RESUMO
Soil fertility depletion is emerging as a serious challenge causing low crop yields and food insecurity in Ethiopia. An on-farm experiment was conducted in 2017/2018 cropping season to investigate the effects of combined application of compost and mineral fertilizer on selected soil properties and maize yield in North-western Ethiopia. Treatments were factorial combinations of three rates of Urea/NPSB (0/0, 50/50 and 100/100 kg ha-1) and three rates of compost (0, 5 and 10 t ha-1). The field experiment was arranged in randomized complete block design (RCBD) with three replications. Results showed that combined application of compost and mineral fertilizer significantly (p < 0.05) increased soil pH, organic carbon (OC), total nitrogen (TN), available phosphorus (AP), available sulphur (AS) and cation exchange capacity (CEC) compared to sole mineral fertilizer application and the control. On the other hand, there was significant (p < 0.01) decrease in soil bulk density. Plots amended with 10 t ha-1 compost and 100/100 kg ha-1 Urea/NPSB provided the highest maize dry biomass (18.62 t ha-1) and grain yield (6.07 t ha-1). Conversely, the lowest biomass (5.70 t ha-1) and grain (1.17 t ha-1) yields were obtained from the control. The partial budget analysis also showed that the highest net benefit (32700 Birr ha-1) was obtained from combined addition of organic and mineral fertilizer which was significantly higher than applying the highest rate of sole mineral fertilizer (27438 Birr ha-1), highest rate of sole compost (9011.3 Birr ha-1) and the control (7660 Birr ha-1). Therefore, we concluded that integrated fertilizer management improves soil properties and crop yield in the highlands of north-western Ethiopia.
RESUMO
Potassium (K) has been considered as a non-deficient nutrient in most Ethiopian soils. However, some studies recommended K application to K sufficient soils if K/Mg ratio is < 0.7. To resolve this controversy, field experiments and laboratory soil analysis were conducted in two districts (Yilmana Densa and Dera) in north-western Ethiopia on Mollic Nitisols (aric, humic) (pH = 5.5), Pellic Vertisols (aric, gilgaic, mazic) (pH = 6.2) and Vertic Luvisols (aric, nitic) (pH = 5.2) using wheat, tef and maize, respectively as test crops. The field experiments were laid out in a randomized complete block design with 7 K fertilizer rates (0, 42, 83, 125, 166, 208, and 249 kg ha-1 K) and four replications. KCl and DAP (200 kg ha-1) fertilizers were added at planting. Urea (200 kg ha-1) was added in split, half at planting and half at tillering for wheat and tef; and at knee-height stage for maize. Soil samples were taken two weeks after planting to determine K and Mg contents, K critical levels and optimum K/Mg ratio. The ammonium acetate extraction method was used to determine the K and Mg contents in the soil using a flame photometer and an atomic absorption spectrometer, respectively. Yield data were collected after harvest. The results of the study indicated that Mollic Nitisols (aric, humic), Pellic Vertisols (aric, gilgaic, mazic) and Vertic Luvisols (aric, nitic) had high K contents of 351, 380 and 434 mg kg-1, respectively. Rising K fertilizer levels increased soil K contents; however, this did not significantly increase crop yields. Mg contents were also in high category (>351 mg kg-1). The K/Mg values ranged from 0.60 to 0.80 in Mollic Nitisols (aric, humic), 0.70 to 0.88 in Pellic Vertisols (aric, gilgaic, mazic) and 0.71 to 1.04 in Vertic Luvisols (aric, nitic), and the values increased with an increasing K rates. However, wheat, tef and maize grain yields showed an increasing trend up to K/Mg ratio of 0.71 in Mollic Nitisols (aric, humic), 0.78 in Pellic Vertisols (aric, gilgaic, mazic) and 0.88 in Vertic Luvisols (aric, nitic), respectively, and declined above these values.
