Abstract
Soil erosion is a multifactor threat to crop production and the environment. Most studies on soil erosion characterization have not focused on soil nutrient loss associated with erosion. The aim of this study was therefore to quantify the magnitude of nutrient loss through soil erosion under different cropping systems and amendments to inform agronomic practices in sub-Saharan Africa (SSA). A field experiment was carried out on runoff plots with different cropping systems (sole maize, sole cowpea, sole maize and maize intercropped with soybean) as main plots and soil amendments (biochar, NPK (Nitrogen +Phosphorus +Potassium) fertilizer, NPK + biochar and a control (no amendment)) constituting the subplots in a randomized complete block design. For each block, a bare plot was included to assess the efficiency of the different crop and soil management practices on soil erosion. The study was carried out in three consecutive cropping seasons in the semi-deciduous forest zone of Ghana. The bare plots had the highest amounts of nitrogen (N), phosphorus (P), and potassium (K) eroded: 33.88, 12.35 and 12.75 kg ha-1 respectively followed by the control plots with magnitude of 20.43, 8.42 and 7.87 kg ha-1 respectively for N, P and K. Sole maize had the highest amounts of nutrient loss: 19.71, 8.12 and 7.27 for N, P and K respectively compared to all the other cropping systems where the losses varied respectively from 12.38 to 17.12, 6.67 to 7.49 and 5.81 to 6.75 kg ha-1 The legume-based cropping systems under inorganic fertilizer and biochar management effectively reduced nutrient loss more than all other treatment combinations. The off-site effect of soil erosion expressed as enrichment ratio (ER) was higher for all plots, which received inorganic fertilizer inputs varying from 1.93 to 3.06 while the other treatments had ERs of 1.51 to 2.03. The ERs of fine soil particles were greater than 1 (ranging from 1.14 to 3.6) being relatively higher than that of coarse particles (sand) with values below 1 (ranging from 0.62 to 0.88). The least cumulative monetary value of nutrient loss (30.82 US$ ha-1) was observed under cowpea cropping system which received NPK + BC treatment. Soil erosion affected directly soil nutrient depletion through nutrient loss; however, integrated soil fertility management associated with legume-based cropping systems can be alternative options to reducing its effects on croplands in SSA.
Highlights
Soil erosion reduces the agricultural value of lands via physico-chemical degradations
The highest nutrient loss was observed on the control plots and the least on plots, which received external inputs especially the inorganic fertilizer treatments associated with biochar
The bare plots, due to Treatments Cropping systems (CS) Cowpea (CW) Maize (MZ) Soybean (SB) Maize+Soybean (MZ+SB) CV (%) least significant difference (LSD) (5%) Soil Amendements (SA) Control Biochar (BC) Inorganic fertilizer (NPK) NPK+BC CV (%) LSD (5%) CS x SA MZ x Control MZ BC MZ x NPK MZ x NPK+BC M Z+SB x Control MZ+SB x BC M Z+SB x NPK MZ+SB x NPK+BC SB x control SB x BC SB x NPK SB x NPK+BC CW x Control CW x BC CW x NPK CW x NPK+BC CV (%) LSD (5%)
Summary
Soil erosion reduces the agricultural value of lands via physico-chemical degradations. Soil nutrient loss through runoff and sediment,is a major driver for soil fertility decline [1,2]. The eroded sediments or soil are highly concentrated with crop nutrients, which are washed away from farmlands. Erosion-based constraints coupled with unfavorable climatic conditions define significantly the productivity of farming systems in sub-Saharan Africa (SSA). Soil erosion leads to extreme losses of economic and environmental resources which negatively impact the economies of affected regions [3,4]. On-site consequences are directly observed on crop production as well as soil properties, affecting adversely the ability of the soil to respond to management practices with time. The amount of nutrients transported from croplands depends on the available soil management practices and the type of farming system
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