Single biochar application enhanced the effectiveness of organic fertilizers in a continuously cropped soil

Abstract

Indiscriminate use of chemical fertilizers has profound environmental implications that organic fertility options can circumvent. Lower macronutrient contents that warrant higher tonnage application rates hinders achieving higher relative agronomic efficiencies (RAE) in these organic fertilizers. The effects of short-term usage of organic fertilizers on selected soil and plant parameters and the potential of harnessing biochar’s unique characteristics to improve RAE of other organic fertilizers at reduced application rates were evaluated. The seven-year (2015 to 2021) field trial composed of two near raw organic fertilizers: Gliricidia sepium leaves (GL) and poultry manure (PM) and two composted organic materials: sole compost (SC) and bone meal fortified SC termed phosphocompost (PC). There were also two control treatments: chemical fertilizer (sole CF) and absolute control (AC). Each organic fertilizer was applied at 5 t ha-1 during 2015 to 2019 cropping seasons. In 2021, biochar was coapplied at 0.5 t ha-1 with the other organic fertilizer at a reduced rate of 2.5 t ha-1. Data taken on soil organic carbon (SOC), available P, dry grain (DGY) shoot weights (DSW), and grain N and P contents at the end of the 2015, 2019, and 2021 cropping seasons were subjected to analysis of variance. Treatment means of the selected years were compared using Chi-square at P<0.01, followed by computation of the RAE of each organic fertilizer with and without biochar application. Sole CF reduced SOC and DSW of maize by 145.8 and 3.2%, respectively. Sole near raw organic fertilizers reduced SOC by 18.8% (GL) and 19.2% (PM), while SC increased it by 16.4%. One-time biochar spiking at reduced organic fertilizer rate increased SOC, available P, grain yield, P, and N contents. The RAE of the near to raw organic fertilizers were more responsive to biochar in enhancing SOC and grain P contents while biochar favored composted organic fertilizers for enhanced soil available P, grain, and shoot weights.