Effects of long-term fertility management on the splash erodibility of ferruginous soils.

摘要

A splash-cup setup was designed, constructed and standardised using sand (500pm) and then used for the splash detachment tests. From plots under long-term fertility management for about 50 years, soil samples were collected and used for the study. Theplots had the following fertility treatments - fertilizer elements of dung or farmyard manure (D), nitrogen (N), phosphorus (P), and potassium (K) either singly or in combination (e.g. N, DNPK, DPK, NK, P, DNP, PK, DP, DNK, NP, DN, NPK and Control).Somephysical properties of the soil namely organic carbon content, pH, aggregate stability, bulk density, particle size composition and the consistency limits were determined. Raindrop sizes of 3.10mm, and 4.60mm were allowed to fall from a height of 7m onto the soil surface placed in splash cup setup to determine the splashing trends and resistance to splash erosion of the fertilizer-treated soils.The results showed that the undisturbed bulk density of the soil from plots treated with P and PK was highest(1650 kg/m3) followed by the Control (1620 kg/m3) and then NPK-treated plot (1610 kg/m3). Aggregate stability of 2.98 was highest for DNPK-treated soil followed by 2.64 for DNK, then 2.54 for the control and lowest was 1.35 for P-treated soil.Soil splash losses obtained from the study followed the trend of the equation established by (Obiechefu, 1985): S = bRA + a, where S = soil detached (g), RA = rainfall amount (ml), 'a' and 'b' are empirical coefficients.Projected field-scale of soil splash lossesobtained from the study ranged from 91 tonnes/ha for N-treated plot to 231 tonnes/ha for NPK-treated plot for the 3.10mm raindrop size, while for 4.60mm raindrop size the range was from 79 tonnes/ha for N-treated plot to 149 tonnes/ha for NK-treated plot.Combination of dung (D) and nitrogen (N) was found to increase resistance of soil to erosion (reduced erodibility) whereas potash (K) and phosphorus (P) either singly or in combination with the other fertilizer elements caused soil to be more susceptible to splash erosion (increased erodibility). Dung and Nitrogenous (N-treated soils) fertilizers reduced soil splash loss, while phosphoric and potassic fertilizers increased soil splash loss. Combination of N, P and K or NPK treated soil increased splasherodibility of the soil.This study shows that long-term fertility management was found to affect the splashing characteristics and the erodibility of soils. It also shows that long-term fertility managementhad significant impact on some surface soil physical and chemical properties and that fertility treatment of land must therefore, be carefully managed to prevent soil erosion and for sustainable land use and crop production.