Modeling growth of Matthiola incana in response to saline wastewaters differing in nitrogen level

The capture and reuse of nutrient-rich greenhouse effluents may be an environmentally sound option for floriculture production, which would conserve fresh water resources and reduce off-site pollution of surface and groundwaters. This study was initiated in 24 outdoor lysimeters to determine effects of salinity and varying concentrations of nitrogen on the growth, yield, and ion relations of stock [Matthiola incana (L.) R. Br.] cultivar Cheerful White. The experiment was a 4 x 4 factorial, partially replicated design with four irrigation water salinities (2, 5, 8, and 11 dS.m(-1)) and four nitrate concentrations (2.5,3.6, 5.4, and 7.1 mmol.L-1; N = 35, 50, 75, and 100 ppm). Ammonium nitrogen was included in the nutrient solutions. Stem lengths were measured three times weekly. Measurements at final harvest were stem and inflorescence lengths, stem and floret diameters, number of axillary buds and florets, and shoot and root fresh weights. Time course of stem elongation was quantified as a function of thermal time with a phasic growth model. Salinity significantly delayed initiation of the exponential growth phase, shortened its duration, and reduced the rate of plant development. The overall effect was to delay time to harvest of marketable stems. Although length of the flowering stems decreased with increasing salinity, marketable stems (approximate to 60 cm) were produced in all treatments. Mineral ion relations in the plant tissues were influenced significantly, but independently, by both salinity and nitrogen. Leaf sodium, magnesium, and chlorine concentrations increased with increasing salinity; calcium and potassium decreased. In response to increasing external nitrogen, both potassium and chlorine decreased; sodium increased, whereas calcium and magnesium were unaffected. We conclude that in closed-loop irrigation systems, the nitrogen requirements for stock are low and that growers could minimize costs and limit off-site pollution by reducing nitrogen inputs.