Assessing the effects of drought on rainfed maize water footprints based on remote sensing approaches.

BACKGROUND: Drought affects the characteristics of water use during crop production and so quantitatively evaluating the impacts is important. However, it remains unclear how crop water use responds to drought. To address this gap, water footprint (WF) and standardized precipitation evapotranspiration index (SPEI) were calculated by remote sensing approaches to assess the effects of drought on crop water use. Rainfed maize is the most important crop in Jilin Province, and its growth and water use are more susceptible to drought. The present study explored not only the impact of growing season drought on the maize WF values in Jilin Province, but also the response of WF values to drought at different time scales. RESULTS: Spatially, 72.94% of the WFblue pixels showed a non-significant increase, and the WFgreen in 68% pixels decreased significantly, being mainly concentrated in the middle region. Furthermore, the pixels affected by monthly time scale drought were mainly in the middle region, whereas the pixels affected by annual time scale drought were mainly in the western region. CONCLUSION: Drought not only affected on the source and structure of agricultural water consumption, but also had different effects on WF values at different time scale. These effects had obvious spatial differences. The present study systematically explored the effects of drought on the WF values for rainfed maize in different climate regions and a consideration of these effects could provide valuable information on rainfed maize growth and the agricultural water use response to a changing climate. © 2023 Society of Chemical Industry.

In situ 13CO2 labeling reveals that alpine treeline trees allocate less photoassimilates to roots compared with low-elevation trees.

Carbon (C) allocation plays a crucial role for survival and growth of alpine treeline trees, however it is still poorly understood. Using in situ 13CO2 labeling, we investigated the leaf photosynthesis and the allocation of 13C labeled photoassimilates in various tissues (leaves, twigs and fine roots) in treeline trees and low-elevation trees. Non-structural carbohydrate concentrations were also determined. The alpine treeline trees (2000 m. a.s.l.), compared with low-elevation trees (1700 m a.s.l.), did not show any disadvantage in photosynthesis, but the former allocated proportionally less newly assimilated C belowground than the latter. Carbon residence time in leaves was longer in treeline trees (19 days) than that in low-elevation ones (10 days). We found an overall lower density of newly assimilated C in treeline trees. The alpine treeline trees may have a photosynthetic compensatory mechanism to counteract the negative effects of the harsh treeline environment (e.g., lower temperature and shorter growing season) on C gain. Lower temperature at treeline may limit the sink activity and C downward transport via phloem, and shorter treeline growing season may result in early cessation of root growth, decreases sink strength, which all together lead to lower density of new C in the sink tissues and finally limit the growth of the alpine treeline trees.

Assessing the hotspots of crop water footprint in Jilin Province of China.

Water is one of the important key biophysical factors determining crop production. The increasing demand for crop products has placed substantial pressures on water resources and then led to a series of water issues. To shed light on multiple water issues in crop production, taking water footprint (WF) as a measurement, a WF hotspot index system including green water scarcity (GWS), blue water scarcity (BWS), water pollution level (WPL), water use efficiency ratio (WUER), and water use benefit ratio (WUBR) was constructed, and an empirical study was conducted to assess the WF hotspots of crop production in Jilin Province. Multiple types of hotspots exhibited obvious differences in spatio-temporal distribution. Hotspots of BWS and WPL were concentrated in the middle and western subregions and the grades of hotspots were higher in the drought and normal years. BWS and WPL had the same changing trend, showing superimposed distribution in space. Hotspots of GWS and WUBR occurred in most prefectures, whereas there were more WUBR hotspots and fewer GWS hotspots in the humid year. The hotspots of WUER were scattered in fewer prefectures with no obvious differences in different rainfall years. The water issues in the middle and western subregions were various and the grades of hotspots were higher than those in eastern subregion. The results of this study would contribute to comprehensively understanding various water issues during crop production and providing more information for sustainable agricultural water management.

Suitable chemical fertilizer reduction mitigates the water footprint of maize production: evidence from Northeast China.

Long-term excessive use of chemical fertilizer has led to water environmental degradation. Reducing chemical fertilizer use in crop production has become a consensus, and the effects of chemical fertilizer reduction on yield, water consumption and water environment urgently need to be explored. A field experiment including four fertilization treatments: normal fertilizer application (NFA), 15%, 30% and 45% fertilizer reduction (FR) was conducted and the water footprint (WF) was used as an indicator to explore how the chemical fertilizer reduction affected the maize WF. The results showed that the blue, green and total WFs of maize in the 45% FR and NFA treatments were larger than those in the 30% FR and 15% FR treatments in 2018 and 2019. The grey WFs of maize in the NFA treatment were the highest in 2018 and 2019, exhibiting a trend that the grey WFs in the NFA treatment >15% FR treatment >30% FR treatment >45% FR treatment in 2018 and those in the NFA treatment >45% FR treatment >30% FR treatment >15% FR treatment in 2019. The optimal treatment was the 15-30% FR compared with the current fertilization, in which the total WF of maize can be minimized and the maize yield can be maximized at the same time. Precipitation had a wide-ranging impact on the yield and WF of maize, especially the amount, intensity and interval of rainfall, which had an evident impact on the grey WF. This study is expected to provide a data foundation for reducing chemical fertilizer and improving water and fertilizer use efficiency in maize production.

Multi-source data-based spatial variations of blue and green water footprints for rice production in Jilin Province, China.

Rice production consumes more water than the production of other crop species due to the specific growth requirements of this species. Accurately accounting for water consumption during rice production and analyzing the spatio-temporal changes in water consumption are thus necessary. Using the water footprint (WF) as an indicator and combining data from multi-sources, this paper explored the regional differences in rice WFs in Jilin Province at a spatial resolution of 1 km. The results showed that the blue WF was always larger than the green WF, and the total, green and blue WFs were lowest during the humid year. The pixels with high values of total, green and blue WFs were mainly distributed in the eastern region of Jilin Province. Compared with the traditional estimation of the WF based on the data of administrative regions, RS techniques can overcome the administrative boundary and provide near real-time data concerning specific agricultural parameters to extract more accurate results for WF models. The combination of RS data and statistical, observational, and survey data can thus overcome the limitations of weather conditions affecting RS, reduce the incorporation of parameters, and estimate WFs quickly and accurately. This study provides a framework to evaluate crop WFs with multi-source data.