Rehabilitation of degraded pasture land through application of urea and slurry: the case of Ayba pasture land, southern Tigray, Ethiopia

Tesfay Atsbha, Awet Estifanos¹, Solomon Wayu, Temesgen Tesfay and Adhanom Baraki

Alamata Agricultural Research center, P.O.Box 56, Alamata, Ethiopia
¹ Mekelle Agricultural Research Center, P.O. Box 258, Mekelle, Ethiopia
aweyetir@yahoo.com

Abstract

The experiment was undertaken at Emba Alaje District, Ayba Peasant Association (PA) for two consecutive years, which is 2013 to 2014, to evaluate forage yield of the natural pasture through application of urea and slurry and third control one. A factorial RCBD design replicated three times with two factors and three levels were used. Each treatment was allocated to 25m² in both years. Partial budget analysis, dominance analysis and marginal rate of return were calculated to compare treatments economic benefits.

Seven grasses, five annual legumes and two other herbaceous species belonging to different families were identified in all the plots. Dry matter yield (DMY) significantly increased by application of urea over the application of slurry and the control. The relative proportion of grass, and legumes reached highest and significant by urea application. The effect of years was also only significantly varied for DMY. The interaction effect of fertilization with years was significantly different for all the parameters with the highest result being for application of urea except for legumes and other plant species composition. However, application of slurry is an economical way of degraded pasture land improvement and improves grass-legume species composition.

Key words: botanical composition, dry matter yield, grazing land fertilization, grazing land rehabilitation, natural pasture land and species composition

Introduction

Livestock production is an integral part of the subsistence crop-livestock systems of the Ethiopian highlands. It is a source of draught power, manure and transport to support the crop sector. It is also a source of cash, nutrition and asset for rural com7munities. One of the major constraints to livestock productivity is lack of feed, both in quality and quantity (Tilahun et al 2005). Natural pasture and crop residues are poor in quality and provide inadequate protein, energy, vitamins and minerals (Daniel 1990). Thus, the existing feed resources do not meet the nutrient requirements for growth and reproduction of animals and the herbage yield and nutritional quality of natural pasture is generally low (Adane and Birhan 2005).

In the Ethiopian highlands most pasturelands have suffered encroachment of crop production as a consequence of the growing human population. The increase in human population and the decline in land productivity demanded an expansion in arable land that led to a reduction in natural pasture and browse (Alemayehu 1997). An important part of efficient livestock production is ensuring sufficient grass for both hay and pasture. Proper nutrient management in pastures will increase forage yields. This is especially noticeable when the pastures are in poor condition, with the forage plants stressed from over utilization. With good soil fertility and fertilizer management, the productivity of many hay and pasture fields can be greatly improved (Ross 2005). Proper management of the fertility improves the vigor of the forages, allows them to compete with undesirable plants (weeds), and improves overall yield (Howard 2010). However, low soil nutrient levels often limit forage production.

Most grazing lands in Tigray are poorly managed and are over utilized. To revert these situation different efforts has been exerted. One of the most viable and simple management interventions to prevent the severe feed shortage is to improve the quality and quantity of the natural pasture through employing improved management and conservation practices. However, limited attention has been given to soil fertility improvement practices. Therefore, the main purpose of this study was to determine better type of fertilization among inorganic and organic sources under controlled environment for rehabilitation of degraded community grazing land.

Materials and methods

Study area

The study was conducted at the highland of southern zone of Tigray, Emba alaje district, Ayba PA. The altitude of the area is 2350 masl with annual average rainfall of 912 mms and mean daily temperature ranging between 9–23 ºC. The rainfall is bi-modal with the belg rain (short rains) occurring in March to May and the meher (main season) rains lasting from June to September. Major crop such as sorghum, teff, maize, wheat, barley, bean, linseed, onion, paper, cabbage, fruits are grown in the study area (Girmay Tesfay et al 2014). Natural pasture is the major feed source in the area.

Experimental Design

The study was conducted using a factorial two by three in randomized complete block design replicated three times. The treatments for the study were control, urea and slurry and the amount of urea and slurry that are used in the experiment was 150 kg and 8 ton per ha respectively. The plot size consisted of an area of 25 m2 (5m x 5 m) and the space between block and plot was 1m. The total experimental area had an area of 289 m2 (17 m x17 m) the natural pasture was enclosed from July to September. The determination of species composition and harvesting was done at first week of December each year.

