Effect of Rice Hull Mulch on Nutrient Concentration of Fertilized Irrigation Water

Parboiled rice hulls (PBH) have been shown to be an effective mulch for weed control in container crops. As with other mulch products, there is concern that PBH mulch would interfere with nutrient delivery to the crop. The objective of this research was to determine the effect of PBH mulch on nutrient concentration of fertilized irrigation water as it passes through the mulch layer, and the subsequent effect on growth and nutrition of container-grown sunflower (Helianthus annuus). Parboiled rice hull mulch was placed in Buchner funnels at a depth of 0, 0.63, 1.25, or 2.50 cm. Irrigation was applied with a water-soluble fertilizer (20N–4.4P–16.6K) injected at a concentration of 100 mg·L−1 N. Filtrates were collected after passing through the PBH in the Buchner funnels and analyzed for nutrient concentration. In a separate study, sunflower in no. 3 containers were mulched with the same depths of PBH and irrigated with water fertilized similar to that in the funnel experiment. Parboiled rice hull mulch caused a temporary and slight decrease in NO3− and NH4+ concentration. Phosphate and K+ concentrations generally increased with each irrigation event. Calcium and Mg exhibited an inverse relationship where the PBH mulch decreased Ca and increased Mg concentrations in the filtrates. Despite these measured differences in the chemical properties of water passing through the mulch layer, there were no measurable differences in sunflower growth or physical appearance, and only minor and inconsequential differences in plant nutrient status. Rice hull mulches are likely to have very minor effects on container crop nutrition with no adverse effect on plant growth over a 6 week production cycle as used in this experiment.