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Temporal changes in nitrate status of orchard soils with varying management practices

Koehn, A.C., F.J. Peryea, D. Neilsen and E.J. Hogue . 2002. Communications in Soil Science and Plant Analysis 33:3621-3634

Abstract

Two anion exchange membrane systems (Plant Root Simulator (PRS)™ probe and Dynambio nitrate selective anion exchange membranes) were evaluated as tools to estimate temporal changes in nitrate nitrogen (NO3-N) in the topsoils of four central Washington, USA apple orchards. Various management practices and different growing conditions were studied in the four orchards. Higher NO3-N was associated with increasing amounts of fertigated N, larger irrigation events, and surface application of alfalfa hay mulch and/or dairy compost. Nitrate nitrogen adsorbed by the membranes was lower when actively growing roots were present in the vicinity of the membranes, suggesting that uptake of NO3-N by apple tree and cover crop roots decreased the concentration of NO3-N in the soil solution. Thus, in the presence of plant roots, the estimate of the amount of phytoavailable NO3-N in the soil provided by the anion exchange membranes may be ambiguous. On the other hand, if roots can be excluded from the immediate vicinity of the membranes, the NO3-N adsorbed by the membranes may estimate the phytoavailability of NO3-N in the soil solution. Because anion exchange membranes provide information about the amount of NO3-N remaining in the soil after plant roots have met their demand, the membranes may be useful for estimating relative potential for NO3-N leaching. In summary, sequential use of anion exchange membranes appears to provide valuable information about temporal changes in the supply of soil NO3-N with various orchard management practices.