Daily Patterns under the Life Cycle of a Maize Crop

Together with photosynthesis, transpiration and respiration, the daily uptake of NO3−, NH4+, H2PO4−, K+, Ca2+, Mg2+, SO42−, the root respiration, root volume increase and root excretions have been studied by daily measurements during the growth period of whole maize plants (Zea mays L. cv. INRA F7 × F2) raised until complete maturity on nutrient solution. The uptake patterns show a maximum absorption of NO3−, K+ and Ca2+ during the vegetative growth phase. The absorption of these ions declines during maturation while that of H2PO4− reaches a maximum. Root respiration and particularly the uptake of NO3− and K+ are well correlated with the rate of root growth. Root excretion is more notable in young plants than in the old. It represents less than 0.2% of the net assimilation of adult plants.