Drought-Tolerant Barley: I. Field Observations of Growth and Development

An ever-growing challenge to agricultural production worldwide is the reduced availability of water and increased incidence of drought. The development of low-irrigation barley cultivars marks a significant achievement in breeding efforts for drought tolerance, but specific traits conferring adaptation to water stress remain unclear. Here, we report results from two years of replicated field trials comparing yield, phenology, water usage, and rooting characteristics of low-irrigation varieties “Solar” and “Solum” to high-input, semi-dwarf varieties “Kopious” and “Cochise”. The objective was to identify differential performance of varieties under high- and low-water conditions through comparison of growth and developmental traits. Rooting characteristics were analyzed by digging in-field root profile walls to a depth of 1.8 m. Varieties were compared under high (877 mm) and low (223 mm) water regimes including irrigation and precipitation. Observed traits associated with improved performance of the low-irrigation varieties under drought conditions included early vigor, early flowering, greater root growth at 40–80 cm depth, and more effective water use exhibited by greater water extraction post-anthesis. The deeper rooting pattern of the low-irrigation varieties may be related to their ability to use more water post-anthesis under water stress, and thus, to fill grain, compared to high input varieties.

Vertical distribution of fine-root area in relation to stand age and environmental factors in black locust (Robinia pseudoacacia) forests of the Chinese Loess Plateau

To examine the spatiotemporal characteristics of the distribution of fine-root area and its relationship with stand age and environmental factors in black locust (Robinia pseudoacacia L.) on the Chinese Loess Plateau, black locust stands were selected at four sites along a precipitation gradient. Four stands of different ages and a transect along the hillslope were also selected at one of the sites. With increasing stand age, fine-root area at the tree level increased exponentially, and the rooting pattern tended to be deeper for trees up to 15 years old and then shallower thereafter. The temporal changes of fine-root distribution could be quantified using stand age and soil nutrients. At the hillslope scale, fine-root area index (FRAI) was lower while the rooting pattern was deeper in the middle slope than in the upper and lower slopes, and the fine-root distribution could be quantified using elevation and soil properties. At the regional scale, FRAI decreased substantially while exhibiting similar rooting patterns with decreasing soil water and nutrient availability along the precipitation gradient. Humidity index represented the regional environmental variation and could be used to quantify FRAI. These findings will be helpful for improving quantification of fine roots and enhancing the accuracy of ecohydrological models.

Growth of three oak species during establishment of an agroforestry practice for watershed protection

Tree species that provide early benefits for farmers can serve to increase the adoption of temperate agroforestry practices. Growth of pin (Quercus palustris Muenchh.), swamp white (Quercus bicolor Willd.), and bur oak (Quercus macrocarpa Michx.) saplings was evaluated in an agroforestry practice designed for watershed protection in northern Missouri, USA, to identify species that provide early productive and protective functions. Large, containerized oak seedlings were planted in the center of 4.5-m-wide contour grass-legume strips established at 22.8- to 36.5-m intervals on a 4.44-ha watershed with a corn (Zea mays L.) – soybean (Glycine max (L.) Merr.) rotation. Sapling survival, height, and diameter growth were annually recorded during five growing seasons. Branch and leaf mass were also recorded in the two last measuring years. Preliminary assessment of rooting pattern was made based on the relative abundance of horizontal and vertical main roots. Mean shoot growth rate of pin oak was the highest during the whole study period, while swamp white and bur oak grew at the same rate until the fourth growing season. During the fifth growing season, growth rate of bur oak was the lowest. The root system of pin oak appears to be concentrated close to the tree, thus strengthening the buffer strips and competing least with the crop. The shallow root system of swamp white oak may best scavenge leaching nutrients from subsurface flow, thus reducing nonpoint source pollution. Sapling survival, growth rate, and rooting pattern suggest that pin oak and swamp white oak have a better potential for agroforestry practices in the Midwest than bur oak.

Water balance of annual and perennial pastures on a duplex soil in a Mediterranean environment

Dryland salinity in southern Australia is largely due to inadequate water use by annual agricultural crops and pastures. Perennial pastures, such as lucerne, have been proposed as a possible means of increasing water use whilst maintaining flexibility in agricultural rotations. In a trial located on a duplex soil near Katanning, Western Australia, lucerne and subterranean clover pastures both used water at rates indistinguishable from potential evapotranspiration during the winter and early spring of 3 consecutive years (1995–97), and completely exhausted water stored in the A horizon. Lucerne, through a deeper rooting pattern and by maintaining activity in the summer and autumn, used approximately 50 mm more water than the annual pasture during each 12-month period. This resulted in reduced deep drainage below 1.2 m in the 1996 season (30 mm compared with 80 mm under annual pasture). With average regional groundwater recharge in the range 10–50 mm, the reductions in drainage observed under lucerne show promise in reducing the regional impact of dryland salinity.