SOIL Phosphorus Distribution.

Understanding how the spatial distribution of phosphorus (P) relates to sowing lines and soil depth is essential for improving fertilization practices for no till (NT) management systems. The objectives of this study were (i) to characterise the spatial micro-variability of soil P in both NT and mouldboard plough (MP) using 2D geostatistics analyses (semivariograms), (ii) to describe the pattern of soil P distribution at either side of the seeding row in both NT and MP management systems, and (iii) to determine the appropriate area and depth to sampling soil in a field under NT conservation practices compare to the MP management system. Six experimental units (the two tillage practices i.e., MP and NT and 3 blocks) were implemented with a nested grid sampling. The principal grid (2.5 m x 0.38 m distance between each 35 sampling points) consisted of 7 transects (perpendicular to row direction) and five transects (located on 3 interrows and 2 rows corn i.e. 3^rd and 4^th rows plot). Three of the seven transects had more intensive interrow sampling points (distance between the sampling point 0.076 m perpendicular to the row; 16 additional sampling points per transect). A total of 996 soil samples (= 83 per depth and experimental unit x 2 depths and 6 experimental units) were collected for the spatial micro-variability study. Weak spatial structures were evident from the semivariogram parameters, indicating a predominance of random factors on the measured Mehlich-3 P. Similar sampling strategy design would therefore be suitable for the two tillage management systems in this long term corn-soybean rotation.