Soybean Yield Response to Various Depths of Erosion on a Fragipan Soil
Erosion of soils with limited profile thickness can reduce soil productivity to the point that crop yields are no longer profitable. The intention of this study was to determine the effects of progressive erosion on the productivity of a fragipan soil. Soybean [Glycine max (L.) Merr.] was the indicator crop. Twelve experimental plots were installed at each of the three differentially eroded sites on a Grenada silt loam (fine silty, mixed, thermic Glossic Fragiudalf). Average depth to fragipan ranged from 16 to 63 cm. Soil P and K levels were adjusted to 140 and 280 kg ha−1, respectively, on one-half of the plots, and pH was adjusted up to 6.5. The remaining plots received no lime or fertilizer. No significant differences were found for yield between the two fertility treatments. Average grain yields for the 3-yr study were 2417, 1953, and 1877 kg ha−1 at the slight, moderate, and severely eroded sites, respectively. The lowest yields, for these same plots were 2286, 1773, and 1549 kg ha−1 recorded in 1986, when soil water content during pod-fill stage was least. Depth to fragipan accounted for 56, 60, and 67% of the variability in grain yields for 1984, 1985, and 1986, respectively. A yield-depth-to-fragipan curve derived from these data showed that the greatest grain-yield reduction per increment of soil loss occurred as soil depth decreased from 60- to 50-cm. This indicates that, to maintain productivity on these soils, management systems should be designed to preserve a minimum soil thickness above the fragipan of ∼60 cm.
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