EFFECTS OF DIFFERENT SOURCES OF FERTILIZER APPLICATION ON SPECIES COMPOSITION, HERBAGE YIELD, NUTRITIONAL QUALITY AND SOIL FERTILITY OF DEGRADED GRAZING LANDS IN CENTRAL RIFT VALLEY OF ETHIOPIA

Abstract

The study was conducted in Arsi Negelle and Adami Tulu Jido Kombolcha (ATJK) districts from July to the end of September 2017, with the objectives to determine the effect of applying different sources of fertilizer on species composition, herbage yield and chemical composition of natural pastures and soil fertility status of pasture land. The experiment involved five treatments, i.e., (T1) control (no fertilizer application), (T2), a combination of urea and DAP (50 + 100 kg ha-1 respectively), (T3), cattle manure (7.5 t ha-1), (T4), wood ash (3 t ha-1) and (T5), lime (2 t ha-1). Soil samples were collected from 20cm depth before and after treatment were analyzed at Oromia Water Works Design and Supervision Enterprise. Forage samples were harvested from 50cm x 50cm at 50% of flowering stage were analyzed at ILRI analytic laboratory.. The soil textural and chemical properties of the study sites were significantly different (P<0.001). Soil textural classes were sandy loam in ATJK before and after treatment application and clay loam and silty clay loam in Arsi Negelle before and after fertilizer application, respectively. The pH values were significantly higher in the plots treated with wood ash; due to it attributed high composition of Ca and Mg. Total nitrogen and soil organic carbon content were significantly affected (P<0.001) by treatment application in ATJK. Twenty-four species were identified with 54.2%, 25%, 8.3%, 8.3% and 4.2% as different grass species, forb, legume, tree and sedge, respectively. In life form, 66.7% were annuals and the rest were perennials. More species composition and total DM yield were recorded in ATJK, due to decomposition and utilization rate of fertilizers is high at high temperatures. Chemical fertilizer and cattle manure application increased total biomass yield from 1.88 in control to 6.65 and 4.29 t ha-1, respectively. Grasses and legumes species composition were dominant in chemical fertilizer and cattle manure, respectively, while the control plot was dominated by forbs. The tallest mean plant height (72.6cm) was recorded in plots treated with chemical fertilizer, while the shortest (48.1cm) was observed under control plots at both study sites. Cattle manure application increased CP content of natural pasture from 9.58% in control to 15.74%, due to this treatment attributed the highest legume compositions. Wood ash application significantly improved ash content of pasture from 9.81% in control to 13.69%, which might be due to this content of high mineral recovery from the wood materials. IVDMD, ME, ADF and ADL of natural pastures were not affected by treatment application, however NDF was significantly affected (P<0.01). Chemical fertilizer application on degraded grazing land had economic value to invest more DM yield and brought more income from dry hay when sold at dry season as compared to the income obtained from the grain yield; on the other hand, net return of fresh hay from a fertilized plot by cattle manure was the best at harvesting time. In conclusion, chemical fertilizer is recommended for immediate soil fertility improvement, high DM yield production and achieves more income. However, for sustainable upgrading of degraded grazing land and quality forage production (high legumes botanical composition); cattle manure application is the right option for the local farmers.