil layer of the experimental site was characterized by a pH of 4.94, a total N content of 0.296%, available phosphorus (P) content of 1.16ppm/ kg, organic carbon of 0.98% and 20.4 ppm/kg of cations exchangeable capacity.

Prior to the start of this study, visual observations in most parts of the grazing areas of the study district were conducted. Then, based on similar soil type, slope, and uniform basal and ground cover of the grassland, a representative communal grazing area was selected and fenced for exclusion from livestock grazing prior to the study.

Figure 1. Location of the study area, Meta Robi district in western Shoa zone in the highlands of Ethiopia

Figure 2. Rainfall and temperature data of the study area, Meta Robi district in western Shoa zone in the highlands of Ethiopia, during the study period, 2015.

Experimental design and treatments

The study was conducted in a randomized complete block design with three replications. The treatments during the study included chemical fertilizer, cattle manure, wood ash and lime application, and the control (without both inorganic and organic fertilizer). Urea and Diammonium phosphate (DAP) was applied, as inorganic fertilizer, with 100 and 150 kg per hectare, respectively. Moreover, cattle manure, wood ash and lime were applied at a rate of 7.5, 3 and 2 t ha^-1, respectively (Anderson et al 2013; Asmare et al 2016 and Ritchey et al 2015). The chemical fertilizer and lime were acquired by purchasing from the local market, while both cattle manure and wood ash were collected from farmers in the study area. The plot size for each treatment was 4 m by 3 m, and the spacing between replications and plots were 3 m and 2 m, respectively.

The degraded grazing land was ripped to incorporate the treatments in to the soil and to prevent nutrients leaching before application of each treatment. After land preparation, plot for each treatment within each replication was prepared and laid out. Then, a combination of urea and DAP was applied on each plot and mixed using rack. Cattle manure was dissolved in to water and applied in the form of slurry. Wood ash and lime were slightly rinsed with water to prevent blowing and uniformly scattered over the plots (Mark et al 1990).

Data collection and sampling procedures

Botanical composition and dry matter (DM) yield

The vegetation in three randomly selected samples of 0.25 m² (0.5 m × 0.5 m quadrat) were harvested within each plot using a hand operated sickle, about 0.5cm above the ground. Immediately after harvesting, the total fresh weight of the pasture in each plot was measured using a sensitive balance, and then the sample in each plot was further classified into different botanical compositions based on biomass (grass, herbaceous legume and forbs), and each botanical component was weighed separately to determine the contribution of each component in the total DM yield of the pasture (ILCA 1990). Furthermore, all species were listed, recorded and identified based on their morphological, structural and floristic characteristics in each botanical component. For those species that were difficult to identify in the field, herbarium specimens were collected and transported to the Herbarium of Addis Ababa University, Ethiopia, for further identification. Nomenclature follows Fromann and Persson (1974), Edwards et al. (1995, 1997, 2000), Hedberg et al. (2003), and Hedberg and Edwards (1989, 1995).

The DM yield of each botanical component in each plot was determined by drying a representative sample in an oven at 70°C for 48 h until constant weight followed by weighing (ILCA, 1990). The DM yield of each botanical component was calculated separately and added together to provide the total DM yield of the plot, and the final DM yield was reported in tone per hectare (t ha^-1).

Chemical analyses and in vitro dry matter digestibility

Representative samples were taken from the whole harvested biomass (bulk sample) for each treatment (plot) in each replication, and oven-dried at 105 °C over-night. The dried samples were ground to pass through a 1-mm sieve, and were then stored individually in airtight containers for chemical analyses and in vitro dry matter digestibility (IVDMD) assessment. Each treatment was done in duplicate to increase the precision of the analysis. Ash was determined by igniting the samples in a muffle furnace at 550 °C overnight (AOAC 1990). Nitrogen and P were determined with an auto-analyzer (Chemlab 1984); CP was calculated as N × 6.25. Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were determined according to Goering and Van Soest (1970). Hemicellulose and cellulose were calculated as NDF minus ADF, and ADF minus acid detergent lignin (ADL), respectively. The IVDMD was determined by the modified Tilley and Terry system (Van Soest and Robertson 1985). All chemical composition and IVDMD analyses were carried out at the Holeta Agricultural Research Center, nutrition laboratory, Holeta, Ethiopia.

Statistical Analyses

The botanical composition (the proportion of grasses, herbaceous legumes and forbs), DM yield, chemical composition and IVDMD were subjected to analyses of variance (ANOVA) using Generalized Linear Model (GLM) procedures of SAS (SAS 2002). Mean separation was tested using the least significance difference (LSD). Proportional data were arcsine transformed to meet the assumption of normality and homogeneous variances prior to carrying out the ANOVA.

