Importance of vanadium and nutrient ionic ratios on the development of hydroponically grown cuphea

Cuphea (Cuphea viscosissima × C. lanceolata 'PSR 23') seed contains oils that have industrial application. However, little is known regarding cuphea's optimal mineral nutritional requirements or responses to inhibiting elements. Oil seed crops often need additional phosphorus (P) to achieve optimal economic yield. Vanadium (V), a commonly occurring soil constituent, interferes with plant P uptake and earlier work showed that V is a factor in lipid metabolism. Hydroponic culture was used to evaluate the relative effect of V on the development of cuphea. Relative root length, root surface area, root weight, and aerial dry weights decreased exponentially as the V concentration increased from 0 to 153 μM. In contrast to field observations of other crops, additions of MgSO4 to increase the Mg:(Mg+Ca) ratio further decreased plant growth by as much 50% at V concentrations greater than 31 μM. Root length was decreased by about 50% of the control when the plant was grown in 153 μM V and relative root area and dry weight were decreased by ≥75%. Increases in V concentration sharply reduced secondary and higher order lateral branching. Reduction in root growth was accompanied by a general chlorotic appearance. The results suggest that readily available V in field situations will result in poor root growth and crop performance. Also, the interaction of V and MgSO4, common in soils in the region, will lead to further reductions in yields in the field.