Vertical Phosphorus and Potassium Stratification in No‐Till Cotton Soils

Abstract

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‐cm 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.

Assessment of Soil Phosphorus and Potassium following Real Time Kinematic‐Guided Broadcast and Deep‐Band Placement in Strip‐Till and No‐Till

“…2C). Higher soil K test levels at IR than BR positions agree with fi ndings from others (Tyler and Howard, 1991;Howard et al, 1999;Varsa and Ebelhar, 2000). Mallarino and Borges (2006) also found that no-till systems at the 0-to 5-cm depth increment at IR had higher soil K test levels when K was broadcast-applied but they found no diff erences in chisel-disk or when no K was applied.…”

“…Th e increase in soil K levels at the surface was likely the combined effect of broadcast applications and crop cycling of K from the soil subsurface to the surface. Plant cycling of K at the IR position has been observed by others as well (Tyler and Howard, 1991;Howard et al, 1999;Varsa and Ebelhar, 2000). Th e diff erences described in the statistical analysis of main eff ects and interactions were more easily recognized and better explained in certain instances by measuring the change in soil P and K test levels resulting from the treatments over time.…”

“…A number of studies have shown the distribution of P and K levels in the soil aft er broadcast and banded fertilizer applications for no-till, ridge-till, chisel-plow, and chisel-disk (Kitchen et al, 1990;Tyler and Howard, 1991;Rehm et al, 1995;Howard et al, 1999;Varsa and Ebelhar, 2000;Mallarino, 2001, 2003;Rehm and Lamb, 2004;Mallarino and Borges, 2006;Farmaha et al, 2012). Relatively less is known about the distribution of soil P and K test level under strip-till.…”

Phosphorus fertilization, soil stratification, and potential water quality impacts

“…Early work on the impact of conservation tillage in agricultural soils led to the conclusion that P stratification may develop (Cruse et al 1983). No-till induced P stratification in cotton (Gossypium hirsutum) has resulted in a recommendation to update fertility recommendations for no-till soils (Howard et al 1999). Others have also concluded that in highly P stratified soils, P should be subsurface applied (Robbins and Voss 1991;Schwab et al 2006).…”

Conservation agriculture for small holder rainfed farming: Opportunities and constraints of new mechanized seeding systems

“…When topsoil dries, root access to the nutrients in the tilled zone diminishes. Minimum soil disturbance under CA generally results in stratification of nutrients with highest concentrations, particularly phosphorus (P) and potassium (K), either close to the surface or in planting rows (Howard et al, 1999). Minimum tillage increases fertilizer nitrogen (N) requirements at least in the initial years after transition to CA due to N immobilization by crop residues.…”