Seasonal changes in soil physical properties under long-term no-tillage

There is no consensus regarding seasonal changes in soil physical properties within and between rows in long-term no-till (NT) crop production systems. We hypothesized that soil physical properties in a Rhodic Ferralsol under long-term NT differed within and between rows and that these changes are influenced by wetting and drying cycles (WDC). Undisturbed samples were taken within and between crop rows from layers of 0 to 0.10 and 0.10 to 0.20 m depth in September 2010, 2011 and 2012 and March 2012 and 2013. At the first sampling, 40 soil samples were collected within the maize (Zea mays L.) row (R), at interrow (IR) sampling positions, and at an intermediate position (IP) between R and IR. Coordinates for each sampling point were identified so that subsequent samples could be collected from the same location. Soil bulk density (Db), soil water retention curve (WRC), S index, air-entry pressure and pore size distribution were determined. The results confirmed that furrow opening causes significant positive changes in soil physical properties within the crop row and plant growth can be affected by the "confinement" of roots within the R position within long-term NT sites. With each successive sampling, Db decreased and was significantly influenced by recent WDC. The pore size distribution showed larger pores with each successive sampling, providing a higher S index, air-entry pressure, and improved soil physical quality over time. The steady state of soil structural conditions achieved at long term NT can be affected by short term influences related to the crops and weather conditions. However, soil physical properties indicated that a new equilibrium was achieved and that soil under long-term NT may remain physically functional. Our results confirm that soil physical properties under NT are highly dynamic and strongly influenced by (i) soil disturbance caused by furrow opening, (ii) wetting and drying cycles, and (iii) sampling depth. Therefore, we recommend that for quantifying soil physical quality within no-till fields, measurements should be taken within and between crop rows..