WATER & NUTRIENT MANAGEMENT PRACTICES

Introduction

The Federal Clean Water Act of 1972 requires that all sectors of agriculture develop effective procedures to prevent pollution of our nation’s water resources. Container nurseries, though considered non-point source polluters, are no exception. Nutrient management plans formulated for a container nursery must consider both water and nutrient applications, because container-grown plants require irrigation on a daily basis during the majority of the production cycle. Thus, nutrients can leach from containers before being used by plants. Watering too often or excessively during each irrigation event results in nutrient loss from the container via leaching.  Reapplication of fertilizer is often necessary to maintain desired plant growth rate, potentially increasing nutrient loading to the environment.

In the absence of specific state legislation providing guidance for developing a nutrient management plan, container nurseries are advised to implement the best management practices outlined in this manual.  Documentation that a nursery follows these practices will help provide strong evidence that the nursery is minimizing the amount of contaminants (nutrients, pesticides, and sediments) entering surface and groundwater. Furthermore, collecting date to document the effectiveness of these implemented BMPs could be valuable in exonerating a nursery if specific environmental problems are attributed to the nursery.

Overview of the Water and Nutrient Management

Planning Process

The factors that need to be considered when developing a nutrient management plan for a container nursery are given in Figure 43. Attention should focus on four main BMPs:

Factors to Consider

Site Evaluation

Collection Structures

When collection structures are used, the goal is to capture the runoff and recycle or treat the water before it is released from the property. Additional provisions should be made for stormwater runoff, if the collection structures are also used for this purpose. Determine the storm event magnitude you would like to manage (25, 50, 100 year storm, etc.) and consult with a qualified engineer and the Soil Conservation Service to design management structures.

Vegetative Zones

Grass or tree and wetland vegetative buffer zones are an alternative to collection structures for producers not capturing and recycling water. Vegetative zones facilitate reduction of sediment, pesticide, and nutrient loads leaving the property in runoff. Containment structures installed before the vegetative zones slow the flow of water and trap soil or substrate particles extending the life and efficacy of the vegetative zones. Some nutrient reduction of nitrogen (by denitrification) and phosphorus (by adsorption) may also occur in the containment structure (see section on Runoff Water Management).

Irrigation Management

The overriding objective is to design and operate an irrigation system that will supply adequate and uniform application of water to the plants with minimal nutrient leaching from containers and minimal runoff from the production area.

Plant Water Requirements

Plants are grouped according to water requirement (Table 2) (e.g. species, container size, and plant age) to maximize water use efficiency (see section on Irrigation Application Amount).

Minimal distances are maintained between overhead-irrigated containers without sacrificing plant quality (see section on Overhead Irrigation System Design).

Irrigation Systems

Existing irrigation system is checked bi-annually to determine if the system is delivering water uniformly (see sections on Overhead and Microirrigation System Design).

Irrigation is applied only when needed for just long enough to uniformly wet the container substrate with minimal leaching (see section on Irrigation Application Amount).

Cyclic irrigation is used to reduce leaching and runoff (see section on Methods of Application).

Substrates

Substrate Selection and Management

Select container substrates that are best adapted to the plants species and management (see section on Container Substrates). Avoid substrates that are too porous and require frequent watering (see section on Container Substrate Physical Properties). Methodology for determining substrate physical properties is given in Appendix B.

Plant Nutrient Requirements

Fertilizer Type and Rate

The general principle is to apply the least amount of fertilizer to maximize plant growth, but in a way that minimizes nutrient leaching. This can be accomplished with different management strategies using dry granular fertilizer or solution fertilizer applied at various rates, depending on the intensity of management (see sections on Pre- and Post Plant Fertilizer Applications and Controlled-Release Fertilizer).

Plant Nutrient Requirements and Application

Fertilizer applications should be made at recommended rates based upon plant requirement (species), container size, plant age, growth rate, and the time of year (see sections on Pre- and Post Plant Fertilizer Applications and Controlled-Release Fertilizer).

Fertilizer applied through the overhead irrigation system should be properly managed, so it does not greatly increase the chance of significant nutrient runoff from the nursery (see section on Fertilizer in Irrigation Water).

Monitoring Substrate Nutrients

Nutrient levels in container substrates should be monitored to assure levels are appropriate for desired growth. This should be performed on representative plants of similar size and with similar fertilizer and irrigation programs (see section on Monitoring Container Substrate Nutrient Status).

Fertigation application rates and reapplication of granular fertilizer should be based on monitoring the electrical conductivity (EC) of substrate solution. EC should be checked at least monthly during plant production (see section on Monitoring Container Substrate Nutrient Status).

Record of Fertilizer Application

An accurate record should be made of fertilizers applied for each plant type (high, medium or low nutrient requirement) and container size. This data should be recorded in such a way that total nitrogen and phosphorus applied for the nursery could be calculated on an area basis or on a crop basis (see section on Record of Fertilizer Application). Another approach would be to keep fertilizer receipts to calculate per acre application amounts of N and P for the nursery. See Appendix C for examples. Fertilizers can be applied through the irrigation system or directly on the substrate surface (granular or controlled-release. Fertilizer type, plant species, container size, and time of year are factors affecting fertilizer application amount.

Developing a Water and Nutrient Management Plan

The management strategies outlined above provide the components of a Water and Nutrient Management Plan. Implementation and documentation of these suggested nutrient and irrigation management practices such as fertilization records, monitoring EC of substrates, and determining irrigation application uniformities demonstrates that you are applying water and nutrients in an environmentally conscious way. A checklist (Table 10) is given to help evaluate your practices and identify risks.

Table 10. A checklist of practices used to develop a nutrient management plan.