Physiological Characteristics of Nitrate Uptake by Different Catch Crop Species

The pollution of aquifers by nitrate is aggravated by farming practices that leave the ground bare during winter. Establishment of catch crops during this time could be suitable farming strategy to decrease nitrate loss from the soil. Only a few studies are available on the physiology of nitrate uptake by these species. Experiments were conducted on Lolium perenne, Secale cereale, Trifolium incarnatum, Trifolirim alexendrnum, Phacelia tanacetifolia, Brassica rapa, Brassica napus, Sinapsis alba and Raphanus sativus grown in hydroponic conditions, in order to investigate the physiological basis of the NO3- uptake system when plants are grown with optimum ocniditons of light, temperature and nutrient availability. Maximum uptake rate (Vmax) and affinity (Michaelis constant:Km) of the root NO3- uptake system were quantified from measurement of NO3- depletion from the medium. Results showed very marked differences among species, with Km values going from 5/1+-0.6 (Trifiloum incanatum) to 36.4 +-2.0 (Lolium perenne) and maximal velocity (umol/h/g) of root fresh weight) at 25 C ranging from 9.8+-0.6 (Trifloium incarnatum) to 35+-2.0 (Brassica napus). There was a strong correlation between shoot/root ration and V max, suggesting different ecological strategies from NO3- uptake from the soil solution.