Reduction of compost phytotoxicity during the process of decomposition

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• Hog manure composting is crucial for waste management and nutrient recycling.
• Phytotoxicity in composted manure can inhibit plant growth.
• Understanding factors influencing phytotoxicity is essential for producing safe soil amendments.

Purpose of the Study:

• To assess the phytotoxicity of composted hog manure under different operational strategies.
• To correlate phytotoxicity with chemical properties of the manure.
• To identify optimal composting conditions for eliminating phytotoxicity.

Main Methods:

• Bioassay using cress (Lepidum sativum L.) to measure seed germination and root growth.
• Analysis of water extracts for chemical properties (electrical conductivity, nitrogen, C:N ratio, heavy metals, humification).
• Multiple regression analysis to determine key factors affecting phytotoxicity.

Main Results:

• Germination Index (GI) negatively correlated with extractable copper (Cu), zinc (Zn), and ammonium nitrogen (NH(4)(+)N).
• Phytotoxicity disappeared (GI>80) when NH(4)(+)-N, Cu, and Zn concentrations reached specific thresholds.
• Ammonium nitrogen (NH(4)(+)-N) was identified as the primary factor influencing phytotoxicity.

Conclusions:

• Composting strategies significantly impact the rate of composting, maturation, and phytotoxicity reduction.
• Phytotoxicity disappearance aligns with manure maturation.
• Optimal conditions (e.g., turning every 4 days, 60% moisture) can eliminate phytotoxicity within 56 days.