The 2011 ASHS Annual Conference

Container nursery, field nursery and greenhouse operations are intensively managed with regard to nutrient and irrigation inputs throughout the United States. This leads to the potential for high levels of nutrient (greenhouse and container) and sediment (container and field) runoff, if proper nutrient application and abatement practices are not followed.  Understanding the complexities of nutrient and water application, uptake, and loss mechanisms from these types of operations can be difficult for both growers and researchers alike.  Models were developed using the program Stella, which uses a ‘systems thinking’ approach.  Separate models were developed for greenhouse, container-nursery and field-nursery operations, since there are specific production variables and management practices associated with each type of production.  Multiple nutrient and irrigation variables were incorporated into the models.  Models were calibrated and validated with independent peer-reviewed research data.  Validation results for all three models showed consistent agreement between model outputs and published results, increasing confidence that models accurately processed input data.  The validated models were then used to run a number of what-if scenarios, based on a database of commercial water and nutrient management practices, gathered from 48 nursery and greenhouse operations in Maryland. Results of the what-if scenarios highlighted model sensitivities, and allowed for the testing of multiple hypotheses.  Factors such as the N:P₂O₅ ratio of fertilizer, fertilizer rate, interception efficiency, days irrigated per week, crop coefficients, and buffer width were analyzed under a variety of scenarios for each of the three models.  For example, interception efficiency is known to decrease with increased spacing.  In the container model, when 6 L containers were spaced 23 cm between centers (container tight), the models predicted 23.4 L of unintercepted water per container compared to 350.3 L of unintercepted water per container at 46 cm between centers, over the course of a 40 week growing season.  For the greenhouse model, it was found that by reducing constant fertigation from 200 mg/L to 40 mg/L N leaching was reduced from 1.94 g to .05 g per plant, without reducing plant nitrogen uptake. This research provides growers and researchers with tools to assess and understand the cultural and environmental impact of current practices, and predict the impact of improving those practices.  Our results provide a detailed analysis of current water and nutrient management practices, and adds significantly to our understanding of various operational practices in nursery and greenhouse operations, both in Maryland and throughout the United States.