Molybdenum status of Texas soils : fertilization trials, anion exchange estimations, and correlation with soil chemical properties

Abstract

Fifty five surface soils were evaluated for yield response to Mo fertilization. Dry matter yields of the + Mo and no Mo treatments were significantly different on approximately 33% of the soils. Only three soils produced plant material that might cause molybdenosis in grazing animals. The relationship between relative dry matter yield and plant Mo content was better for calcareous than for noncalcareous soils. Plant available Mo was estimated by an anion exchange technique. Experimental parameters associated with the technique were investigated. The amount of Mo released from a soil varied with time of shaking, resin type, soil:water ratio and amount of resin. The best experimental conditions for estimation of plant available Mo were: Cl('-) form of the resin, 10 meq of resin, 1:4 soil:water ratio and 24 hour shaking time. A linear relationship existed between resin Mo and plant Mo content for both calcareous and noncalcareous soils. Resin Mo and plant Mo content were significantly related to relative yield for only the first harvest taken on calcareous soils. Neither property gave a good indication of the extent of yield response to Mo fertilization of noncalcareous soils. Critical Mo soil test levels were 14 and 27 ppb for noncalcareous and calcareous soils, respectively. Chloride form resin Mo and plant Mo content of subterranean clover grown on noncalcareous soils were significantly correlated with organic C, clay, DTPA-extractable Cu and DTPA-extractable Mn. Additionally, Cl('-) form resin Mo was significantly correlated with soil pH and total Mo. Total Mo was the only property measured for calcareous soils that was significantly correlated with resin Mo and plant Mo content. Regression equations were developed to correlate soil to soil changes in resin Mo and plant Mo content with soil properties. The strongest correlations were found for noncalcareous soils when DTPA-extractable Cu, DTPA-extractable Mn and Fe(,2)O(,3) were used in the model. Models containing total Mo and DTPA-extractable Fe gave the best fit when calcareous soils were considered. Calcium carbonate was the only soil property significantly correlated with the resin Mo extracted from high Mo soils from a uranium mining area.