STARTER FERTILIZER AND PLANTING DATE EFFECTS ON CORN ROTATED WITH COTTON

Corn (Zea mays L.) has become an important crop used in rotation with cotton (Gossypium hirsutum L.) in the mid-South region of the USA, but there has been little research on cultural practices for corn in this cropping system. The objective of this study was to determine if star ter fertilizer has beneficial effects on corn growth and grain yield a t different planting dates, Starter fertilizer and planting date effec ts were evaluated for corn in field experiments on a Commerce silt loa m (fine-silty, mixed, nonacid, thermic Aeric Fluvaquent) for 3 yr (199 1 through 1993). Six hybrids were evaluated with two starter fertilize r treatments at four planting dates. Starter treatments were (i) ammon ium polyphosphate (11-37-0 N-P-K) applied in-furrow and (ii) a control with no starter fertilizer. Planting dates were mid-March, early Apri l, mid-April and late April or early May, Yield response to planting d ate was not consistent across years; in two of three years, however, p lanting later than early April decreased yield. The starter fertilizer increased grain yield in two of the three years. Yield response to st arter fertilizer was not consistent across years, hybrids, or planting dates, The planting date x starter interaction for yield was signific ant in two of three years and the hybrid x starter interaction for yie ld was significant in one of three years. Starter fertilizer increased early-season plant height by 2 to 36% and increased grain yield acros s planting dates from 0.5 to 1.4 Mg ha(-1) in 1991 and 0.4 to 1.0 Mg h a(-1) in 1993. There was no yield response to starter in 1992. Applica tion of starter fertilizer, averaged across hybrids and years, reduced harvest grain moisture 5% and days to silking by 3 to 5 d, In this mi d-South study, in-furrow N-P starter fertilizer increased early-season corn plant height and grain yield and decreased the number of days to silking of corn rotated with cotton.