Soil Type and Wetness Affect Tint of Peanut ( Arachis hypogaea L.) Pod Shell

Abstract

Peanut (Arachis hypogaea L.) is a globally important legume crop that is utilized fresh, roasted, or pressed for oil products. A substantial market exists for in-shell peanuts, and shell color is an important factor affecting price — consumers favor bright yellow. Field observations have indicated that the type of soil in which the peanut pods develop can affect shell color and tint. Field and greenhouse experiments in which plants were grown in sandy soil while pods were allowed to develop in various tested soils verified this primary observation: sandy soils resulted in bright-yellow shells, dark soils (such as peat) resulted in a darker shell color, while loess soils resulted in intermediate shell colors. Incubation of peanut pods in saturated soil solutions or filtered soil extracts inferred the existence of two opposing processes that may affect shell color: adherence of water-soluble soil components to the shell surface, and the washing-off of shell material from this surface. Overhead irrigation with a reduced amount of water or watering with a subsurface drip system concealed at a depth of 25 cm resulted in brighter shell colors than applying the normal amount of water by overhead irrigation. These data suggest that reducing soil wetness in the pod-development zone may increase shell brightness. Field experiments also indicating that final shell color is determined towards the end of pod development, suggesting that soil wetness in the pod-development zone should be controlled during at least the last 4 weeks of growth, to maintain a low level of wetness.