Influence of shade on mineral nutrient status of field‐grown cotton

Abstract

Photosynthetic irradiance has variable effects on cotton (Gossypium hirsutum L.) growth, development, lint yield and fiber quality. However, little is known about the effect of shade on the mineral nutrient status of cotton plants. A two‐year study was conducted to determine the effects of shade (63% light reduction) at different growth stages on mineral nutrient concentrations in plant components of field‐grown cotton. Averaged over the three growth stages of first flower, peak flower, and boll development, an 8‐day period of shade increased petiole NO₃‐N, phosphorus (P), potassium (K), and sulfur (S) concentrations by 145, 17, 20, and 18%, respectively. Total nitrogen (N), P, K, S, calcium (Ca), and magnesium (Mg) concentrations in the leaf blades of the sampled petioles increased 19, 29, 22, 22, 13, and 16%, respectively, compared with those of unshaded control plants. However, bracts and floral buds of 20‐day‐old squares of shaded cotton plants showed a slight decrease (6%) in total N concentration, and increases in the other mineral nutrient concentrations. The increased mineral nutrients of shaded plants were closely associated with decreased carbohydrate accumulation. Shade during plant reproductive growth significantly affected nutrient status and TNC/N ratio of cotton. This study indicated that light intensity at the time of sampling can cause non‐representative nutrient analysis and erroneous diagnostic recommendations. Therefore, the time of day and light conditions must be considered when sampling cotton petioles and other tissues for nutrient diagnoses.