Wood Vinegar Improves Cowpea Yields By Up To 66%
Introduction
In an era where sustainable agricultural practices are becoming increasingly important, researchers are exploring alternatives to synthetic fertilizers that can enhance crop productivity without harming the environment. Wood vinegar, a byproduct obtained from the pyrolysis of plant biomass during biochar production, has emerged as a promising solution. A recent two-year field study conducted by researchers from Ghana's Council for Scientific and Industrial Research (CSIR) and Prairie View A&M University has revealed significant benefits of wood vinegar application on cowpea production and soil health.
Wood vinegar, also known as pyroligneous acid, contains over 200 water-soluble chemical compounds, including organic acids, alkanes, phenolic compounds, alcohol, and esters. As a natural biostimulant and biopesticide, it offers multiple agricultural benefits while posing minimal environmental risks, making it an ideal candidate for sustainable farming systems.
Experimental Design and Application
The researchers conducted a field study in Nyankpala, Ghana, to determine the most effective method of applying wood vinegar for enhanced cowpea production and soil health. The experiment used a randomized complete block design with four replications, comparing three application methods: a control (no wood vinegar), soil drenching, and foliar application.
Commercial wood vinegar branded as "organic farming aid" (OFA) was diluted to a 0.2% concentration (1:500) and applied at a rate of 300 mL/ha. For the soil drenching method, the solution was applied directly to the soil surface near the rooting zone using a knapsack sprayer, while foliar application involved spraying directly onto the leaves. Applications began at 25 days after planting (V4 stage) and continued weekly, with sampling conducted every 14 days to assess various plant and soil parameters.
Key Findings
Enhanced Crop Performance
Both application methods significantly improved cowpea growth and yield compared to the control. Soil drenching produced the most outstanding grain yield, increasing it by 45.5% and 66.3% over the control in 2021 and 2022, respectively. Foliar application increased grain yield by 28.3% and 30% during the same periods.
While soil drenching excelled in grain production, foliar application showed superior results for biomass (stover) yield at harvest. This suggests that foliar application might be particularly beneficial in agropastoral farming systems where crop residues are used as livestock fodder.
The study also found improved nodulation in plants treated with wood vinegar, with soil drenching and foliar application increasing nodule mass by 18.3% and 14.2%, respectively, compared to the control. This enhanced nodulation likely contributed to better nitrogen fixation, a crucial process for leguminous crops like cowpea.
Improved Soil Health
Wood vinegar application significantly enhanced soil biological and biochemical properties. Soil enzymes including α-glucosidase, acid phosphatase, dehydrogenase, and arylsulphatase showed increased activity in treated plots, with average improvements of over 60% compared to the control.
Soil drenching particularly improved permanganate-oxidizable carbon (POXC) and microbial biomass nitrogen (MBN), indicating enhanced soil carbon sequestration and nitrogen cycling. These improvements in soil health indicators correlated strongly with the observed increases in cowpea productivity.
Economic Benefits
The economic analysis revealed that both application methods were financially viable, with value-cost ratios (VCR) exceeding 1.0. Soil drenching yielded the highest average return on investment (VCR = 2.24), followed by foliar application (VCR = 1.77), compared to the control (VCR = 1.27). This indicates that for every dollar invested in wood vinegar technology, farmers could expect returns of $2.24 or $1.77 for soil drenching and foliar application, respectively.
Implications
This research demonstrates that wood vinegar application, particularly through soil drenching, offers a sustainable approach to enhancing cowpea productivity while improving soil health. The dual benefits of increased crop yields and enhanced soil quality make wood vinegar a promising technology for smallholder farming systems in Ghana and potentially other sub-Saharan African countries.
For farmers practicing agropastoral systems, the choice between soil drenching and foliar application might depend on whether their primary goal is maximizing grain yield or biomass production. However, both methods provide significant improvements over conventional practices and represent economically viable options for sustainable intensification of cowpea production.