Monitoring and modeling of water and related nutrient fluxes in rice-based cropping systems
Final Report Abstract
SP7 developed a high-resolution automatic sampling system for continuous in situ measurements of stable water isotopic composition and nitrogen solutes along with hydrological information to improve our understanding of hydrological processes in agricultural production systems such as rice paddies. We also used manually collected water, soil and plant samples to investigate the effects of flooding/non flooded conditions and crop diversification on plant root water uptake depths. Measurements within a developed framework allowed us to estimate that the location for root water uptake of rice depends on the irrigation regime. The main water source for wet rice transpiration was surface water (~56–72 %) followed by soil water (~17–19 %) directly below the surface (0–0.02 m) during crop growth without seasonal differences. Dry rice extracted ~40–50 % of its water from shallow soil (0–0.5 m) with a subsequently larger contribution of up to 35 % from deeper soil horizons when the plants approach maturity. Rice plants extracted water proportionally to the root length density and soil water contents along the depth. The relative contributions of the soil water sources to root water uptake decreased with depth and reflected the exponential shape of the root density profile. During the dry seasons, the main water source for root water uptake was often based on irrigation while during the wet seasons, rainfall played an important role in plant water uptake. Water productivity of wet rice, could be further improved if the water ponding depth was reduced to a constant 0.015 m water level instead of water table fluctuations due to irregular irrigation. This management practice may save up to 30% irrigation water during the WS 2015 and up to 44 % during the DS 2016. Therefore, having a better understanding of where rice plants take up their water, proper water-saving irrigation management systems can be developed. Overall, groundwater is primarily a mixture of irrigation and rainwater, where the main driver is irrigation water during the dry season and rainwater during the wet season. We estimate significantly higher evaporation (63-77%) during the dry season as compared to the wet season (27-36%). Shallow groundwater under tropical agricultural fields is affected by evaporation. The influence is stronger in wet and dry rice and less for maize. The groundwater during the dry season under wet and dry rice fields is dominated at the beginning of the growing season mainly by the input of rainwater, later the groundwater is more and more replenished by irrigation water. Groundwater under dry-season maize reacts rapidly on irrigation, indicating preferential flow processes via cracks and deep roots. We also found, for the first time, significant sub-daily isotopic variation in groundwater and surface ponded water, with an isotopic enrichment during the daytime. High correlations with relative humidity and temperature explain part of this variability. Further, the day-night isotopic difference in surface water is driven by temperature and relative humidity, however, the groundwater changes are independent from these atmospheric conditions.
Publications
- (2013) Set up of an automatic water quality sampling system in irrigation agriculture. Sensors 14, 212–228
Heinz E, Kraft P, Buchen C, Frede H-G, Aquino E, Breuer L
(See online at https://doi.org/10.3390/s140100212) - (2018) High-frequency water isotopic analysis using an automatic water sampling system in rice-based cropping systems. Water 2018,10, 1327
Mahindawansha A, Breuer L, Chamorro C, Kraft P
(See online at https://doi.org/10.3390/w10101327) - (2018) Quantification of plant water uptake by water stable isotopes in rice paddy systems. Plant and Soil 429, 281-302
Mahindawansha A., Orlowski N., Kraft P., Rothfuss Y., Racela H., Breuer L.
(See online at https://doi.org/10.1007/s11104-018-3693-7)
