Vertical Phosphorus and Potassium Stratification in No-Till Cotton Soils
- Donald D. Howard,
- Michael E. Essington and
- Donald D. Tyler
Continuous no-till production of cotton may result in vertical stratification of nutrients similar to that observed for band fertilizer applications. If so, special soil sampling techniques may be required to adequately address the fertility status of no-till soils. The objective of this study was to evaluate nutrient stratification relative to the planted row and with soil depth on three soils having broadcast K at various rates applied annually for 6 years to no-till cotton (Gossypium hirsutum L.). Rows were planted within a few centimeters of the rows from the previous year; a common practice in no-till agriculture. The selected soils were Memphis silt loam (fine-silty, mixed, active, thermic Typic Hapludalf), Lexington silt loam (fine-silty, mixed, thermic Ultic Hapludalf), and Loring silt loam (fine-silty, mixed, active, thermic Oxyaquic Fragiudalf). Potassium rates of 0, 28, 56, and 112 kg ha−1 were broadcast annually beginning in 1991. Experimental design was a split plot with five replications. Samples were collected from individual plots in the planted row (IR) and between the row (BR) to a depth of 30 cm. The soil samples were divided into 0- to 8-cm, 8- to 15-cm, and 15- to 30-em depths and Mehlich-1 P and K were evaluated. Mehlich-1 P varied with soil, sampling position, and soil depth. Differences in extractable P levels due to sampling position would not affect soil test ratings; however, additional years in no-till production may magnify position influences and so affect P fertilizer recommendations. Mehlich-1 K was greater for the IR sampling position of the 0- to 8-cm sampling depth for the three soils. Sampling only the BR position may in some instances give a lower soil test value, resulting in higher fertilizer applications. These differences varied with soil-applied K rates and may increase with additional time in no-till cotton.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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