Lamont D. Saunders

Automation of Subsurface Drip Irrigation for Crop Research

Automatic feedback control of precision irrigation scheduling allows the determination of optimum soil water potential for crops, close determination of N fertilizer requirements, and other measures of crop development and yield responses. Soil water potential (SWP) was measured with granular matrix sensors (GMS; Watermark Soil Moisture Sensors Model 200SS, Irrometer Co., Riverside, Calif., USA) at 0.2-m depth below onion and potato rows. Sensors were calibrated to SWP. The GMS were connected to a datalogger (CR10X datalogger, Campbell Scientific, Logan, Utah, USA) via five multiplexers (AM416 multiplexer, Campbell Scientific). The datalogger was programmed to read the GMS in each irrigation treatment zone 4 to 8 times a day and irrigate each zone individually as necessary. Irrigations were controlled by the datalogger signaling a controller (SDM-CD16AC controller, Campbell Scientific) connected to solenoid valves for each zone. The pressure in the drip lines was maintained at 69 kPa by a pressure regulator in each zone. The amount of water applied in each zone was recorded by a water meter installed between the solenoid valve and the drip tape. The irrigation criteria for onion (Allium cepa) and potato (Solanum tuberosum) were determined for subsurface drip irrigation (SDI). N fertilizer requirements may be reduced due to reduced N leaching under SDI.

Irrigation to Enhance Native Seed Production for Great Basin Restoration

ABSTRACT: Native shrublands and their associated grasses and forbs have been disappearing from the Great Basin as a result of grazing practices, exotic weed invasions, altered fire regimes, climate change and other human impacts. Native forb seed is needed to restore these areas. The irrigation requirements for maximum seed production of four key native forb species (Eriogonum umbellatum, Lomatium dissectum, Penstemon speciosus, and Sphaeralcea grossulariifolia) were studied at the Oregon State University Malheur Experiment Station beginning in 2005. Species plots were supplied with 0, 100, or 200 mm of subsurface drip irrigation per year using a randomized complete block design with four replications. Irrigation in each plot was divided into four equal increments applied between bud and seed set with timing dependent upon the flowering and seed set phenology of each species. Seed was harvested in each year of production through 2011, and the optimal irrigation rate was determined by regression. The four native forb species differed in their responses to irrigation. Lomatium dissectum seed yields were optimized with 140 mm of irrigation. Eriogonum umbellatum seed yields were optimized with 173 to 200 mm of irrigation in dry years and progressively less to no irrigation in the wettest year. Penstemon speciosus seed yields were optimized with 107 mm of irrigation in dry years and were reduced by irrigation in wet years. Sphaeralcea grossulariifolia seed yields did not respond to irrigation. Water requirements of these species are low, and these results can be used by seed growers to produce native forb seed more economically.

Irrigation Requirements for Seed Production of Two Eriogonum Species in a Semiarid Environment

