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Sugarcane (a complex trispecies hybrid of Saccharum) is one of few crops which are highly responsive to applications of silicate materials. Variety ‘C.P. 63‐588’ was grown on a Pahokee muck soil (euic, hyperthermic Lithic Medisaprist) to evaluate effects of silicate sources and rates on growth of cane and sugar yield. Data were collected from the initial planting and a subsequent ratoon crop. Silicate materials were applied to 79.2 m2 field plots at the rates of 0, 5, 10, 15, and 20 metric tons/ha of TVA slag, Florida slag, and Portland cement. A factorial experiment was established in a randomized complete block design with five replications. The silicate materials were broadcast by hand and then thoroughly mixed with the soil by a disc harrow. Growth was measured as plant height, stem diameter, and number of millable stalks. Yield was determined as metric tons of cane and sugar per ha. Application of silicate materials increased plant height, stem diameter, number of millable stalks, and cane and sugar yields in both plant and ratoon crops. Addition of 15 metric tons/ha of silicate materials increased cane and sugar yields by 68 and 79% in the plant crop, and by 125 and 129% in the ratoon crop, respectively. Although there was no significant difference among the silicate materials in the plant crop, Florida slag increased growth and yield more than the other two materials in the ratoon crop. The vital role of Si in sugarcane growth was evident by increased plant size and increased tillering.

Adsorption and precipitation of Cd2+ in soil suspensions were investigated as possible factors controlling Cd2+ levels in soils. Both adsorption of Cd2+ onto soils surfaces and possibly precipitation of cadmium minerals were evident in this study. At low cadmium levels solubility relationships in soils are best described by adsorption and fit the empirical Freundlich adsorption isotherm. Based on current thermodynamic data the solid phases CdCO3 (log Ksp = −12.07) and Cd3(PO4)2 (log Ksp = −32.61) most likely limit Cd2+ activities in soils. Under alkaline conditions, Cd2+ activity decreased approximately 100‐fold for each unit increase in pH. In this study, CdCO3 precipitated in sandy soils, having low cation exchange capacity (CEC), low organic matter, and pH values >7.0.DTPA‐extractable cadmium levels in soils were highly correlated (r = 0.96) with Cd concentrations in corn (Zea mays L.) seedlings grown on soils amended with Cd solutions, sewage sludge, or Cd‐spiked sewage sludge. Increasing Cd additions to the soil increased plant Cd regardless of the form of Cd added. Addition of inorganic Cd to the soil increased the Cd concentration of corn seedlings more than equivalent Cd additions in the form of sewage sludge or Cd‐spiked sludge.

Corn (Zea mays L.) ‘Pioneer‐3932A’ was grown in the greenhouse on a loamy sand amended with cadmium, cadmium‐spiked sewage sludge, and sewage sludge. Soil pH was adjusted to approximately 5.7, 6.7, and 7.8, and phosphorus was applied at 0, 200, and 400 µg/g soil. Soil treatments were applied 0, 8, and 16 weeks prior to planting, and the plants were grown for 5 weeks.Increasing the pH of the soil amended with inorganic cadmium (CdSO4) decreased the Cd concentration of corn seedlings by approximately 67%. The Cd concentration was reduced approximately 47% for a similar increase in pH on soil amended with Cd‐spiked sludge.The Cd concentration of corn seedlings was significantly reduced by the addition of P. Increasing incubation time decreased the availability of added inorganic Cd, but increased the availability of Cd applied with sewage sludge.Increasing the amount of Cd added to the soils increased the Cd concentration of the corn seedlings regardless of the form of Cd used. Cadmium concentrations in the corn seedlings were significantly correlated with DTPA‐extractable soil Cd.Solubility measurements of Cd in the acidified soils showed undersaturation with respect to all known Cd minerals, whereas in soils above pH 7.25 the Cd solubility was limited by CdCO3 at a CO2 level of 0.003 atm or higher and showed the expected hundredfold decrease in solubility for each unit increase in pH. The minerals Cd3(PO4)2 and Cd(OH)2 are much too soluble to account for the precipitation of Cd in these soils.

