Abstract
Core Ideas 2‐D distribution of Mehlich‐3 P across seeding row had no spatial pattern in no‐till and moldboard plow. Horizontal distribution of Mehlich‐3 P was less sensitive to extrinsic factors. Soil‐surface P accumulation in no‐till is due in part to P recycled by corn and soybean. Surface P accumulation in no‐till is also due to the replenishment of solution P by residual P. Improving soil test P assessment at plot scale is essential for productivity in conservation agriculture systems. We characterized the distribution of Mehlich‐3 P (PM3) concentrations at the decimetric scale with depth on either side of the sowing row in no‐till (NT) and moldboard plow (MP) plots fertilized with 35 kg P ha–1 every 2‐yr in a corn–soybean rotation (20‐yr). A total of 996 soil samples (83 samples × 2 depths [0–5 and 5–20 cm] × 6 plots [3 blocks each MP and NT]) were collected at corn harvest in 2012. The average PM3 concentrations in the 0‐ to 5‐cm layer were 35.7 and 63.4 mg kg–1 in MP and NT, respectively. The PM3 concentration in the 5‐ to 20‐cm depth was similar between MP and NT and averaged 32.0 mg kg–1. The horizontal distribution of PM3 concentrations in these plots was less sensitive to extrinsic factors including tillage, P fertilization and soil depth. High coefficients of variation were associated with PM3 data in both MP (77 and 63% at 0–5 and 5–20 cm, respectively) and NT plots (46 and 66% at 0–5 and 5–20 cm, respectively). It is possible that this strong overall variability overshadowed any PM3 pattern that could have been introduced by NT management. Geostatistical semivariance analysis indicated a predominance of random spatial dependence in most plots, except two plots (one MP and one NT) with moderate spatial structures. The 2‐D geospatial model related to tillage was not detected by the sampling grid used at this experimental site. Therefore, a similar sampling strategy would be appropriate and could be recommended for these two tillage systems in this long‐term corn–soybean rotation.
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