Spatio-temporal variation of surface soil hydraulic properties under different tillage and maize-based crop sequences in a Mediterranean area

In arid and semi-arid regions, high intensity rainfall and/or irrigation water drop leads to development of surface crust, and it has the potential to alter surface soil hydraulic properties while also accelerating runoff and erosion. However, the temporal variation of soil hydraulic properties under irrigated conditions due to surface crust under different soil management practices has rarely been studied. On a long-term tillage field experiment (26 years), in Agramunt, NE Spain, a study was carried out using Beerkan infiltration tests in conjunction with the inverse optimization algorithms of  the BEST method (Beerkan Estimation of Soil Transfer parameters) to investigate the effects of surface crusting on the spatio-temporal variation of saturated soil hydraulic conductivity (K_s, mm s^-1), sorptivity (S, mm s^-0.5), mean pore size (r, mm) and number of hydraulically active pores per unit area (N, m^-2). Three tillage systems (intensive tillage, IT, reduced tillage, RT; and no-tillage, NT), two crop sequences (short fallow-maize, FM; and legume-maize, LM) and two positions (within the row of crops, W-row, and between the rows of crops, B-row) were assessed to evaluate the crusting effect on the above-mentioned soil hydro-physical properties. In response to autumn tillage, IT increased K_s and S due to higher r and N, but both declined after 60 days. RT, on the other hand, exhibited resilient to crust formation and despite having a lower N value, maintained comparable K_s and S values. After the spring tillage, its effect was immediately lost because of high-frequency water application, and both IT and RT developed crusted layers, resulting in decreased K_s, S and N. Long-term NT was resilient to form crust and an increasing trend of K_s and S was observed over time, except for the last sampling. Spatial variation (i.e., B-row vs. W-row) of K_s and S was found because of crusting, and independently of crop sequence, non-crusted soils (W-row) had consistently higher K_s (0.021 vs. 0.009 mm s^-1)and S (0.65 vs. 0.38 mm s^-0.5) than crusted soils (B-row) due to their lower bulk density and N. According to the findings of this study, conservation agriculture practices such as RT and NT improve the stability of surface soil structure and steadily reduce the risk of crust development. Further, surface cover by crops may help to prevent crust formation within the row of crops, improving soil hydraulic conductivity. This enhanced water flow path must not be neglected when measuring infiltration.