Effects of solution pH, temperature, nitrate/ammonium ratios, and inhibitors on ammonium and nitrate uptake by Arabica coffee in short-term solution culture
1998
Vaast, P. | Zasoski, R.J. | Bledsoe, C.S.
Solution pH, temperature, nitrate (NO3(-))/ammonium (NH4(+)) ratios, and inhibitors effects on the NO3(-) and NH4(+) uptake rates of coffee (Coffea arabica L.) roots were investigated in short-term solution culture. At intermediate pH values (4.25 to 5.75) typical of coffee soils, NH4(+) and NO3(-) uptake rates were similar and nearly independent of pH. Nitrate uptake varied more with temperature than did ammonium. Nitrate uptake increased from 0.05 to 1.01 micromoles g-1 FW h-1 between 4 and 16 degrees C, and increased three-fold between 16 to 22 degrees C. Between 4 to 22 degrees C, NH4(+) uptake rate increased more gradually from 1.00 to 3.25 micromoles g-1 FW h-1. In the 22-40 degrees C temperature range, NH4(+) and NO3(-) uptake rates were similar (averaging 3.65 and 3.56 micromoles g-1 FW h-1, respectively). At concentrations ranging from 0.5 to 3 mM, NO3(-) did not influence NH4(+) uptake rate. However, NO3(-) uptake was significantly reduced when NH4(+) was present at 3 mM concentration. Most importantly, total uptake NO3(-) + NH4(+)) at any NO3-/NH4(+) ratio was higher than that of plants fed solely with either NH4(+) or NO3(-). Anaerobic conditions reduced NO3(-) and NH4(+) uptake rate by 50 and 30%, respectively, whereas dinitrophenol almost completely inhibited both NH4(+) and NO3(-) uptake. These results suggest that Arabica coffee is well adapted to acidic soil conditions and can utilize the seasonally prevalent forms of inorganic N. These observations can help optimizing coffee N nutrition by recommending cultural practices maintaining roots in the temperature range optimum for both NH4(+) and NO3(-) uptake, and by advising N fertilization resulting in a balanced soil inorganic N availability.
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