Results and discussion

Botanical composition

A total of 22 herbaceous species were identified in the experimental site, of which 15 were grasses, two were herbaceous legumes and eight were forbs (Table 1). Among the identified species, annuals and perennials consisted of 15 (72.7%) and 6 (27.3%), respectively, indicating the severe degradation level of the experimental site prior to this study. Moreover, 13 species were highly palatable, 5 species palatable and 4 species less palatable to ruminant animals. The herbaceous legumes identified were Trifolium species, which are highly palatable to ruminants according to Alemayehu (2004).

The application of both organic and inorganic fertilizer significantly (P<0.01) affected the grass, legume and forbs botanical composition (Table 2). Application of chemical fertilizer had a higher grass botanical composition (21.4%) followed by lime (10%) application in the degraded grazing land compared to application of cattle manureand wood ash, as well as the control (unfertilized) plot. On the contrarily,cattle manure and wood ash increased the herbaceous legume botanical composition, with 20.9% and 24.9%, respectively, compared to chemical fertilizer application and the control, whereas, application of lime increased herbaceous legume component by 5%. Higher forbs botanical composition (29.33%) was found in control plot, whereas chemical fertilizer, cattle manure, wood ash and lime decreased the forbs component. The highest proportion of grass component by application of chemical fertilizer might be due to quickly mineralize tendency of chemical fertilizers compared to organic fertilizer immediately after incorporation with the soil system, leading to release nitrogen that would fasten the growth of grass over legume since grass is highly responding to nitrogen fertilizer (Bumane 2010; Ahimad and Ibrahim 2013). Contrarily, the highest proportion of legume was recorded in wood ash and cattle manure application, which could be associated with the higher availability of phosphorous that would promote herbaceous legume, leading to suppression effect grass growth (University of Georgia 2013).The control plots recorded higher forbs and weeds due to the faster growth of annual weeds, which are a pioneer plant communities in degraded ecosystems.

Dry matter (DM) yield

The DM yield of the natural grassland was significantly affected (P<0.01) by the application of organic and inorganic fertilizer (Table 2).Chemical fertilizer increased DM yield by 65.3% and wood ash by 53.1%, whereas, cattle manure and lime increased by 49% and 42.1%, respectively compared to the unfertilized plot. Similar studies conducted in Turkey by Ahimad and Ibrahim (2013) showed hay yields of the grasslands increased by the application of chemical fertilizer. Other research finding by Cahiti et al. (2010) indicated that forage production increased by nitrogen and phosphorous fertilizer application. Application of wood ash is very quick to react in the soil systems and its effect can be easily realized during the year of its application. Thus, wood ash could improves nutrients availability, particularly, Ca, P, K, zinc, manganese, copper and boron, as well as other micro-nutrients, in the soil, which are increasingly become important to increase the growth and yield of natural pasture, more than the lime does (Tarlok 2007). The various mineral elements available in wood ash can be absorbed from the soil systems through plant growth and therefore improves nutrient supply to plants (Ohno 1992; Nkana et al. 2002; Saarsalmi et al. 2006; Isam et al. 2009; Asmare 2015).

The DM yield recorded as a result of the application of all the treatments was satisfactory compared to the control plot (Adane 2003; Alemayehu 2006). The study was in agreement with Tessema et al. (2010) that DM yield of the grass component increased with the application of nitrogen fertilizer in the north-western parts of Ethiopia. Moreover, Tessema (2005) reported that the application of nitrogen fertilizer significantly increased the total DM yield of the natural pasture. Even though chemical fertilizer increased the DM yield in the current study, it was lower than what was reported by Gezahegn et al. (2015) around Holeta, central highland of Ethiopia, which might be due to the difference in soil fertility, climatic factors (rainfall), and severity grazing land degradation prior to fertilizer application.

The proportion of the herbaceous legume was higher than the grass and forb components of the natural pasture under the cattle manure and wood ash fertilized grassland plots compared to the chemical fertilized grassland plots in the present study. However, the grass component of the natural pasture was higher under the chemical fertilized plots than cattle manure and wood ash (Table 2). This indicated that the growth of herbaceous legume component of the natural pasture was found to better with the application of cattle manure and wood ash than that of chemical fertilizer and lime in our study. Moreover, cattle manure application was recorded relatively a similar higher total DM yield of natural pasture with that of wood ash. This might be because o the fact that cattle manure composed of potassium and phosphorous minerals that could easily promote the growth of herbaceous legumes, and thus increase the nutritive value of the natural pasture sward (University of Georgia 2013). As a result, this could be a good opportunity for resource poor farmers that can still support CP and digestible DM yield of natural pasture above the maintenance requirement for ruminant animals by harvesting the grassland before these herbaceous legumes get disappeared.

