Applying only the amount of water needed by a plant, when it needs it, is a simple concept that can conserve water and reduce runoff. Simple, that is, when managing a single crop that covers an extensive area under several irrigation zones. Container production nurseries grow a large number of plants and each irrigation zone usually has a diverse grouping of taxa in various stages of development. In 1989, a nursery crop project at Oregon State University began to investigate irrigation scheduling for container-grown woody landscape plants. Crop coefficients (kc), used to adjust irrigation to specific production practices and crop characteristics, vary greatly for woody landscape plants. Woody plant kc values range from <1.0 to >5.0 during the production cycle. Plant taxa, growth stage, spacing, and pruning significantly influence kc of container-grown plants. Ilex crenata `Green Island' showed a reduction in water use (40%) immediately after pruning, but had similar kc values 60 days later. Grouping plants with similar kc values under the same irrigation zone is a very difficult task for a production nursery. It might be more practical to schedule irrigation for daily evapotranspiration, avoid placing new plantings next to mature crops, and only separate-out plants with very high or very low crop water requirements.
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