The objective of this study was to evaluate the effect of natural and synthetic complexing agents on Cd2+ adsorption characteristics of metal hydroxides and silicate clay minerals. The solution pH at which 50% of the initial solution Cd2+ was adsorbed was 5.40, 7.00, 7.80, and 8.30 for Al(OH)3, Fe(OH)3, montmorillonite, and kaolinite, respectively. The presence of citrate (C6H5O73‐) depressed Cd adsorption on Al(OH)3, by approximately 25% in acidic solutions. The addition of EDTA (C10H16O8N2) depressed the Cd adsorption on both Al and Fe hydroxides, montmorillonite, and kaolinite in acidic and alkaline solutions. The water‐soluble organic fraction from sewage sludge enhanced Cd adsorption by both kaolinite and montmorillonite in alkaline solutions. The water‐soluble organic fraction from an organic soil (Terra Ceia muck) increased Cd adsorption by Fe(OH)3 only under acidic conditions.Preliminary results indicated that considerations of Cd retention by soil constituents should include not only the aqueous chemistry of Cd and the surface chemistry of the adsorbent, but also the chemistry of natural and synthetic complexing agents. The interaction of Cd and various complexing agents can play an important part in determining the fate of this metal in the soil‐water‐plant environment.

Summary An important process which affects the fate of fertilizer nitrogen (N) applied to a rice crop is crop N uptake. This uptake rate is controlled by many factors including the N-ion species and its concentration. In this study the relation between N concentration at the root surface and N uptake was characterized using Michaelis-Menten kinetics.The equation considers two parameters, Vmax and Kin, which are measures of the maximum rate of uptake and the affinity of the uptake sites for the nutrient, respectively.Uptake rates of intact rice plants growing in a continuously flowing nutrient solution system were fitted to the Michaelis-Menten model using a weighted regression analysis. For NHq-N the Km values for 4-and 9-week-old rice plants indicated a high affinity for the ammonium ions relative to concentrations reported for rice soils after fertilization. The Vmax values expressed on a unit-rootmass basis decreased with plant age, indicating a reduction in the average density of uptake sites on the root surface.The kinetics of NO3-N uptake was similar to that of NH4-N when NO3-N was the only N source. However, if NH4-N and NO3-N were present simultaneously in the solution the Vmax for the uptake of NO3-N was severely reduced, while the Km was affected very little. This inhibition appears to be noncompetitive.Fertilization of young rice plants leading to concentration of N at the root surface above approximately 900 pM will not increase crop uptake and may contribute to inefficient N recovery by the crop. The existence of NH4-N and NO3-N simultaneously at the root surface may also lead to inefficient N recovery because of reduced uptake of NO3-N.

The effects of several environmental factors on the fate of hydrazinc in aqueous systems were studied. In aqueous systems, the primary mechanism of hydrazine (N2H4) degradation appears to be a four‐electron oxidation to N2 gas by oxygen. The oxidation rate was very slow in distilled water but increased with the addition of catalysts such as Cu(II) and phosphate ions. Conditions that accelerated the formation of the hydrazyl radical, the first step in hydrazine oxidation, increased the proportion of one‐electron oxidation. This resulted in increasing the formation of ammonia as one of the degradation products. Ammonia evolution was correlated with Cu(II) and phosphate ion concentrations, as well as with temperature. Hydrazine oxidation was primarily dependent on the rate of the oxygen diffusion from the gas phase.

Sugarcane (a complex trispecies hybrid of Saccharum is one of the few agronomic crops known to be responsive to silicon. Field experiments were conducted on a Pahokee muck soil (euic, hyperthermic Lithic Medisaprist) to evaluate the effects of silicate sources and rates on the incidence of leaf freckling and chemical composition of sugarcane. Data were collected from the initial planting and the subsequent ratoon crop of variety ‘C.P. 63‐588.’ Application of silicate materials increased leaf chlorophyll and decreased leaf freckling in both crops. Application of 15 metric tons/ha of silicates increased leaf chlorophyll by 78 and 65%, and decreased leaf freckling by 46 and 41% in plant and ratoon crops, respectively. Although there was no significant difference among the silicate materials in the plant crop, Florida slag increased leaf chlorophyll and decreased leaf freckling more than TVA slag and cement in the ratoon crop. Application of silicate materials increased the levels of Si, P, Ca, and Cu, and reduced the levels of N, K, Mg, Fe, Mn, and Zn in the leaf. Florida slag increased Si and P in the leaf more than the other two materials. Silicate materials also increased soil pH, soil Si, soil P, soil Ca, and soil Mg. Florida slag and TVA slag increased soil P more than cement, whereas cement increased soil pH more than either slag. The increase in leaf P is attributed to the amount and solubility of P applied and not to any solubilization of soil P by silicates.