Fingerprint of rice paddies in spatial-temporal dynamics of atmospheric methane concentration in monsoon Asia.

Agriculture (e.g., rice paddies) has been considered one of the main emission sources responsible for the sudden rise of atmospheric methane concentration (XCH4) since 2007, but remains debated. Here we use satellite-based rice paddy and XCH4 data to investigate the spatial-temporal relationships between rice paddy area, rice plant growth, and XCH4 in monsoon Asia, which accounts for ~87% of the global rice area. We find strong spatial consistencies between rice paddy area and XCH4 and seasonal consistencies between rice plant growth and XCH4. Our results also show a decreasing trend in rice paddy area in monsoon Asia since 2007, which suggests that the change in rice paddy area could not be one of the major drivers for the renewed XCH4 growth, thus other sources and sinks should be further investigated. Our findings highlight the importance of satellite-based paddy rice datasets in understanding the spatial-temporal dynamics of XCH4 in monsoon Asia

Global-scale modeling of nitrogen balances at the soil surface

This paper provides global terrestrial surface balances of nitrogen (N) at a resolution of 0.5 by 0.5 degree for the years 1961, 1995 and 2050 as simulated by the model WaterGAP-N. The terms livestock N excretion (Nanm), synthetic N fertilizer (Nfert), atmospheric N deposition (Ndep) and biological N fixation (Nfix) are considered as input while N export by plant uptake (Nexp) and ammonia volatilization (Nvol) are taken into account as output terms. The different terms in the balance are compared to results of other global models and uncertainties are described. Total global surface N surplus increased from 161 Tg N yr-1 in 1961 to 230 Tg N yr-1 in 1995. Using assumptions for the scenario A1B of the Special Report on Emission Scenarios (SRES) of the International Panel on Climate Change (IPCC) as quantified by the IMAGE model, total global surface N surplus is estimated to be 229 Tg N yr-1 in 2050. However, the implementation of these scenario assumptions leads to negative surface balances in many agricultural areas on the globe, which indicates that the assumptions about N fertilizer use and crop production changes are not consistent. Recommendations are made on how to change the assumptions about N fertilizer use to receive a more consistent scenario, which would lead to higher N surpluses in 2050 as compared to 1995

Detection and attribution of nitrogen runoff trend in China's croplands

Reliable detection and attribution of changes in nitrogen (N) runoff from croplands are essential for designing efficient, sustainable N management strategies for future. Despite the recognition that excess N runoff poses a risk of aquatic eutrophication, large-scale, spatially detailed N runoff trends and their drivers remain poorly understood in China. Based on data comprising 535 site-years from 100 sites across China's croplands, we developed a data-driven upscaling model and a new simplified attribution approach to detect and attribute N runoff trends during the period of 1990–2012. Our results show that N runoff has increased by 46% for rice paddy fields and 31% for upland areas since 1990. However, we acknowledge that the upscaling model is subject to large uncertainties (20% and 40% as coefficient of variation of N runoff, respectively). At national scale, increased fertilizer application was identified as the most likely driver of the N runoff trend, while decreased irrigation levels offset to some extent the impact of fertilization increases. In southern China, the increasing trend of upland N runoff can be attributed to the growth in N runoff rates. Our results suggested that increased SOM led to the N runoff rate growth for uplands, but led to a decline for rice paddy fields. In combination, these results imply that improving management approaches for both N fertilizer use and irrigation is urgently required for mitigating agricultural N runoff in China

Chapter 5: Food Security

The current food system (production, transport, processing, packaging, storage, retail, consumption, loss and waste) feeds the great majority of world population and supports the livelihoods of over 1 billion people. Since 1961, food supply per capita has increased more than 30%, accompanied by greater use of nitrogen fertilisers (increase of about 800%) and water resources for irrigation (increase of more than 100%). However, an estimated 821 million people are currently undernourished, 151 million children under five are stunted, 613 million women and girls aged 15 to 49 suffer from iron deficiency, and 2 billion adults are overweight or obese. The food system is under pressure from non-climate stressors (e.g., population and income growth, demand for animal-sourced products), and from climate change. These climate and non-climate stresses are impacting the four pillars of food security (availability, access, utilisation, and stability)

