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Two coarsely ground air-dried municipal sewage sludges and a garbage compost were mixed with Hartsells fsl (limed to pH 5.5) rates of 15, 75, or 300 g/3 kg of soil in two greenhouse pot experiments. Fine ZnSO₄ and Na₂Cr₂O₇ were each mixed with soil limed to pH 5.5 to 7.0 at rates up to 1,400 ppm of Zn and 320 ppm of Cr, equivalent to rates applied in the organic wastes. Three successive crops of corn (Zea mays L.) were planted 0, 7, and 18 months after waste application. Corn forage yields were increased only in Crops 1 and 3 by compost applications but were not affected by sludge applications. Concentrations of Zn in the corn forage increased with application rate and Zn content of the three waste products. In contrast, Cr concentrations in the corn were not affected by the 0.05% to 1.36% Cr in the wastes. Concentrations of both Zn and Cr in the corn forage were much higher from ZnSO₄ and Na₂Cr₂O₇ from each waste at similar Zn and Cr rates and soil pH. Levels of 0.5N HCl-extractable Zn and Cr in the soil after each harvest increased with application rate of Zn and Cr in each organic waste and inorganic salt, but were not proportional to plant concentrations. Trivalent Cr as Cr₂(SO₄)₃ was less toxic to corn than hexavalent Cr as Na₂Cr₂O₇ at a rate of 80 ppm of Cr, while both sources were very toxic at 320 ppm. Toxicity resulted from ZnSO₄ in pH 5.5 soil at 240 ppm Zn and at 960 ppm in soil above pH 6.5. Results of these experiments suggest that Zn and Cr contained in municipal wastes applied at high rates are not toxic to corn even after relatively long periods in the soil. Reduced plant uptake of these heavy metals in organic waste was not due entirely to their liming effect on the soil.

Absorption of Zn by 14-day-old intact rice seedlings was studied in short-term uptake experiments. Severe retardation of Zn absorption by various metabolic inhibitors indicated that an active process prevails at Zn concentrations often found in soil solutions. Several cultivars all showed similar sensitivity to the metabolic inhibitor 2,4-dinitrophenol (DPN). At concentrations of 10−4 M, both FeCl2 and MnCl2 depressed Zn uptake in roots and translocation to shoots; uptake was depressed to a lesser extent with Ca. Although Mg reduced uptake by the roots, translocation to the shoots was enhanced. These results suggest that high solution concentrations of reduced Fe and Mn which develop in paddy culture may be related to Zn nutrition. This information could assist in predicting Zn deficiency and may explain correction of Zn deficiency by draining flooded rice fields.

Soil applications of inorganic Fe sources are generally not effective for crops unless rather high rates are applied. Since previous results had indicated that these sources may be effective if applied at lower rates with fluid polyphosphate fertilizers, several greenhouse pot tests were conducted. Dry matter production and Fe uptake by grain sorghum (Sorghum bicolor) were higher with FeEDDHA than with FeSO₄ or Fe₂₍SO₄)₃ applied to Epping sil (pH 7.5), a calcareous soil low in available Fe. There was very little crop response to either inorganic Fe source applied alone to the soil at rates up to 24 ppm Fe. However, both sources were somewhat effective when applied with fluid polyphosphate fertilizers at the same rates. Seed and foliar spray applications were not as effective as soil application, probably because the rate of Fe was limited by the application method. Without applied Zn, crop response to FeEDDHA was limited. However, Zn uptake by sorghum decreased while forage yields increased with FeEDDHA application rate, even though ZnSO₄ was also applied to the soil. Evidence for a marked Fe-Zn interaction in sorghum was shown on this soil. Application of ZnSO₄ to the no-Fe check treatment reduced growth and Fe uptake, while high Fe applications reduced Zn uptake in the presence or absence of applied Zn.

