7 Del. Admin. Code § 7103-28.0
Current through Register Vol. 28, No. 3, September 1, 2024
Section 7103-28.0 - Crop-Soil Management and Scheduling28.1 The cropping system and soil hydraulic properties largely determine when and how much wastewater may be applied. Crops vary in their consumptive use of water (evapotranspiration), water tolerance for wet conditions and nutrient requirements. Different crops also require various degrees of management intensity and diversity of equipment and have varying potential economic returns for reducing the costs of the land treatment system. Forests and forage crops are attractive for wastewater treatment because of relatively low management requirements compared to row crops. Further, constant vegetative cover by trees or grasses promotes high infiltration and evapotranspiration and reduces potential for erosion and runoff. Although there may be more potential economic return from row crops or a diversity of crops rather than just trees or forages, the required intensity of management and the farm equipment requirements increase with row crops. Markets must also be considered when selecting the vegetation.28.2 Whether the crop is trees, forage, or row crops, all have requirements for site preparation, planting, crop maintenance, weed and pest management, harvesting, and sale or disposal of harvested material. Wastewater application will not be possible during certain periods because of required tasks, e.g. cutting and baling hay, or restrictions such as the minimum period between application and harvesting. Wastewater application scheduling must mesh with the crop management scheduling.28.3 Wastewater application and schedules and any supplemental fertilization must be matched to the crop's nutrient needs. Application of nutrients during non-growing periods can be accomplished if the form of nutrient applied is primarily one that is stored and not available for movement in percolating water. For instance, irrigation of nitrogen principally in the organic and ammonia forms results in storage on site. Whe nitrification occurs, presumably due to warmer soil temperatures and microbial activity, plants will also be actively taking up nitrate and/or denitrification will occur.28.4 Fertilizer recommendations for P2O5 and K2 O should be regularly determined by soil tests. The University of Delaware College of Agriculture Soil Testing Laboratory, Department of Plant Science, routinely runs soil tests. Fertilizer N recommendations are based on the crop being grown with allowance for residual N from the previous crop in some cases. Consequently, fertilizer recommendations on their soil test reports will always indicate that N fertilization is needed. Ignore this recommendation and apply wastewater based on design loading rates. Also, the P2O5 recommendation may need adjustment based on the design loading rate for the particular soil's P adsorption capacity and chosen site life.28.5 Fewer data are available on growth response to wastewater fertilization of forests. Infiltration rates are normally high for forest soils, but the uptake of nutrients is normally lower for trees than for forages or row crops. Forestry specialists should be consulted for managing forest land treatment sites because there is relatively little information available in publications on forest management compared to the Delaware Agricultural Extension Service's bulletins on forage and row-crop management.28.6 Irrigation scheduling must also take into consideration the soil moisture conditions and adjust scheduling or amount of application when necessary to prevent surface runoff or ponding and to allow adequate reaeration of the soil's A horizon for proper crop growth and wastewater treatment. Soil moisture measurements or tensiometers may be helpful in making irrigation decisions for sensitive crops.28.7 Regardless of what crop is grown, land treatment systems must be managed in accordance with good agricultural practice. Sites receiving a high hydraulic loading will require careful management not common to normal farm operations due to the constant wet soils and need to control equipment access. It is advisable to hire a capable manager and require the manager to be familiar with and operate the system in accordance with a detailed "Operations and Management" manual. Adequate safety allowances should be built into the design to allow for a range of expected management capabilities as well as variability in crop yield and uncontrollable variables such as weather. The system should be designed using realistic average crop yields and nutrient uptake, not the maximum which may occur only one year in ten. If the crop removal of nutrients is not as much as designed for, then there is potential for environmental degradation. To assure nutrient removal from the site, marketing or utilization of harvested crops should be planned in advance. Timely crop harvest and removal from the site is necessary to maintain design nutrient balances.7 Del. Admin. Code § 7103-28.0