Xinmei Hao

Effects of root density distribution models on root water uptake and water flow under irrigation

Water uptake by roots greatly influences water distributions in soil-plant systems. It is essential to understand root water uptake patterns to estimate accurately water movement through the systems. In this study, six empirical root density distribution models were incorporated into a water flow model to study their effect on root water uptake and soil water movement. Two main distributions of root systems, i.e., cylindrical and conical shapes, were considered. Root water uptake with these models was evaluated at three levels of irrigation, about 0.3, 0.7 and 1.0 of total potential transpiration, with three root depths in a sandy loam soil and a silt loam soil. High irrigation levels reduced difference of root water uptake from different root depths in both soils. In the sandy loam soil, a shallow root depth could enhance difference in root water uptake among different root distribution models, whereas a greater difference was found within larger root depths in the silt loam soil. The models with the conical shape resulted in an average of 13% higher leaching in the sandy loam soil than were seen with the cylindrical shape. Contributions from different parts of the root system to the total root water uptake were varied with the different models, as were the distributions of water pressure head and water flux in the soil profiles.

Spatial Variability of Grapevine Bud Burst Percentage and Its Association with Soil Properties at Field Scale

There is a growing interest in precision viticulture with the development of global positioning system and geographical information system technologies. Limited information is available on spatial variation of bud behavior and its possible association with soil properties. The objective of this study was to investigate spatial variability of bud burst percentage and its association with soil properties based on 2-year experiments at a vineyard of arid northwest China. Geostatistical approach was used to describe the spatial variation in bud burst percentage within the vineyard. Partial least square regressions (PLSRs) of bud burst percentage with soil properties were used to evaluate the contribution of soil properties to overall spatial variability in bud burst percentage for the high, medium and low bud burst percentage groups. Within the vineyard, the coefficient of variation (CV) of bud burst percentage was 20% and 15% for 2012 and 2013 respectively. Bud burst percentage within the vineyard showed moderate spatial variability, and the overall spatial pattern of bud burst percentage was similar between the two years. Soil properties alone explained 31% and 37% of the total spatial variation respectively for the low group of 2012 and 2013, and 16% and 24% for the high group of 2012 and 2013 respectively. For the low group, the fraction of variations explained by soil properties was found similar between the two years, while there was substantial difference for the high group. The findings are expected to lay a good foundation for developing remedy measures in the areas with low bud burst percentage, thus in turn improving the overall grape yield and quality.

Spatial Variation of Winegrape Yield and Berry Composition and their Relationships to Spatiotemporal Distribution of Soil Water Content

Spatiotemporal variability in vineyard soil water content (SWC) can affect yield and berry composition. The objectives of this study were to examine spatial variability in yield and berry composition over time and to quantify the contribution of spatial variability in SWC to these parameters. Yield, Brix, tannins, and total phenols were collected at the end of the berry ripening stage for 135 georeferenced points in 2012 and for 147 points in 2013 and 2014 in a Merlot vineyard in Gansu province, China. Volumetric SWC was measured multiple times at those points at different growth stages in each year. Spatial variation in yield showed moderate and similar spatial heterogeneity for different years, but the variation in berry composition was not consistent among years. Spatial variation in yield in 2012 and 2013 was best described by an exponential variogram model, but there was no spatial structure of yield in 2014. Low SWC at 0 to 20 cm depth corresponded to higher yield than did high SWC, and the opposite results were found for 40 to 60 cm. Spatiotemporal distribution of SWC explained more than 35% of total variation in yield and berry composition in the relatively dry year of 2012, but less than 10% in the relatively wet year of 2014. The contribution of spatiotemporal distributions of SWC to spatial variability in yield and berry composition varied according to field and weather conditions. This study provides a basis for developing site-specific management measures for better economic return.

Analysis and Trend Prediction of Water Utilization Structure in Haihe River Basin

Due to the human activities and climate change, the scarcity of water resources and the deterioration of water environment has been a serious problem in Haihe river basin. It is important to study water withdrawal and water utilization structure for sustainable use of water resources in this area. We analyzed the present water utilization structure of Haihe river basin by using the information entropy theory. Results show that water structure entropy value of Beijing and Tianjin is higher than other provinces in the basin and the whole basin, which matches the fact that the agricultural, industrial, domestic, and ecological water use are relatively balanced in Beijing and Tianjin while the proportion of agricultural water use is extremely large in other provinces of the basin. GM (1, 1) model and grey Markov model have been developed for simulation and predicting the evolution of water utilization structure in Haihe river basin. According to the results, the accuracy of grey Markov model was higher, which predicated the reduction of agricultural and industrial water consumption, and the increase of domestic and ecological water consumption in the future. Specifically, the model predicted that the proportion of water utilization structure in terms of ratio of agricultural, industrial, domestic, and ecological water use would change from 64.7:14.9:17.0:3.4 in 2011 to 63.4:12.2:20.2:4.2 in 2020, and the total water consumption will be reduced to 2.9 billion m3.

Earlier-Maturing Hybrids Improve Corn Grain Profitability in the Northern Corn Belt

With continuous genetic improvement of corn (Zea mays L.) hybrids and increasing volatility in energy cost, selecting hybrids with appropriate relative maturity (RM) ratings has significant impacts on profitability for growers. Annual grain yield and moisture at harvest of corn hybrids from 2000-2009 were obtained in three zones across Michigan. Hybrids were classified into either early- or latematuring groups based on their RM ratings, and the top 5 yielding hybrids of the two groups for each year in each zone were included in the analysis. The relative economic returns of the early- and late-maturing hybrids were evaluated using scenarios of various corn grain price and drying cost combinations. Overall, the late-maturing hybrids had higher grain yield than the early hybrids in the three zones, but only in two of the ten years was the yield difference statistically significant. Meanwhile, grain moisture was consistently and significantly higher for the late hybrids across the region. Consequently, the late hybrids had significantly larger net returns only when they had a large yield advantage combined with a corn grain price higher than

Improving agricultural water productivity to ensure food security in China under changing environment: From research to practice

3.5/bu and drying cost less than

Management Practice Effects on Surface Total Carbon: Differences in Spatial Variability Patterns

0.05/bu/point. For most of price and cost scenarios studied, the early-maturing hybrids had greater net returns than the late-maturing hybrids.