Sampling Procedures

The vegetation from each treatment was sampled using a quadrant of 0.25 m² (0.5 m x 0.5 m) size during a predetermined sampling period. The material was harvested with a sickle at a height of >10 cm above ground. The quadrant was randomly thrown three times per plot and the average weight of the three harvests per plot was used for determination of pasture yield and quality. Following harvesting the forage samples from each plot were weighed, labeled and air dried under shade. For determination of species composition, forage samples were harvested at the end of the day (90 days) and samples were weighed immediately and hand-sorted into botanical components of grasses, legumes and others. The DM yield of each plot was determined by drying a representative sample in an open air and the final yield was calculated in tons per hectare.

Measurements

Botanical composition

The botanical composition with regard to relative proportion of the grasses, legumes and other herbages in the treatment plots on weight basis was determined by relating the weights of each group to the weight of the whole samples. Identification of species was undertaken in situ by using an illustrated field guide of Froman and Persson (1974) for grasses and legumes.

Pasture yield

The pasture yield was determined on dry matter basis by harvesting forage sample by using a quadrant of 0.25 m² (0.5 m x 0.5 m) which was randomly thrown three times per plot. The average weight of the forage in the quadrant was used and extrapolated in to dry matter yield

per hectare (t/ha). Forage samples within the quadrant area were harvested with a sickle and weighed immediately. Sub-samples representing 10% of the whole forage samples harvested from the treatments were taken for determination of DMY.

Partial Budget Analysis

Partial budget analysis, dominance analysis and marginal rate of return were calculated to determine the profitability of application of fertilizers according to the procedure of Upton (1979). The economic analysis included the variable costs and benefits for the calculation. The gross field benefit per day was calculated by dividing the final sell of the biomass. Net Return (NR) or net benefit was calculated as the amount of money left when total variable costs (TVC) are subtracted from total returns or gross field benefit (TR):

NR = TR-TVC

The dominance analysis or the change in net income (ΔNR) was computed as the difference between the change in total return (ΔTR) and the change in total variable costs from the control (ΔTVC):

ΔNR = ΔTR – ΔTVC

The marginal rate of return (MRR), which measures the increase in net income (ΔNI) in relation with each additional unit of expenditure (ΔTVC) normally expressed as a percentage:

MRR= ΔNR/ ΔTVC

Statistical Analyses

The data obtained from the experiment was subjected to analysis of variance using the General Linear Model Procedure of SAS (SAS 1998). Significant treatment means was separated using Tukey HSD.

Results and Discussion

Botanical Composition

Natural pastures are composed of grasses, legumes, sedges, and other heterogeneous plants in various families, which could be herbaceous or woody forms (McIllroy 1972). Forage species of natural pasture that have been identified at the experimental site is presented in Table 1. Seven grasses, five annual legumes and two other herbaceous species belonging to different families were identified in all the plots. The majority of grass species identified were (Melinis) Keyh saeri, (Cynodon) Tahag, (Eleusine) Rghe and (Pennisetum)) Ayder, and the legumes that were identified include (Trifolium tembense) gurdimakuya, (Trifolium rueppellianum) chewchawe and (Trifolium campestre) effel. Most forage species identified in this study had similarities with previous reports on forage species composition in the highlands of Ethiopia, indicating that the high lands were rich in pasture composition, particularly indigenous grasses and legumes (Kidane 1993; Adane 2003; Tessema 2003; Yihalem 2004).

Effect of urea and slurry application on herbage yield and species composition

The different species composition of the natural pastureland is a desirable attribute in terms of pasture quality, quantity and persistence. Hence, the presence of desirable perennial and annual grasses species in the study area would indicate the degree of persistence of these species against recurrent drought, frost and high pasture pressure consistent with the harshness of the prevailing climatic biotic factors (Ashagre Abate 2008).

