Abstract:
Agricultural practices of smallholders with low external and internal inputs fluxes cause the risk of depleting soil nutrient stocks, seriously threatening future agricultural production potentials in Ethiopia. To curb soil fertility depletion in these areas, it needs quantification of fluxes that are responsible for nutrient import into and export out of the farming system. The objective of this study was to quantify nutrient fluxes, pools and NPK balances at farm and field scales Yabala small village, Bedele District, South-western Oromia, Ethiopia. Through random sampling method three socio-economic groups (rich, medium and poor) were selected based on land holding size, number of livestock (oxen) and grain stocks. From a total of 42 household heads, 9 case study households were interviewed using NUTMON/MonQI structured questionnaire. Soil samples were collected from 0-30 cm depth and analyzed in each land units for both selective soil physical and chemical properties like soil texture, bulk density, pH, OM, total N, available P, exchangeable K and CEC. FYM, crop grains and crop residue samples were also collected and analyzed for their nutrient contents of total N, P and K. Four input fluxes, including inorganic fertilizer (IN1), manure (IN2), atmospheric deposition (IN3), and non-symbiotic fixation (IN4) and five output fluxes; harvested crop products (OUT1), crop residues (OUT2), leaching (OUT3), gaseous losses(OUT4) and erosion (OUT5) were quantified. The average farm management related nutrient balance from the study area was 11, -0.4 and -7 kg NPK ha-1yr-1 for rich,7, -0.1 and -5 kg NPK ha-1yr-1 for medium and 5, 1 and -3 kg NPK ha-1yr-1 for poor wealth groups respectively. An average full nutrient balance at farm scales were -10, -0.1, and -19kg NPK ha-1 yr-1 for rich, -11, 0.3 and -16 kg NPK ha-1 yr-1 for medium and -7,1.5 and -12 kg NPK ha-1 yr-1 for poor wealth groups respectively. Full nutrient flows showed that strong negative balances of N and K in all fields crops especially in sorghum field crop which revealed that -29 kg ha-1 yr-1 and -42 kg ha-1 yr-1 respectively. NPK nutrients mined were strong in higher endowed resource than less endowed resource; the output fluxes were higher than input fluxes. At farm scale full nutrient balance was recorded as -10 kg N ha-1 yr-1, 0.4 kg P ha-1 yr-1, and -16 kg K ha-1 yr-1. The highest depletion rate of PK nutrients in aggregated land units were recorded in LU4 which was (0.93 and 0.60% yr-1) respectively. An average depletion rate of NPK stocks were recorded as (-0.07, 0.08 and -0.31% yr-1) respectively in the study area. Therefore the study was clearly identifies the need for integrated soil fertility management to reverse the high rates of soil nutrient depletion in the study area. The possible measures can be suggested to use site specific and crop specific of blended fertilizer, organic matter, soil and water conservation technology and incorporation of crop residues based on field experimentations.