Effect of Rotational Crop Residues On Chile (Capsicum annuum) Germination and Vigor

Allelopathy is the chemical inhibition of one plant, or organism, by another plant due to the release of chemicals into the environment that act as germination or growth inhibitors. The compounds left behind by one crop plant (often grains) can affect the growth of subsequent crop plants. Ninety-seven percent of the producers in southern New Mexico reported they plant chile peppers in rotation with other crops, including small grains. However, the effect of rotational crops on chile pepper performance and yields has not been explored.  In 2008-2010, residues of twelve common rotational crops were collected from agricultural fields. These residues included chile (roots and stems), wheat (stubble and roots), cabbage (roots and leaves), broccoli (roots, leaves, and stems), cotton (roots, stems, and fibers), sorghum (stubble, and roots), onion (skins, leaves, and roots), alfalfa (stubble and roots), and rye (stubble and roots). Allelopathic substances were extracted in cold water, lyophilized, and stored at -80°C until use. For each experiment, lyophilized crop residues were rehydrated, filter sterilized, and evaluated in the laboratory. Surface sterilized chile (‘NuMex 6-4’) seed and lettuce (‘Black Seeded Simpson’) were the crop plants of interest. The experiment was arranged in a Completely Randomized Design (CRD) that consisted of 15 seeds of species per Petri plate with five plates per treatment, and three replications. The entire experiment was conducted twice. Treatments included lettuce as an indicator crop due to sensitivity to allelopathic compounds, a deionized (DI) water control, a low concentration (50 mg dried residue, powder dissolved in 198ml of DI water), and high concentration (100mg in 198 ml of DI water). Lettuce was incubated in the dark at 22°C and evaluated after three days. Chile seeds were incubated under fluorescent lights for ten days. Both crops were evaluated for vigor (radicle length) and percent germination, normalized to the control, and analyzed statistically. Lettuce and chile showed different sensitivities to the same residue. Sorghum residue at the lowest concentration caused a complete inhibition of both germination and radical elongation in chile. In contrast, oats reduced chile germination by 37% and 87% in the low and high residue concentrations, respectively. In addition, radicle length was reduced by 38% and 79% for low and high residue concentrations, respectively. These laboratory results provide evidence that rotational crops affect subsequent vegetable growth, and may affect cropping system choices.