Dry matter yields were significantly different among all the treatments and higher results were obtained for application of urea, followed by slurry and the control one. This is in agreement with results of Adane (2003) and Teshome (1987). Similarly, there was significantly higher grasses species composition between application of urea and the rest of the treatments. However, non-significant result was obtained for composition of grasses between application of slurry and the control one. Unlike the grasses species composition, the species composition for legume was found to be significantly different among all the treatments, with higher being for application of urea. All the treatments highly triggered the growth of grasses followed by legumes and other species, with application of urea being the highest for all the plant compositions. This is because legumes respond less to N than grasses, grass dominant pastures will give greater responses to N (Steele 2008) the percentage increase in the proportion of grass reflects the role of nitrogen fertilizer in influencing the grass-legume botanical composition in favor of grass growth.

Result of the effect of years was significantly different for DMY while non-significant result was observed for the species composition. This could be attributed to the slow decomposition of slurry to be effective. It can also be explain that early application of slurry could also enhance the growth of all the plant species as effective as application of urea for later years.

Generally there was higher grass species composition across all the treatments including the urea applied plots. This result agree the reports on similar studies by Ashagre Abate (2008) who stated that in case of legumes, the average legume proportion was higher in the unfertilized plots (67.58%) than that in the fertilized plots which ranged from 50.97% to 27.63%. This may indicate that nitrogen fertilizer had an indirect suppressing effect on the proportion of legumes by inducing luxuriant growth and hence dominance of the grasses.

There was significantly higher difference for all the treatments compared across the years. It was also observed significant difference for DMY and legume species composition for all the treatments across the two years. Similarly, application of urea had highly significant difference for legume species composition across the two years. However, a non-significant result was found for grass species, legume and other plants species composition when compared across years for the rest of the treatments. Surprisingly, the control treatment and application of slurry had exactly similar results for DMY when compared across the two years. This means that application of slurry one year before has an advantage than enclosing only even if its rate of decomposition is slow.

Although, the biomass or DMY was significantly increased by application of slurry in the second year, the species composition for all the species remained exactly the same. From this it can be inferred that the difference in biomass yield was not due to the growth of new species but due to the effect of the slurry on the vigorousty in the second year of the existed species. However, the increase in DMY for the control plot was due to the increase in legume species composition and the increase in tillering capacity of the species, which could be as a result of prolonged effect of enclosure or exemption from intensive grazing. The higher and significant result of species other than grasses and legumes in both years could also be due to the presences of some undigested seeds from the manure used for the biogas production. Similar, result was forwarded by Ross (2005).

The highest results of grass species composition was observed in the urea applied plots. This is justified in Whiteman (1980) as application of nitrogen fertilizers to grass-legume pastures has dramatic effects on the legume component by altering botanical composition. Presence of high levels of nitrate or ammonium will inhibit nodulation and reduces rate of nitrogen fixation that leads to reduction in legume content. Similarly, Miles and Manson (2000) explained that when legumes are growing with grasses, the grasses are strong competitors for available nitrogen, and take up most of that applied. This will lead to an increased rate of growth, leaf expansion and tillering in the grasses, often leading to suppression of the legume owing to shading.

Cost benefit analysis

The cost was calculated based on cost needed for the different activities and in puts used for the application. However, the cost of harvesting and transporting ripe hay from pasture was not calculated. The price of one tone in the local area was $48.1. Although application of urea had higher biomass yield, it is not economical to use it for degraded range land rehabilitation as compared with application of slurry. This means that for every one $ addition cost of biomass yield production there is $ 8.73 and $ 0.864 return for slurry and urea, respectively. It is also environmentally friendly to use organic source of fertilizer than the inorganic one.

Conclusion

• For immediate soil fertility improvement application of inorganic fertilizer is important. However, for long term soil fertility improvement application of organic fertilizer such as slurry is an economical way of degraded pasture land improvement. Moreover, application of slurry and urea affected grass-legume species composition. It is highly recommended that for higher legume and grass species biomass yield application of slurry is appropriate.

Acknowledgement

We are greatly happy to thank Alamata Agricultural Research Center for financing the research work and the wereda, PA administrations and the farmers of the area for permitting the grazing land to undertake the research work. Heartfelt appreciation also goes to Dr, Yaynishet Tesfay for his support towards identification of the grass and legume species.

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Received 18 May 2015; Accepted 15 June 2015; Published 1 September 2015

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