Water dynamics of cover crops: No evidence for relevant water input through occult precipitation

Abstract

Rising temperatures and disruption of rainfall patterns due to climate change make water a limiting growth factor even in regions of temperate climates. Thus, producing 'more crop per drop' is of utmost importance. While cover crops provide many benefits to cropping systems, their influence on soil water is discussed controversially. While an increase in transpiration can lead to soil water depletion, the reduction of evaporation in combination with possible additional water inputs could provide a water benefit for a succeeding crop. Occult precipitation could be such an additional water input. The objective of this study was to quantify whether cover crops provide a net water benefit over a bare fallow due to the occurrence of occult precipitation. In a 2-year experiment, seven different cover crops were cultivated in pure stands and as a mixture under semi-controlled conditions in a container experiment. Water fluxes and meteorological conditions were closely monitored. Although favourable conditions occurred during both vegetation periods, we found no evidence of occult precipitation. In autumn, soil water was depleted by fast-growing cover crops. In winter, soil water was recharged due to the early preparation of a mulch layer combined with high winter precipitation while in early spring rising temperatures increased transpiration losses of a winter-hardy cover crop, leading to a reduction of soil water. For middle European conditions, this shows that (1) living cover crops do not provide any water benefits and that (2) soil water recharge in winter is highly dependent on meteorological conditions and cover crop management. From a water budget viewpoint, negative effects on a succeeding cash crop can only be prevented if cover crops are terminated early enough for replenishment of soil water.

Cover crop water consumption: Analysing performance of the agrometeorological model for the calculation of actual evapotranspiration (AMBAV) in a container experiment

“…A drainage layer at the bottom of each container allowed for the collection and quantification of leachate. ET m was determined using Equation () (Selzer & Schubert, 2023). …”

“…Plant height and LAI (ACCUPAR LP-80 PAR/LAI Ceptometer; METER Group) were measured weekly. Since the length of the LAI sensor exceeded the width of the containers, LAI had to be corrected with a transformation factor of 2.14 (Selzer & Schubert, 2023).…”

“…The objective of this study was to investigate whether AMBAV is suitable to accurately simulate cover crop water losses in the form of ET. Simulated ET (ET AMBAV ) was compared with measured ET (ET m ) from a cover crop experiment conducted under semi-controlled conditions in container technology in 2020 and 2021 (Selzer & Schubert, 2023). We hypothesized that there were no significant differences between ET m and ET AMBAV .…”

“…The increasingly common practice of cover cropping—the cultivation of crops in otherwise fallow periods to reduce nutrient losses—might intensify the drought stress for a succeeding cash crop as cover crops consume up to 270 mm water during their vegetation period (Selzer & Schubert, 2023). This is a major concern for farmers who have to choose between the benefits of cover cropping and cash crop yields (Mase et al, 2017; Woods et al, 2017; Zinngrebe et al, 2017).…”