Seeds of native plants are needed for rangeland restoration in the Intermountain West. Many of these plants are rarely cultivated and relatively little is known about the cultural practices required for their seed production. Irrigation trials were conducted over multiple years for two perennial Eriogonum species, Eriogonum umbellatum Torr. and Eriogonum heracleoides Nutt. The two species grown at the Oregon State University Malheur Experiment Station, Ontario, Ore., received 0, 100, or 200 mm·year of drip irrigation. Seed yield responses to irrigation were evaluated by linear and quadratic regression against 1) applied water; 2) applied water plus spring precipitation; 3) applied water plus winter and spring precipitation; and 4) applied water plus fall, winter, and spring precipitation. In general, seed yields responded quadratically to irrigation. For E. umbellatum, over 11 years, highest seed yields averaged 260 kg·ha and ranged from 207 to 508 kg·ha. ForE. heracleoides, over 6 years, highest yields averaged 353 kg·ha and ranged from 168 to 588 kg·ha. Adding spring precipitation to applied water improved the accuracy of estimated water requirements for maximum seed production of E. umbellatum. For E. heracleoides, adding precipitation to applied water did not improve the accuracy of estimated water requirements for maximum seed production. Averaged over 11 years, seed yield of E. umbellatum was maximized by 209 mm·year of spring precipitation plus irrigation. Averaged over 6 years, seed yield of E. heracleoides was maximized by 126 mm·year of applied water. Both species required relatively small amounts of irrigation to help assure seed yield, and the irrigation needed for E. umbellatum could be adjusted by taking spring precipitation into account. In the Intermountain West, native plant communities are being lost because of exotic plant invasions, changing fire regimes, and increasing human population pressure and activities (Balch et al., 2013; Liu and Wimberly, 2015). The National Seed Strategy (Plant Conservation Alliance, 2015) and other recent federal directives emphasize the use of native species to assist the recovery of degraded public lands. Native shrubs and grasses have long been used for revegetation following wildfires and other disturbances. A current priority is the addition of a greater number of native forbs to revegetation plantings that are designed to conserve sage-grouse habitat, increase pollinator populations (Dumroese et al., 2015), and reestablish native communities that are diverse and resilient following wildfire. Increasing the use of Eriogonum heracleoides Nutt. and E. umbellatum Torr. as well as other common buckwheat species necessitates development of cultural practices required for increase of their seed in agricultural settings, as wildland collections are expensive and generally inadequate to meet revegetation needs. For most forb species where seeds are in demand for restoration use in the Intermountain West, guidelines for seed production practices are not available (Cane, 2008; Shaw and Jensen, 2014). Eriogonum heracleoides (parsnipflower or Wyeth buckwheat) and E. umbellatum (sulphur-flower buckwheat) of the Polygonaceae family are low-growing, taprooted subshrubs that are widespread in the Rocky Mountains and Intermountain West with ivory and yellow flowers, respectively (Reveal, 2012). Both species are mat or clump-forming and produce upright flowering stems that support umbrella-like clusters of flowers. They commonly occur scattered among other vegetation on dry, exposed sites with well-drained soils and are common in rocky and sandy areas. E. heracleoides occurs from the sagebrush (Artemisia spp. L.) zone through open areas in aspen (Populus tremuloides Michx.) and other forested communities, whereas E. umbellatum grows in communities from the sagebrush to the subalpine zone (Reveal, 2012; Welsh et al., 1987). Eriogonum spp. are drought hardy and long-lived. Both species are recommended for plantings to provide pollinator habitat (Ogle et al., 2011). E. umbellatum provides food and habitat for sage-grouse (Bunnell et al., 2004; Pyle, 1993). Because of their low palatability, most perennial Eriogonum spp. are not considered valuable forage plants for wildlife or domestic livestock, but they are used to some extent in spring and fall when other forage may not be available (USDA Forest Service, 1937). Sheep seek out the flower clusters. Eriogonum spp. are useful for low-maintenance landscaping, xeriscaping, and rock garden plantings in urban areas, recreation sites, and along roadsides (Dyer et al., 2005; Parris et al., 2010; Tilley et al., 2007; Young-Mathews, 2012). They are attractive year-around, require little water and are easily maintained. Plants are semievergreen, and flower in early to midsummer after many other natives have completed their flowering cycle. The flowers are longlasting and remain colorful after drying on the plants (Meyer, 2008). Where adapted, Eriogonum spp. can add diversity to native seedings and are particularly valuable because of their ability to establish on disturbed sites resulting from activities including road construction or energy development. Once established, they can provide erosion control due to their mat-forming habit and natural spread. They may also serve as nurse plants that enhance establishment of later arriving species (Meyer, 2008). Practices that increase the reliability of seed production are needed to reduce grower risk. Although E. heracleoides and E. umbellatum generally occur in areas receiving low precipitation, recommendations for optimal amounts and timing of irrigation for individual species are needed to improve the reliability of seed production because seed production can be very low in dry years. Research has described the seed yield responses of five species of IntermountainWest perennial forbs of the genus Lomatium to irrigation and seasonal precipitation (Shock et al., 2016). Sprinkler or furrow irrigation encourages weeds and the spread of fungal pathogens. Subsurface drip irrigation reduces these problems by decreasing surface soil wetting. Reduction of weeds is a critical Received for publication 2 June 2017. Accepted for publication 26 July 2017. This project was partially funded by the USDA Forest Service, Rocky Mountain Research Station’s Great Basin Native Plant Project, USDI Bureau of Land Management, OR State University, Malheur County Education Service District, and by Formula Grants 2016-31100-06041 and 2016-31200-06041 from the USDA National Institute of Food and Agriculture. Director and Professor Emeritus. Senior Faculty Research Assistant. Bioscience Research Technician I. Bioscience Research Technician III. Research Botanist (Emeritus). Research Biologist. Corresponding author. E-mail: clinton.shock@ oregonstate.edu. 1188 HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 concern when growing native forbs as herbicides have not been approved for use with these species. We report the effects of three low rates of subsurface drip irrigation on seed yield of E. heracleoides and E. umbellatum, and how these seed yield responses to irrigation are affected by precipitation. Optimum irrigation for each species was based on the amount of irrigation and seasonal precipitation during each year of production. Seed yield response of E. umbellatum to irrigation has been reported for the earlier years of this trial (Shock et al., 2015). Because seed yield can vary between years due to harsh weather, differences in pollination, and many other factors, we report also the effects of the low rates of subsurface drip irrigation on the relative seed yield calculated as the percentage of the yield of the highest yielding treatment for each species for each year.

Irrigation Requirements for Seed Production of Five Lomatium Species in a Semiarid Environment

Lomatium species are important botanical components in the rangelands of the Intermountain West. Relatively little is known about the cultural practices necessary to produce Lomatium seed for use in rangeland restoration activities. The seed yield response to four biweekly irrigations applying either 0, 1, or 2 inches of water (total of 0, 4, or 8 inches/season) was evaluated for four Lomatium species over multiple years starting in 2007. Over seven seed production seasons, Lomatium dissectum (fernleaf biscuitroot) seed yield was maximized by 5-6 inches of water applied per season in cooler, wetter years and by 8 inches of water applied per season in warmer, drier years. Over nine seed production seasons, L. grayi (Gray’s biscuitroot) seed yield was maximized by 0-5 inches of water applied per season in cooler, wetter years and by 5-8 inches of water applied per season in warmer, drier years. Over nine seed production seasons, L. triternatum (nineleaf biscuitroot) seed yield was maximized by 4-8 inches of water applied per season in cooler, wetter years and by 8 inches of water applied per season in warmer, drier years. Over four seed production seasons, L. nudicaule (barestem biscuitroot) seed yield did not respond to irrigation. In two seed production seasons, seed yield of L. suksdorfii (Suksdorf’s desertparsley) responded to irrigation in one year.