Hydrological and plant growth changes in a small agricultural catchment: effects of inter-row soil management and land use types

Soil-plant-water monitoring allows stakeholders to obtain rapid information on plant stress caused by water or nutrient deficiencies. The main objective of the study was to investigate soil-plant-water interactions based on field measurements of plant reflectance and soil water content (SWC) under different land use types and inter-row managed vineyards. Four main study sites were investigated during the vegetation period: forest, grassland, cropland (sunflower), and vineyard. Three different soil management applications were studied in the vineyard: tilled (T), cover crops (CC), and grass (NT) inter-rows. SWCs were also measured within the row and between rows of vines to get a more complete picture of the hydrology of the sites. At each study site, we had several measurement points along a slope section, where each slope is prone to erosion. For continuous hydrological monitoring soil water and temperature sensors were placed 15 and 40cm below the ground at the top and bottom of the slopes. Normalized Difference Vegetation Index (NDVI) and Photochemical Reflectance Index (PRI) sensors were used to measure leaf reflectance. All sites included a set of hemispherical sensor sets. Topsoil SWC, leaf NDVI and chlorophyll concentrations, and Leaf Area Index (LAI) were measured every two weeks using hand-held instruments.

Among the four land use types, the lowest SWC and soil temperature of the upper 20cm was observed in the forest, and the highest in the cropland. The in-row average topsoil SWCs and temperatures were lower in all study sites compared to the values measured in between rows. The lowest chlorophyll and NDVI values were observed in grassland, which also showed the highest drought stress. The grassed inter-row grapevines had significantly lower leaf chlorophyll contents than the other inter-row managed sites (p<0.001). The highest leaf chlorophyll contents were observed in the forest samples (17.14CCI) and the tilled vineyard (16.89CCI). Based on slope positions, the most distinguishable difference was observed for the CC vineyard plants, 17.6% higher values were observed at the top of the slope compared to the leaves at the bottom of the slope (p<0.01). The leaf NDVI values were not influenced by slope positions for the vineyard, cropland, or forest. However, significantly higher chlorophyll and NDVI values were noted for the grassland lower points than the upper. The most distinguishable differences between lower and upper slope positions’ SWC values were observed for the tilled vineyard slope, 59.4% and 35.0% higher overall SWC were measured for the in-row and between-row, respectively. Overall LAI values were the highest for the forest and the lowest for the grassland, where slope position did not affect plant leaf areas significantly. The steadily decreasing annual precipitation amount (from 740mm to 422mm between 2016 and 2022) makes the area more vulnerable to climate change and highlights the need for future work on the applications of water retention measures.