Greenhouse gas budgets of crop production : current and likely future trends

Publisher PD

World’s Demand for Food and Water: The Consequences of Climate Change

This study focused on analysis of global food demand and supply situation by 2030 and 2050, water demand-availability, impact of climate change on world water resource, food security and desalination challenges and development opportunities. The population of the world will be 8.6 billion in 2030 and 9.8 billion in 2050; Africa will be the major contributor. World cereal equivalent (CE) food demand is projected to be around 10,094 million tons in 2030 and 14,886 million tons in 2050, while its production is projected to be 10,120 million tons in 2030 and 15,970 million tons in 2050 having a marginal surplus. India and China are capturing large share of global food demand. The developing country will demand more animal origin foods due to income growth in the future. The growth rate of world demand for cereals will decline till 2050. Global water demand is projected to increase by 55% between 2000 and 2050 from 3500 to 5425 km3. Evidence showed that climate change will have adverse impact on world water resources and food production with high degree of regional variability and scarcity. A number of options are suggested for development of global water resource and food production

A Review of Soil-Improving Cropping Systems for Soil Salinization

A major challenge of the Sustainable Development Goals linked to Agriculture, Food Security, and Nutrition, under the current global crop production paradigm, is that increasing crop yields often have negative environmental impacts. It is therefore urgent to develop and adopt optimal soil-improving cropping systems (SICS) that can allow us to decouple these system parameters. Soil salinization is a major environmental hazard that limits agricultural potential and is closely linked to agricultural mismanagement and water resources overexploitation, especially in arid climates. Here we review literature seeking to ameliorate the negative effect of soil salinization on crop productivity and conduct a global meta-analysis of 128 paired soil quality and yield observations from 30 studies. In this regard, we compared the effectivity of different SICS that aim to cope with soil salinization across 11 countries, in order to reveal those that are the most promising. The analysis shows that besides case-specific optimization of irrigation and drainage management, combinations of soil amendments, conditioners, and residue management can contribute to significant reductions of soil salinity while significantly increasing crop yields. These results highlight that conservation agriculture can also achieve the higher yields required for upscaling and sustaining crop production

Increasing the productivity of sunflower through efficient use of non-saline and saline water irrigation in the Ganges Delta

Climate change and sea-level rise have caused increases in soil and water salinity and freshwater scarcity in Coastal Bangladesh in the Ganges delta. This has greatly increased the risks associated with dry season cropping. Therefore, increasing the productivity of dry season crops (like sunflower) depends on the proper management of non-saline and saline water irrigation. Three experiments were conducted, mostly in Khulna, Bangladesh, including (i) a surface and groundwater survey on salinity and water availability, (ii) determination of crop sensitivities to saline water irrigation through pot studies, and (iii) studies on the combined use of non-saline and saline irrigation water in field experiments. It is found that the salinity of canals and ponds started to increase after February and reached a maximum by mid-April. The salinity of ponds and groundwater was less than the salinity of rivers and canals (without bunds). Cumulative evaporation, water extraction and saline water intrusion were the most important factors increasing water salinity and decreasing the volume of stored water. Pot experiments showed that sunflower was most susceptible to salinity during flowering. Yield reductions were related to both a reduction in mature seed number and seed size. Yields were positively related to photosynthesis and negatively related to Na/K ratios. In the field, limited use of freshwater at the initial stages and increasing use of brackish/saline water at the latter stages increased the freshwater productivity of sunflower 4–fold. This freshwater productivity (FWP) concept is particularly suitable for the saline areas, to focus on increasing the value derived from the use of limited volumes of fresh water, supplementing this with the use of saline water. Increasingly negative solute potentials and increasing soil salinity (EC1:5) at 15–30 cm and 45–60 cm soil depths had the greatest adverse effects on the yield of sunflower in the field. Around 40–79% of the salt added in the irrigation water could not be accounted for in the 0–60 cm layer of soils suggesting that it moved to soil layers deeper. It is recommended that non-saline water be used to irrigate sunflowers when plants are most sensitive to salinity, but slightly to moderately saline water could be used at other growth stages without adversely affecting yield. The sustainability of this practice in the long term needs further investigation