Above ground biomass and water use efficiency of crops at shallow water tables in a temperate climate

Abstract

The objective of the paper was to quantify the water use efficiency (WUE) of different crops on lowland soils. This is relevant to agriculture for effective growing of bioenergy plants and sequestering carbon in plant biomass and soils. On two groundwater lysimeter stations in the vicinity of Berlin, Germany, a long-term study has been conducted. Above ground biomass, evapotranspiration (ET), proportion of subirrigated water and water use efficiency have been measured on soils of different texture. To quantify the effect of different water tables on crop biomass, additionally plant biomass production has been measured on surrounding farm plots. The climate was characterized by a mean temperature of 9.4 °C and an annual precipitation of 500–600 mm during the period of study. Subirrigation water requirements strongly depended on water table depths, crops and soil texture and showed a large variability between different years due to weather conditions. Spring barley consumed 10–60 mm of groundwater, winter wheat 20–250 mm, pasture and meadow grasses 80–300 mm, maize 100–400 mm, reed canary grass 400–900 mm, sedges 600–1000 mm and common reed 700–1200 mm. The ET in terms of the crop coefficient coincided with common recommendations, except from wetland plants, where it was higher than those. ET and above ground biomass were clearly crop-specific correlated. Plant type associated with appropriate water table depth, fertilization level and soil fertility were crucial factors of WUE. Results showed possible high dry matter biomass at all water table levels, but increasing WUE with deeper water tables when growing arable crops. Maize had the highest WUE with 4–6 g dry matter per l of water, followed by winter wheat, with a WUE of about 3. Wetland plants also produced high amounts of biomass but consumed more water. Their WUE was less than 1.5. Field plots had lower drainage and subirrigation intensity than lysimeters and thus indicated both waterlogging and drought stress. This resulted in significant and strong correlations between groundwater table and biomass of arable crops. As in lysimeters, the highest WUE occurred with the highest crop biomass, it may be concluded that in field situations, highest WUE can be achieved with controlling an optimum range of water table. Crops of highest WUE, maize and winter wheat, had optimum water tables in the range of 80–160 cm on soils of higher water storage capacity. Grassland required water tables less than 80 cm. Creating rewetted areas of water tables less than 20 cm would mean a very low efficiency of water use.