Zhenwei Song

Distribution and Trends in Reference Evapotranspiration in the North China Plain

The distribution and trends in reference evapotranspiration ( ETo ) are extremely important to water resources planning for agriculture, and it is widely believed that rates of ETo will increase with global warming. This is a big concern in China, where water deficits are common in the North China Plain (NCP). In this study, Penman-Monteith reference evapotranspiration at 26 meteorological stations during 1961–2006 in and around the NCP was calculated. The temporal variations and spatial distribution of ETo were analyzed and the causes for the variations were discussed. The results showed that: (1) the NCP was divided into two climatic regions based on aridity values: a semiarid region that accounts for 69% of the area and subhumid regions that made of the remaining area; (2) over the entire NCP, the highest annual ETo occurred in the central and western areas and the lowest total ETo was observed in the east. Comparing the mean monthly ETo and annual ETo distributions, the high ETo values from May throug...

Climatic warming increases winter wheat yield but reduces grain nitrogen concentration in east China.

Climatic warming is often predicted to reduce wheat yield and grain quality in China. However, direct evidence is still lacking. We conducted a three-year experiment with a Free Air Temperature Increase (FATI) facility to examine the responses of winter wheat growth and plant N accumulation to a moderate temperature increase of 1.5°C predicted to prevail by 2050 in East China. Three warming treatments (AW: all-day warming; DW: daytime warming; NW: nighttime warming) were applied for an entire growth period. Consistent warming effects on wheat plant were recorded across the experimental years. An increase of ca. 1.5°C in daily, daytime and nighttime mean temperatures shortened the length of pre-anthesis period averagely by 12.7, 8.3 and 10.7 d (P<0.05), respectively, but had no significant impact on the length of the post-anthesis period. Warming did not significantly alter the aboveground biomass production, but the grain yield was 16.3, 18.1 and 19.6% (P<0.05) higher in the AW, DW and NW plots than the non-warmed plot, respectively. Warming also significantly increased plant N uptake and total biomass N accumulation. However, warming significantly reduced grain N concentrations while increased N concentrations in the leaves and stems. Together, our results demonstrate differential impacts of warming on the depositions of grain starch and protein, highlighting the needs to further understand the mechanisms that underlie warming impacts on plant C and N metabolism in wheat.

Higher yields and lower methane emissions with new rice cultivars

Breeding high-yielding rice cultivars through increasing biomass is a key strategy to meet rising global food demands. Yet, increasing rice growth can stimulate methane (CH4 ) emissions, exacerbating global climate change, as rice cultivation is a major source of this powerful greenhouse gas. Here, we show in a series of experiments that high-yielding rice cultivars actually reduce CH4 emissions from typical paddy soils. Averaged across 33 rice cultivars, a biomass increase of 10% resulted in a 10.3% decrease in CH4 emissions in a soil with a high carbon (C) content. Compared to a low-yielding cultivar, a high-yielding cultivar significantly increased root porosity and the abundance of methane-consuming microorganisms, suggesting that the larger and more porous root systems of high-yielding cultivars facilitated CH4 oxidation by promoting O2 transport to soils. Our results were further supported by a meta-analysis, showing that high-yielding rice cultivars strongly decrease CH4 emissions from paddy soils with high organic C contents. Based on our results, increasing rice biomass by 10% could reduce annual CH4 emissions from Chinese rice agriculture by 7.1%. Our findings suggest that modern rice breeding strategies for high-yielding cultivars can substantially mitigate paddy CH4 emission in China and other rice growing regions.

Impacts of Nighttime Warming on the Soil Nematode Community in a Winter Wheat Field of Yangtze Delta Plain, China

Abstract Changes in the soil nematode community induced by global warming may have a considerable influence on agro-ecosystem functioning. However, the impacts of predicted warming on nematode community in farmland (e.g., winter wheat field) have not been well documented. Therefore, a field experiment with free air temperature increase (FATI) was conducted to investigate the responses of the soil nematode community to nighttime warming in a winter wheat field of Yangtze Delta Plain, China, during 2007 to 2009. Nighttime warming (NW) by 1.8°C at 5-cm soil depth had no significant impact on the total nematode abundance compared to un-warmed control (CK). However, NW significantly affected the nematode community structure. Warming favored the bacterivores and fungivores, such as Acrobeles, Monhystera, Rhabditis, and Rhabdontolaimus in bacterivores, and Filenchus in fungivores, while the plant-parasites were hindered, such as Helicotylenchus and Psilenchus. Interestingly, the carnivores/omnivores remained almost unchanged. Hence, the abundances of bacterivores and fungivores were significantly higher under NW than those under CK. Similarly, the abundances of plant-parasites were significantly lower under NW than under CK. Furthermore, Wasilewska index of the nematode community was significantly higher under NW than those under CK, indicating beneficial effect to the plant in the soil. Our results suggest that nighttime warming may improve soil fertility and decrease soil-borne diseases in winter wheat field through affecting the soil nematode community. It is also indicated that nighttime warming may promote the sustainability of the nematode community by altering genera-specific habitat suitability for soil biota.

Farming systems in China: Innovations for sustainable crop production

Abstract The progresses and experiences of grain production in China, the world’s largest grain producer, importer and consumer, are reviewed with emphasis on recent innovations. Farming systems are outlined, and the abiotic conditions and limitations to crop production are summarized, including historical changes in climate and soil. We analyze the contributions of genetic improvement to the yield of rice, wheat and maize and the underlying changes in phenotype. Agronomic innovations are presented, including reduced tillage, straw and plastic mulching, cropping season optimization, alternate dry-wetting irrigation for nursery and established rice crops, and site-specific nitrogen management. Responses and adaptations of major grain crops to realized and projected warming are discussed, including the expansion and re-drawing of cropping geographical boundaries. China has increased grain production continuously over recent decades but there are concerns with the secondary effects of intensive cropping on the environment, particularly farmland soil and water. Crop physiology, integrated with crop breeding and agronomy, will contribute to further innovations required for sustainable production.

Technological challenges to irrigation scheduling – Crop Coefficients, ETo forecasts, and in-situ ET measurements

ET-based irrigation scheduling has grown considerably in recent decades as the technology to collect data and disseminate information has improved. A huge advance occurred with the publication of the ASCE-EWRI standardized reference ET (ETref) equations, which provided an equation to account for weather effects on ET by quantifying evaporative demand. Well-watered crop evapotranspiration (ETc) is estimated as the product of ETref and an appropriate crop coefficient (Kc) value that accounts for the difference in ET between the reference and crop surfaces. The estimation of ETc is an important goal for irrigation researchers, but advances are difficult to make because of climate and irrigation management effects on Kc values. For efficient irrigation management, there is also a need to account for water and salinity stress effects on the actual crop evapotranspiration (ETa) when computing irrigation schedules. Many plant physiologists are investigating the use of plant-based measurements for regulated deficit irrigation of orchard and vine crops. ET information, however, is still necessary to properly interpret the plant-based measurements and to modify the irrigation management. In urban irrigation, water is applied rapidly and runoff is often the limiting factor determining irrigation timing and amount. Drip irrigated and shallow rooted crops are also frequently irrigated, so near-real time and forecast ETc estimates are needed to optimize irrigation management. In this paper, information on Kc research in California, ETo forecasts, and in-situ ET measurements is presented.