Growth and nutrition of pansy as influenced by N-form ratio and temperature

Pansy (Viola x wittrockiana Gams.) producers often observe nutrient disorders among plants grown during warm periods (> 18 degrees C) of the growing season. These disorders typically are not seen when production temperatures are optimal (< or = 18 degrees C) even though fertility regimes may remain the same. Our objectives were to assess the effects of temperature and nitrogen (N) fertility on growth and nutrition of pansy. Pansies cultivar 'Crown White' were grown until lateral branches had open flowers. Treatments consisted of two temperatures (12 and 22 degrees C) and three NO3(-):NH4(+) molar % ratios (100:0, 62:38, and 25:75) with a total concentration of 100 mg N L(-1). A modified Hoagland's solution was used with NO3(-)-N supplied as Ca(NO3)2, and KNO3 and with NH4(+)-N as (NH4)2SO4. Cumulative nutrient absorption and foliar nutrient content were determined when plant lateral branches flowered. Root and shoot growth were limited when NH4(+) was present in solutions at high ambient air temperature (22 degrees C), but not at low temperature (12 degrees C). Individual absorption and accumulation of plant nutrients varied with N regimes and temperatures. Overall, pansies absorbed more total N, NH4(+), NO3(-), calcium (Ca), potassium (K), magnesium (Mg), phosphorus (P) zinc (Zn), and less iron (Fe) and manganese (Mn) at 12 degrees C than at 22 degrees C. In addition, absorption of NO3(-) by pansy was negligible if any NH4(+) was present in solutions at 22 degrees C. Results suggest that pansy growers should adjust fertility programs according to production temperatures to avoid possible nutritional disorders and maximize plant growth. If maximum growth is to be obtained in warm temperatures, the use of NH4(+)-containing fertilizers should be reduced or eliminated. However, the choice of NO3(-):NH4(+) ratio for nutrition may be less important under cool growing conditions.