Zinc deficiency in rice (Oryza sativa L.) has only recently been diagnosed. Although most Zn studies have been conducted on flooded rice, comparative data concerning the availability of Zn under upland and flooded soil conditions is needed. Therefore, rice (var. ‘Bluebelle’) was grown hi greenhouse pots on flooded and moist, limed Crowley sil (pH 7.5). Phosphorus, as concentrated superphosphate, was applied at rates of 20 and 200 ppm and Zn as ZnSO₄, was applied at rates of 1, 4, and 16 ppm. Dry matter production and P uptake of immature plants were doubled and uptake of Zn was up to five times as great when the plants were grown on flooded rather than moist soil. The Zn concentration in the tissue decreased at the high P rate on moist but not on flooded soil. The percentage recovery of fertilizer Zn by the crop was greater from flooded than moist soil, especially at the high P rate. Mixed and surface applications of Zn were comparable for flooded rice, whereas middepth placement (8 cm below soil surface) was less effective. Both surface and middepth placements were less effective than mixing under nonflooded soil conditions. Results of laboratory studies indicated that the mobility of Zn applied as ZnSO₄ was comparable in flooded and moist soil. The amount of DTPA-extractable Zn tended to be higher in moist than in flooded soil. This suggests that DTPA may not provide a reliable measure of Zn availability in flooded soils and that differences in Zn uptake may be related to root distribution or some other physiological or morphological characteristic of rice roots growing in moist or flooded soil.

Fertilizers varying in level of H₂O-soluble Zn were prepared by combining fine ZnO and ZnSO₄ in various proportions and pressure-granulating the powders with ammonium nitrate, monoammonium phosphate, or ammonium polyphosphate. Forage yields and uptake of Zn by corn (Zea mays L.) grown on a P- and Zn-deficient soil in the greenhouse increased with the level of H₂O-soluble Zn in these macronutrient fertilizers. Additional crop response was slight to fertilizers with levels of H₂O-soluble Zn in excess of about 50% but this varied, depending upon the macronutrient carriers. However, the amounts of Zn extracted after cropping from untreated soils and soils initially receiving 12 mg of Zn per 3 kg of soil in a highly H₂O-soluble form were comparable. In a second experiment differential response of several corn hybrids to amount of P and Zn and level of Zn solubility in the fertilizers suggests that the test variety might influence the interpretation of the results from fertilizer evaluation studies. No relationship was found between P/Zn ratios in the corn forage and the seed. The P/Zn ratios in corn forage were not related to the response of corn to applied Zn.

Dry matter production and uptake of Zn, N, and P by corn grown in greenhouse pots were higher with (NH₄)₂SO₄ than with anhydrous NH₃ or CO(NH₂)₂, whether ZnSO₄ was mixed, spotplaced, or not applied. These results are largely explained by the lower soil pH associated with application of (NH₄)₂SO₄ and hence, the increased availability of indigenous and applied Zn. Yields were lower when Zn was mixed, but higher when Zn was omitted or spot-placed 4 weeks prior, as compared to treatment just prior to planting. In general, Zn and N uptake varied directly with yield and inversely with P uptake, except where growth was extremely poor due to severe Zn deficiency.

Zinc oxide, ZnSO₄, and ZnS were tested as sources of Zn at rates of 1, 2, and 4 ppm Zn for two successive crops of corn (Zea mays) grown on Nolichucky sandy clay loam (pH 7.3). Each source was mixed throughout the soil as finely ground material, incorporated into granules of ammonium nitrate (AN) or ammonium polyphosphate (APP) by pressure granulation, and into granules of concentrated superphosphate (CSP) during the granulation stage of the manufacturing process. When mixed with the soil ZnO and ZnSO₄ were more effective than when incorporated with a macronutrient carrier. Both ZnO and ZnSO₄ were markedly superior to ZnS. Ammonium nitrate and APP were comparable carriers when ZnSO₄ was the source, but APP was superior to AN when ZnO was used. A higher concentration of Zn in the CSP granules resulted in poorer response to this carrier. Zinc oxide was pressure granulated with CSP, AN, APP, or Nolichucky soil to contain 0.5, 2.0, or 8.0% Zn. Soil granules and CSP were applied at 1, 2, and 4 ppm Zn while AN and APP were applied at 2 ppm only. Forage yields and Zn uptake varied inversely with concentration of Zn in all carriers.

