Identifying Optimal Fertility Rates for Sustainable Floriculture Production

During bedding plant production, fertilizer nutrients are often leached from the media and may cause environmental contamination. Fertilizer recommendations should be adjusted to meet plant requirements and maintain quality while minimizing waste. Such an approach reduces fertilizer use and enhances environmental stewardship. On the other hand, the issue of plant quality is a concern when modifying a fertility program. While dry weight provides a means of comparing plant growth, it is not the only factor that contributes to plant quality. Four quality aspects, including leaf greenness, flower count or flower dry weight, total dry weight, and consumer preference ratings were measured to identify an ideal rate for four fertilizers under typical production conditions. Catharanthus roseus ‘Salmon', Celosia argentea ‘Grow Red', and Impatiens hawkeri ‘Paradise New Red' were grown in a rate experiment using two granular and two water-soluble fertilizers: 1) Contec-DG® 15N-3.9P-9.9K at rates of 1 kg•m^-3, 2.14 kg•m^-3, and 3.57 kg•m^-3, top-dressed, and 2) Osmocote® Plus 15N-3.9P-9.9K, 3-4 month longevity at rates of 3.56 kg•m^-3, 5.33 kg•m^-3, 7.11 kg•m^-3, top-dressed; 3) Daniels® 10N-1.8P-2.5K and 4) Peters Peat Lite® 20N-4.4P-16.6K fertigated at rates of 75 mg•L^-1 N, 150 mg•L^-1 N, and 250 mg•L^-1 N. Raw data were transformed to fit a scale of 0-5 for each quality aspect to yield a total quality index. Data analyses of the quality aspects were conducted using linear regression. Significant differences between the quality indices were identified using ANOVA and LSD (α = 0.05), which allowed for determination of the minimum rate observed at which the maximum quality rating was obtainable. ‘Optimal' rates were determined to be as follows: Contec-DG®: 2.14 kg•m^-3 for C. roseus and I. hawkeri, 3.57 kg•m^-3 for C. argentea; Osmocote® Plus: 5.33 kg•m^-3 for C. roseus and C. argentea, 7.11 kg•m^-3 for I. hawkeri; Daniels®: 150 mg•L^-1 N for C. roseus and I. hawkeri, 250 mg•L^-1 N for C. argentea; Peters Peat Lite®: 150 mg•L^-1 N for C. argentea and C. roseus, 75 mg•L^-1 N for I. hawkeri. These fertility rates will be used for further comparison of the effect of the fertilizers on leachate nutrient content, tissue nutrient content, and plant quality.