Use of Time Domain Reflectometry can reduce water use and nutrient leaching in container nursery production
Ristvey, A.G.; Lea Cox, J.D.; Ross, D.S.
HortScience 38(5): 671-672
Various state and federal nutrient management regulations are ensuring a re-evaluation of water and nutrient application efficiency, particularly when plants are grown in intensive, out-of-ground container-nursery and greenhouse operations. The quantity and quality of water used by intensive agriculture is a topic of national interest, as clean water is a critical requirement that helps sustain natural and managed terrestrial and aquatic ecosystems. The majority of container nursery and greenhouse operations in the U.S. are irrigated by overhead irrigation systems. Many container production systems have low irrigation water interception efficiencies, since containers are large, and plants need to be spaced to reduce the effects of canopy interaction. Water that either falls between containers, or leaches from the container, may contribute to nutrient runoff, particularly when soluble fertilizers are used. To increase water application efficiency, irrigation scheduling also needs to be based on a precise technology that can integrate diurnal plant water use, rather than using subjective 'timed' irrigation events. Time Domain Reflectometry (TDR) has been shown to precisely schedule water applications to various soilless substrates under experimental conditions. In 2002, this technology was integrated into a large-scale nursery research site at the Wye Research and Education Center in Maryland. The research site consists of two 560 m2 production houses with eight replicated blocks per house. The surface of each house was lined with two continuous layers of 6-mL polyethylene sandwiched between two layers of groundcover fabric, so that all irrigation water, rainfall and the subsequent leachate from plant containers can be captured. Overhead sprinklers irrigated half of the blocks; the other half were irrigated by pressure-compensated drip stakes, each system delivering approximately 15 mL of water per minute into each plant container. All water applications were measured by calibrated flowmeters. Water applications, rainfall events, N and P applications, plant N and P uptake, and N and orthophosphate leaching data were continuously quantified from May through November in this system, with irrigation scheduling for eight split-plots of Rhododendron cv. azalea and Ilex cornuta being entirely controlled by TDR compared to the timed cyclic daily irrigation event. Increasing irrigation interception efficiency with drip systems reduced the total amount of nitrogen and orthophosphate leached from containers. The total nutrient recovery in the leachate was higher for overhead irrigation for both species, reflecting the lower interception efficiency as compared to drip. Time-domain controlled plots had a significantly lower total water use compared to timed cyclic events for both irrigation systems and plant species. No significant differences in plant dry mass between treatments were noted. Thus by increasing interception efficiency and reducing overall water applications, we can reduce the total amount of nutrient runoff from container-production systems, without a loss in productivity.