Movement of Zn in Hartsells fine sandy loam (pH 5.2) from granules containing 2% Zn as ⁶⁵Zn labeled ZnSO₄ decreased in the order: ammonium nitrate (AN) > soil (no carrier) = concentrated superphosphate (CSP) > monoammonium phosphate (MAP) = triammonium pyrophosphate (TPP). In limed soil (pH 7.1) Zn movement was less from MAP than from all other carriers, and Zn movement from each carrier was less than that in acid soil. Zinc also moved further from MAP than TPP in other soil systems below pH 6.0, the same between pH 6.0 and 6.8, and less above this range. Most Zn movement from P carriers occurred during the first week, except in extremely acid soil. Carrier-Zn reactions affected the amount of Zn which moved out of the fertilizer granules, but soil-Zn reactions were also important in affecting Zn movement from the granule site. The recovery by various chemical extractants of Zn applied in granules of soil and in all macro-nutrient carriers to acid soils was similar. The amount of Zn recovered by 2N MgCl₂ from limed soil less than 0.5 cm from the granule varied with carrier after 1 week, but was similar for all carriers after 8 weeks. Uptake of Zn by corn (Zea mays L.) in a greenhouse pot experiment was greater from AN, but no clear relationship was evident with the P carriers.

Movement of Mn in acid Hartsells fsl (pH 5.1) from fertilizer granules containing 2% Mn as ⁵⁴Mn-labeled MnSO₄ was in the order: KCl = NH₄NO₃ [AN] > soil (no carrier) = concentrated superphosphate [CSP] = NH₄H₂PO₄ [MAP] ≫ (NH₄)₂HPO₄ [DAP] = (NH₄)₃HP₂O₇ [TPP] = ammonium polyphosphate [APP]. In limed Hartsells soil (pH 7.6) Mn movement was less from granules of all fertilizers, but the order remained the same. Movement of Mn applied in soil or MAP granules was greater in Spencer sil (pH 4.7) than in five other soils with higher pH levels. Application of Mn with MAP resulted in decreased Mn movement in all soils except Houghton muck. Little or no movement of Mn occurred when MnSO₄ was applied with TPP to any of these soils. Reduced movement may have been due to formation of reaction products of low solubility which reduced the concentration gradient of soluble Mn in the soil near the granule site. Percentage recoveries of applied Mn from the soil immediately adjacent to the granule sites by H₂O, neutral 1N NH₄OAc, and neutral 1N NH₄OAc containing 0.2% hydroquinone showed little difference for Mn applied alone or with granular AN, KCl, CSP, or MAP. However, the recoveries of Mn applied with DAP, APP, and TPP were lower, indicating lower solubility of Mn applied with these fertilizers. Recoveries of applied Mn also were less in soils with higher pH levels.

Maize and pea bean plants were grown for 2 weeks in Zn-deficient soil fertilized with varying levels of Fe and Zn. The plants were then exposed to C14O2 for 2 minutes and after harvest the ethanolsoluble photosynthate was fractionated into carbohydrates, organic acids, and amino acids. There appeared to be a general increase in the CO2 assimilation rate by maize with increasing rate of Zn; rates were slightly higher with applied Fe, at each Zn level. In contrast to maize, the rate of assimilation by pea beans was unaffected by substrate Zn and was slightly lower with application of Fe, especially in the carbohydrate fraction. Increasing rates of applied Zn had little effect on concentration of Fe and Mn in the maize or pea bean tops. However, application of Fe resulted in a depression in Zn concentration of maize. Despite the relatively high levels of Zn in the tissue of both species, there was no increase in total organic acids assimilated or any indication of gross metabolic imbalances.