Effects of lime and phosphorus on selected alluvial entisols from eastern Costa Rica. II–Forage plant responses
AbstractA glasshouse study was conducted to determine the effects of lime on native soil phosphorous availability; the availability of applied phosphorous was measured by Pangola grass (Digitaria decumbens Stent). The Grass, grown in surface and subsoils that had large amounts of residual phosphorous of low availability, responded markedly to applied phosphorous necessary for maximum yields were calculated to be 290 p.p.m. for the limed and 348 p.p.m. for the unlimed soils. In the untreated surface soils, forage growth improved with time as the grass developed more extensive root systems, but it remained extremely poor in the subsoil where phosphorous was omitted. Applied phosphorous enhanced root growth and remained available for one year after application. Forage phosphorous concentrations were low (0·03 to 0·12 per cent), even at high rates of applied phosphorous. The recovery of applied phosphorous in the forage varied from 3·4 to 14 per cent and depended on lime and phosphorous rates. Forage yields decreased as lime rates were increased, regardless of the rate of phosphorous applied. Lime had an unfavourable effect on root growth. Soil pH increased from 5·1 (untreated) to 6·6 after application of 75 p.p.m. of phosphorous and 500 p.p.m CaCO3. Forage manganese concentrations were markedly reduced in the lime soils but this did not appear to be the cause of depressed plant growth. Lime injury may have been partly overcome by substituting 50 per cent CaCO3 with MgCO3.