Pyroligneous Acid Enhances Mung Bean Yield 34% in Sodic Soil
Introduction
Mung bean (Vigna radiata) is a widely cultivated pulse crop valued for its high protein content (about 24.3%), essential amino acids, and ability to enrich soil fertility through nitrogen fixation. However, large tracts of arable land are compromised by sodicity, where elevated soil pH, excess sodium (Na), and degraded soil structure severely limit crop growth. Sodic conditions often reduce water infiltration and nutrient availability, resulting in lower yields.
Pyroligneous acid (PA), commonly referred to as wood vinegar, is a byproduct of the pyrolysis (carbonization) of wood or biomass. It is a complex mixture of organic acids, phenols, and other compounds, with a naturally acidic pH (2–4). Previous studies have indicated that PA can enhance germination, promote microbial activity, stimulate plant growth, and improve nutrient availability in soil. Given these promising properties, researchers set out to evaluate whether PA could help reclaim sodic soils for mung bean cultivation. The study summarized here explored PA seed priming, its addition to gypsum (a sodic-soil amendment), and foliar spraying of PA at critical crop stages.
Experimental Design and Application
A field experiment was conducted during the summer season at Anbil Dharmalingam Agricultural College and Research Institute in Tiruchirappalli, India, where soil pH registered at 8.9—falling under sodic conditions. The researchers tested ten treatments in a randomized block design, each replicated three times. Key components and treatments included:
- Seed Priming: Some plots used mung bean seeds primed with PA at a 1:500 dilution (1 mL PA in 500 mL water) prior to sowing. Others used unprimed seeds to compare the effect of PA on early seedling vigor.
- Gypsum Application: Gypsum was applied at 50% of the gypsum requirement (GR) needed to partially reclaim the sodic soil (3.2 t/ha). In selected treatments, this gypsum was pretreated with PA in two ratios (1:5 and 1:10), left to react for 15 days, and then incorporated.
- Foliar Spray of PA: Two foliar spray concentrations (1:300 and 1:400) were applied at 30 and 45 days after sowing (DAS), targeting flowering and pod formation stages. The recommended dose of N, P, K (25:50:25 kg/ha) was uniformly given in all but the absolute control treatments.
Experimental plots (5 m × 4 m) were carefully leveled to maintain uniform irrigation. Standard agronomic practices were followed, and plant measurements were recorded from germination through harvest.
Table: Overview of the Ten Treatments
| Treatment | Description |
|---|---|
| T1 | Absolute control with unprimed seeds (no PA, no gypsum, no foliar PA) |
| T2 | Absolute control with PA-primed seeds (1:500), no gypsum, no foliar PA |
| T3 | Unprimed seeds + 50% GR alone |
| T4 | PA-primed seeds (1:500) + 50% GR alone |
| T5 | PA-primed seeds (1:500) + 50% GR treated with PA (1:5) |
| T6 | PA-primed seeds (1:500) + 50% GR treated with PA (1:10) |
| T7 | T5 + foliar spray with PA (1:300) at 30 and 45 DAS |
| T8 | T6 + foliar spray with PA (1:300) at 30 and 45 DAS |
| T9 | T5 + foliar spray with PA (1:400) at 30 and 45 DAS |
| T10 | T6 + foliar spray with PA (1:400) at 30 and 45 DAS |
Key Findings
1. Growth Parameters
- Plant Height and Leaf Area Index (LAI): The tallest plants (50.4 cm) and highest LAI (3.91) were noted in T10 (PA seed priming, PA-treated gypsum at 1:10, and foliar PA at 1:400).
- Dry Matter Production (DMP): T10 recorded 2576 kg/ha, reflecting robust vegetative growth. Even a modest foliar PA spray contributed to higher leaf biomass.
2. Yield Attributes
- Pods per Plant and Seeds per Pod: T10 achieved 38.4 pods per plant and 12 seeds per pod, clearly surpassing the control.
- Grain Yield: T10 outperformed all others with 749 kg/ha. The next-highest yield (698 kg/ha) was from T8 (PA priming, gypsum + PA (1:10), foliar PA at 1:300). Notably, T10’s yield was 34% higher than the simpler 50% GR-only approach.
- Haulm Yield: Similar trends appeared in haulm yield, highlighting PA’s broad contribution to plant vigor.
3. Mechanisms and Observations
- Pyroligneous acid’s organic acids (acetic, formic), phenols, and esters seem to boost chlorophyll and photosynthesis.
- Its acidification effect enhances gypsum solubility and nutrient release, improving root uptake.
- Higher microbial activity in PA-treated soils accelerates nutrient cycling and plant growth.
Implications
- Seed Priming Advantage: PA-primed seeds showed faster germination and better early vigor, even in highly alkaline conditions.
- Improved Nutrient Use: Treating gypsum with PA increased solubility of calcium, displacing sodium from exchange sites.
- Higher Yield and Sustainability: Combining partial soil reclamation (gypsum) and foliar PA sprays drove yield improvements and supported gradual sodic soil improvement.
- Practical Rates and Timing: Foliar spraying PA twice (30 and 45 DAS) at 1:400 or 1:300 delivered the best results under sodic conditions.
Overall, this study shows that pyroligneous acid is a versatile tool for enhancing pulse production in saline or sodic environments, where poor soil structure and high pH often restrict plant performance.