Effect of Biochar on Soil Physical Properties, Water Use Efficiency, and Growth of Maize in a Sandy Loam Soil

Abstract

There has been claims that biochar improves water retention in soil and aid in improved crop productivity. Hence, recent conservation practices in the area of agricultural lands have focused research attention on the performance mechanism of biochar. In this study, the effect of corn cob biochar particle sizes (<2 mm & ~2-4 mm) and amounts (0, 20, 40, 80 tons/ha) on soil physical properties (soil bulk density and soil water retention) and biomass yield were investigated. It further investigated the effect of deficit (DI) and full (FI) irrigation in combination with biochar on plant physiology and water use efficiency. Corn cob biochar was mixed with the top 20 cm sandy loam soil at a rate of (0, 20, 40 & 80 tons/ha) in pots made of PVC columns (20 cm diameter x 75 cm height). Three maize seeds were planted and thinned out two weeks after planting leaving one maize plant per pot. NPK fertilizer (3.1 g) was applied to all pots. Soil moisture content reading was taken every third day for the first three weeks and every second day afterwards. From the beginning, each pot was supplied with the amount of water lost to restore to field capacity. After three weeks, deficit irrigation (DI) strategy was implement. All full irrigation (FI) treatments were irrigated immediately water loss exceeded a management allowable depletion (MAD) of 30 % of the pot field capacity, and for the DI treatments at MAD of 80 %. Three drying cycles were achieved between day 26 and day 70 (last day of terminating the work). The results showed that bulk density (BD) decreased significantly between the control (1.46 g/cm3) and the 80 tons/ha (1.30 g/cm3) biochar treatment. Also, BD decreased insignificantly with decreasing biochar particle sizes relative to the control. BD was found to decrease with increasing biochar fine i.e. (CBP (2- 4 mm)> FBP (<2 mm)). Bulk densities of 1.39 g/cm3 and 1.35 g/cm3 were found for the coarse biochar particle (CBP) and fine biochar particle (FBP) respectively relative to the control 1.46 g/cm3. Soil water retention characteristics were affected by addition of biochar. The result shows that addition of 20 tons/ha biochar surprisingly did not alter the curve that much though at higher matric potential tends to hold substantial amount of water relative to the no biochar treatment. However, biochar application rate of 80 tons/ha had significant effect relative to the control. It was discovered in general that, applying corn stover biochar at a rate beyond 20 tons/ha will improve the water retention characteristic of sandy loam soil. Furthermore, biochar particle size also affected the water retention characteristics as it was discovered that, the FBP retained more water at low matric potential but as matric potential increased beyond -300 kPa, the CBP retained more water. Furthermore, the biomass yield (BY) results showed a yield loss of 21.2% for DI treatments relative to the FI treatments. However, 59.2% water was conserved in this case for the DI treatments. This implies biochar addition to soil with deficit irrigation practices may be a promising water conservation strategy. It was also observed that, the yield values for the DI biochar treatments were close to the FI control values. Transpiration efficiency was significant between the DI treatments (32 g/mm) and the FI treatments (20 g/mm). Plant physiology was also enhanced by the addition of biochar even though the differences were not consistently significant. Therefore, it is concluded in this study that addition of corn cob biochar does improve soil physical properties and enhance water retention within the soil, and that biochar amendment in combination with deficit irrigation does have the potential to improve water use efficiency by enhancing plant physiology and yield.