LIMESTONE PARTICLE SIZE AND RESIDUAL LIME CONCENTRATION AFFECT PH BUFFERING IN CONTAINER SUBSTRATES

摘要

The objective was to quantify how the concentration and particle size of unreacted oresidualo limestone affected pH buffering capacity for ten commercial and nine research container substrates that varied in residual calcium carbonate equivalents (CCE) from 0.3 to 4.9 g CCE center dot L-1. The nine research substrates contained 70% peat:30% perlite (by volume) with dolomitic hydrated lime at 2.1 g center dot L-1, followed by incorporation of one of four particle size fractions [850 to 2000 m (10 to 20 US mesh), 250 to 850 m (20 to 60 US mesh), 150 to 250 m (60 to 100 US mesh), or 75 to 150 m (100 to 200 US mesh)] of a dolomitic carbonate limestone at 0, 1.5 or 3.0 g center dot L-1. Substrate-pH buffering was quantified by measuring the pH change following either (a) mineral acid drenches without plants, or (b) a greenhouse experiment where an ammonium-based (acidic) or nitrate-based (basic) fertilizer was applied to Impatiens wallerana Hook. F. Increasing residual CCE in commercial substrates was correlated with greater pH buffering following either the hydrochloric acid (HCl) drench or impatiens growth with an ammonium-based fertilizer. Research substrates with high applied lime rate (3.0 kg center dot m-3) had greater pH buffering than at 0 or 1.5 g center dot L-1. At 3 g center dot L-1, the intermediate limestone particle size fractions of 250 to 850 m and 150 to 250 (20 to 60 or 60 to 100 US mesh) provided the greatest pH-buffering with impatiens. Particle fractions finer than 150 m reacted quickly over time, whereas buffering by particles coarser than 850 m was limited because of the excessively slow reaction rate during the experimental periods. Addition of acid from either an ammonium-based fertilizer or HCl reduced residual CCE over time. Dosage with 40 meq acid from HCl per liter of substrate or titration with HCl acid to substrate-pH of 4.5 were well-correlated with pH buffering in the greenhouse trials and may be useful laboratory protocols to compare pH buffering of substrates. With nitrate fertilizer application, residual CCE did not affect buffering against increasing pH. Residual limestone is an important substrate property that should be considered for pH management in greenhouse crop production under acidic conditions.