According to previous studies (Boote et al.1996; Kagata et al. 1999; Søresen et al. 2003) the application of organic (cattle) manure interferes differently with plant growth and development than chemical fertilizer application. Because the beneficial effect of cattle manure application to pasture production is better growth and development of the herbaceous legume component in the pasture sward (Tessema et al. 2010) due to the provision of various elements and nutrients during mineralization processes of the manure. Herbaceous legumes are favored by manure and lime as opposed to grasses favored by chemical fertilizer such as NPK. This would significantly increase the biomass yield and improve the nutritive values of the natural pasture to livestock feeding under smallholder conditions in most developing countries of the world compared to the application of inorganic fertilizer, which is more expensive than manure. Accordingly, if cattle manure and wood ash are appropriately applied to natural pasture, they could allow the opportunity to eliminate the inorganic fertilizer application to natural pasture production in the form of green pasture grazing, hay production and silage making under smallholder famers conditions.

Chemical composition and in vitro dry matter digestibility

The application of chemical fertilizer had significantly affected (P<0.05) the DM content of the natural pasture in the study area, which is in agreement with the findings of Bumane (2010) and Ashagre (2008). The highly significant effect of chemical fertilizer on natural pasture might be due to the fact that grasses are more responsive to application of nitrogen fertilizer than organic fertilizers such as cattle manure in the first year of growth (Abdi et al. 2015a, b). The total ash content of natural pasture was also significantly affected (P<0.05) by the application of wood ash and lime compared to inorganic fertilizer application. This might be because of the fact that wood ash has inherently high mineral contents than that of inorganic fertilizer according to previous studies (Mijangos et al. 2005 and Wilson et al. 2010).

Application of cattle manure, wood ash and lime (P<0.01) had a higher crude protein (CP) contents of natural pasture compared with chemical fertilizer application (Table 3). Similarly, the IVDMD value of natural pasture was higher with the application of cattle manure followed by lime application in our study. This could be attributed due to the presence of high herbaceous legume botanical composition of the natural pasture reported under the cattle manure applied plots than chemical fertilizer applied plots in this study. According to Bumane (2010) and Min et al (2002) cattle manure application on natural pasture provide available nitrogen and phosphorous reasonable to increase the herbaceous legume components that could lead of a higher crude protein contents of the natural pasture.

However, the application of organic and inorganic fertilizer did not significantly affect (P>0.05) the NDF content of natural pasture in our study. This might be due to that fact that the NDF content of natural pasture is highly interconnected with the stages of growth or stages of maturity of the natural pasture than fertilizer treatments. According to Tessema et al. (2010), a higher stage of maturity of natural pasture becomes lignified, leading to a higher NDF contents. However, the application of organic and inorganic fertilizer significantly affected the ADF content of natural pasture in the present study. Moreover, chemical fertilizer highly affected the ADL contents of the natural pasture in our study. Previous studies (Minson 1990; Cahiti et al. 2010, Abdi et al. 2015a, b) indicated that application of nitrogen fertilizer at a higher level on natural pasture facilitates faster growth, and leading to lignifications of natural pasture at early ages of the pasture, mostly in tropical environments.

The application of cattle manure and wood ash on natural pasture reduces the dependence on chemical fertilizer and increase the growth, production and nutritive value of natural pasture if there is appropriate grass – legume combination because this would maintain the soil micro-organisms, particularly, rhizobial bacterial diversity (Annicchiarico et al. 2011), leading to sustainable soil fertility improvement of degraded grasslands. Moreover, herbaceous legumes produce less methane in the animal when fed and support better animal growth rate, indicating that cattle grow faster on grass-legume mixed natural pasture (mixed species with more legume components) than on pure grasses. Therefore, it is concluded that grassland in the central highlands of Ethiopia can be categorized as medium quality herbage with the addition of cattle manure and lime that could be used as a dry-season feed for ruminants under smallholder farmer’s conditions. Thus, natural pasture fertilization seems feasible for smallholder farmers to increase availability of livestock feed resources for dry season feeding but it is important that the economic valuation of natural pasture fertilization should be consider the production cost and estimated prices of native hay on local market.

Conclusions

• Application of organic fertilizers such as cattle manure and wood ash increased the botanical composition of herbaceous legumes over grasses; whereas, chemical fertilizer application increased the botanical composition of grasses and total DM yield production of the grassland.
  
  
• Cattle manure application increased the crude protein and IVDMD contents of the grasslands as opposed to chemical fertilizer application.
  
  
• For immediate soil fertility improvement of the existing grasslands, application of inorganic fertilizer is important. However, for sustainable improvement of the grasslands in the long-term, application of organic fertilizer, such cattle manure and wood ash are economical way of degraded grazing land improvement.
  
  
• We recommend further studies on animal performance and feed intake to develop grassland-based feed resources for smallholder livestock producers in the highlands of Ethiopia.

Acknowledgements

The authors acknowledged the International Livestock Research Institute and Oromia Agricultural Research Institute for financing the research, the district administration and the farmers for allowing the grazing land to undertake the research and Mr. Bediru Roba for his support towards identification of the grass and legume species.

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Received 10 December 2016; Accepted 29 January 2017; Published 1March 2017

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