Do agriculture management operations and their seasonal dynamics affect soil hydraulic properties?

In agriculture, soil management practices directly affect soil structure and herewith soil hydraulic properties (SHP), namely the water retention curve (WRC) and the hydraulic conductivity curve (HCC). Although it has been hypothesized that management practices affect the wet range of both the WRC and HCC, limited experimental data exists on the topic. Currently, the full extent of these effects is not well understood and is often overlooked in soil-plant-atmosphere models. This study aims to characterize the WRC and HCC, from saturation to oven dryness, for one soil subjected to common agricultural practices for over 30 years.  

During one growing season, 160 undisturbed soil cores were collected at three different times (mid- season, post-harvest, and after seedbed preparation) from the topsoil (5–10 cm depth) and subsoil (30–35 cm depth) in a long-term field experiment. This experiment included plots managed with conventional plowing, two types of mulching, and direct seeding, all with the same loamy soil texture and crop rotation. To quantify SHP,  four laboratory methods were employed for the same soil core: the Falling Head method for saturated hydraulic conductivity (Ksat), the Multistep Flux method for estimating near-saturation conductivity to capture the structural effect on the HCC, the evaporation method for the wet and mid-range of WRC and HCC (pf < 3), and the dewpoint method for the dry part of the WRC.  

The results show that 30 years soil management practices directly affect the SHPs of the topsoil and not of the subsoil, with the highest changes at the wet range (pF < 1) of the WRC. Conventional plowing resulted in 8% higher water content at pF<1 compared to direct seeding, while both mulching treatments were closer to the direct seeding. In the dry range of the WRC, no differences were observed between the management practices, supporting the assumption that this range is controlled by soil texture.  For the HCC, we measured on average a 35% higher ksat for conventional plowing compared to cores taken under direct seeding. It is noted that ksat measurements of all treatments showed high variability. For the near saturation conductivity, we observed a highly bimodal behavior for all treatments. We conclude that the structural effect of agriculture managements operations controls the wet range of both the WRC and HCC and soil texture controls the dry range.  Seasonal dynamics were observed in all topsoil treatments and current results indicate that the wet part of the SHP varies during a single season, with the most changes occurring between post-harvest and seedbed preparation. Overall, this study presents experimental evidence on the effect of soil structure on SHP and its potential effect on soil water dynamics.