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Fluid Journal : Fluid Journal 2002-2004
Early Spring 2004 Don't Overlook Effect of Variables on P Use in Corn-Soybean Rotations Dr Gyles Randall and Jeffrey Vetsch Summary: On low P-testing sites, starter fertilizer increased corn yield by 71 bu/A in 2002 and by 49 bu/A across the six years of the study. Soybean yields were increased by 18 bu/A in year 2002 and by 15 bu/A across five years of the study, due to the residual effects of the starter. Corn and soybean yields were generally increased over the 50- lb/A starter P and deep-band P treatments by the 100-lb/A broadcast P treatments, suggesting that band applications at a half rate are usually not sufficient in low to very low P-testing soils. On high P-testing sites, tillage did not affect corn yields in 2002 but did affect the six-year and five-year corn and soybean averages. Highest yields were generally found with the chisel plow system followed by one-pass and strip-till systems. Lowest yields were usually found with no tillage. Both corn and soybean yields were affected by the P treatments in 2002 because soil test P had declined to yield limiting levels in the control plots in the third year of the corn-soybean cycle. Economic return to fertilizer P averaged almost $100/A/yr on the low P- testing site with virtually no return to fertilizer P on the high P-testing site. On the low P-testing site, returns were greatest with the 100-lb/A broadcast treatment and lowest for the 50-lb/A "deep" band treatment. o-till corn production has provided serious challenges to corn growers in the northern portions of the Corn Belt, and has not been economically competitive with conventional-till systems. This is especially true on the highly productive Tillage systems, P placement, P levels in soils, and applied P rate can affect yields and economic return Minnesota studies show. Fluid Journal 1 N but poorly drained clay loam soils of northern Iowa and southern Minnesota where approximately 8 million acres are in corn production annually. Strip-till or zone-till is suggested as an alternative to no-till in these northern climates where soils are cold at the time of planting and are slow to warm. This fall tillage method disturbs the soil to a 7- to 8-inch depth and creates a 4- to 6- inch wide by 1- to 2-inch high mound of soil that is free of residue. Corn can be planted early and directly into the strip area that is warmer and drier. One-pass, secondary tillage systems consist of no fall primary tillage and either field cultivation or disking in the spring. This system is now quite popular for corn following soybeans in the Corn Belt. Use of conservation-till limits the opportunity for incorporation of P fertilizers that are broadcast. Optimum placement of P is therefore essential in reduced-till, especially in soils testing low in P. In this study, starter P was placed with the corn seed and the deep- banded P was placed 4 to 5 inches directly below the corn seed. Purposes of the portion of the study as reported here were to determine effect of P placement and rate on corn and soybean yield and economic return in one conventional-till and three reduced-till systems. Low P-testing Sites Corn yields in 2002 were excellent due primarily to above-average rainfall (May through September 20.2 inches), coupled with warmer-than-normal temperatures from June through September. Growing degree units for the growing season were 6 percent above normal. Under these favorable conditions, large yield responses to P were obtained on low P-testing soils with all four tillage systems (Table 1). Yields averaged 144, 164, 165, and 165 bu/A for the no-till, one-pass field cultivate, strip-till and chisel systems, respectively, when starter P was applied. The yield response to starter fertilizer averaged 71 bu/A across the four tillage systems with no tillage by starter fertilizer interaction. Corn yields were 15 to 32 bu/A greater for broadcast P (100 lbs/A of P2O5) compared to starter P (50 lbs/A of P2O5). Yields averaged 140, 153, 152, and 154 bu/A when starter P was applied for no- till, one-pass, strip-till and chisel + field cultivate systems, respectively, when averaged across the 6 years (1997 to 2002). A 49 bu/A yield response (101 vs 150 bu/A) was obtained with starter fertilizer when averaged across the tillage systems. No interaction existed between tillage and starter fertilizer. Corn yields with 100 lbs/A of P2O5 broadcast were 12 to 13 bu/A greater than with the 50-lb/A starter rate. These data suggest that band applications of P at a half rate on low to very low-testing soils are not sufficient to optimize corn yields compared to broadcast applications of P at a full rate.
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