Response of corn and cotton to starter phosphorus on soils testing very high in phosphorus
Phosphorus from agricultural lands poses a problem in water resources. In 2003, more than 48% of soil samples submitted to the North Carolina Department of Agriculture and Consumer Services (NCDA&CS) soil testing laboratory tested very high in soil P (>120 mg dm–3 P). As soil test P increases, off-site P loss increases, through erosion, soluble P runoff, or leaching. On soils testing above high soil test P (60–120 mg dm–3 P), studies from the northeast and midwest United States demonstrate that no corn (Zea mays L.) or cotton (Gossypium spp.) yield response from additional fertilizer is expected. However, there have been limited studies on the effects of starter-P fertilizer on soils with very high P status in North Carolina and the southeast. Therefore, we undertook a study in the three physiographic regions (coastal plain, piedmont, and mountains) of North Carolina to determine if the use of starter-P fertilizer would affect the growth of corn and cotton on soils having very high soil test P. Treatments were starter N and P, and starter N only. Treatment differences were not observed for corn, while the N-only treatment had greater tissue N than the N- and P-starter treatment in Piedmont cotton. Additionally, the use of only starter-N is typically more cost effective than using both N and P starter fertilizer. For production, environmental, and economic reasons, starter-P fertilizer is not warranted on North Carolina fields with very high soil test P values.