Poultry-Based Amendments and Cover Crop Residues Enhance Nutrient Cycling and Soil Health in Greenhouse Conditions

Abstract

Organic producers have few certified organic options to meet crop nitrogen (N) demand. Poultry-based amendments, including manures and processed fertilizers from livestock waste (e.g., feather meal), are commonly used in these systems, but synchronizing nutrient release with plant demand is challenging. Cover crop residues are also used in organic systems and interact with amendments to affect soil health and nutrient cycling. We conducted a greenhouse study to quantify the effects of four cover crop residues (millet, sorghum sudangrass, cowpea, sunn hemp) and three amendments (heat-treated poultry manure, poultry manure biochar, organic fertilizer) on spinach. We measured spinach yield and nutrient uptake; soil inorganic N; total soil carbon (C) and N; and two soil health indicators: permanganate oxidizable C (POXC) and autoclaved citrate-extractable (ACE) protein. Legume residues released the greatest inorganic N, whereas all cover crop residues exhibited a higher soil ACE protein concentration compared to the control without residues. The organic fertilizer released more inorganic N but had a lower ACE protein concentration than manure-based amendments. Grass residues increased POXC relative to sunn hemp, but cover crop residues had no effect on total C. In contrast, manure-based amendments increased soil’s total C but did not affect its POXC. Spinach yield and nutrient uptake were highest with biochar, with no consistent effect of cover crop residues observed on nutrient uptake. Overall, cover crops had the greatest effect on soil health indicators (POXC and ACE protein), whereas manure-based amendments had a greater impact on crop productivity and nutrition (spinach nutrient uptake and yield).