1,343 publications from this institution
Stable water isotopes have been used extensively to study the water use strategy of plants in various ecosystems. In deep vadose zone (DVZ) regions, the rooting depth of trees can reach several meters to tens of meters. However, the existence of roots in deep soils does not necessarily mean the occurrence of root water uptake, which usually occurs at a particular time during the growing season. Therefore, quantifying the contribution of deep-layer soil water (DLSW) in DVZ regions using the natural abundance of stable water isotopes may not be accurate because this method assumes that trees always extract shallow- and deep-layer soil water. We propose a multi-step method for addressing this issue. First, isotopic labeling in deep layers identifies whether trees absorb DLSW and determines the soil layer depths from which trees derive their water source. Next, calculate water sources based on the natural abundance of stable isotopes to quantify the water use strategy of trees. We also compared the results with the natural abundance of stable water isotopes method. The 11- and 17-year-old apple trees were taken as examples for analyses on China’s Loess Plateau. Isotopic labeling showed that the water uptake depth of 11-year-old apple trees reached 300 cm in the blossom and young fruit (BYF) stage and only 100 cm in the fruit swelling (FSW) stage, whereas 17-year-old trees always consumed water from the 0–320 cm soil layer. Overall, apple trees absorbed the most water from deep soils (> 140 cm) during the BYF stage, and 17-year-old trees consumed more water in these layers than 11-year-old trees throughout the growing season. In addition, the natural abundance of stable water isotopes method overestimated the contribution of DLSW, especially in the 320–500 cm soil layer. Our findings highlight that determining the occurrence of root water uptake in deep soils helps quantify the water use strategy of trees in DVZ regions.
The growth and seed yield of 5 vetch (Vicia) cultivars representing Vicia sativa, V. benghalensis and V. villosa were compared at 8 sites over 2 years in south-western Australia. The vetches showed considerable potential as grain and forage legume crops in the low to medium rainfall areas of the Western Australian cereal belt. Cultivars of V. sativa showed the most potential in terms of dry matter and seed yield, and on average across sites and seasons both Languedoc and Blanchefleur produced over 2.5 t/ha of dry matter at flowering: Machine-harvested seed yields were over 1.6 t/ha. Cultivars of V. benghalensis and V. villosa produced considerably less dry matter at flowering and had lower harvest index (0.14-0.42) and seed yield < 4 t/ha) when compared with the V. sativa cultivars, possibly due to their poor growth rates and delayed phenology. Early Purple, an early flowering and maturing selection from the V. benghalensis cultivar Popany, showed improved adaptation and seed yield at many low rainfall sites. Nevertheless, Languedoc, Blanchefleur and Early Popany are all considered late flowering (up to 126 days) compared with grain legumes adapted to this environment, and further improvement in vetch species could be achieved by selecting for more rapid development. Both soft-seededness and non-shattering pods should also be high priorities for vetch selection and/or breeding programs. It is concluded that vetch species may have a role in farming systems in Western Australia for the production of fodder, hay, grain or green manure while providing the other rotational benefits of legumes on fine-textured neutral to alkaline and shallow duplex soils where narrow-leafed lupin is poorly adapted.
Resources of arable land and irrigation water available in the world are diminishing while the population contin- ues to increase. This situation has contributed to chronic malnutrition and starvation in times of crisis. While the twin problems of overpopulation and unequal distribution of food between rich and poor people are political prob- lems, increasing the supply of food from the existing resources of land and water is a problem that can be ad- dressed by agronomists. It is widely recognised that average farm yields of rainfed crops, even in developed coun- tries, seldom exceed half of the theoretical potential yield if all the rain is used efficiently. It is proposed that this gap between actual and potential grain yield can be effectively addressed using existing technologies that do not destroy soil fertility, and may even improve it. This paper discusses the contributions that agronomists are making and can make in the future to increase the yields of rainfed crops. Agronomic practices that can improve yield and the management of soil resources that will sustain such improvements in the longer term are inter-linked. The in- creasing use and benefits of conservation agriculture, the benefits of rotating crops, especially with legumes, and the possibility of improving crop yields through diagnosing and treating the factors limiting production are dis- cussed.
