Soil Science Society of America Journal

The Beaumont (fine, montmorillonitic, thermic Entic Pelludert) and Lake Charles (fine, montmorillonitic, thermic Typic Pelludert) soils along the Texas Gulf Coast produce only about 2 Mg rice (Oryza sativa L.) ha⁻¹ without N fertilizer, while the Nada soil (fine, montmorillonitic, thermic Typic Albaqualf) frequently produces 5 Mg ha⁻¹. In studying differences between these soils, data showed that NaCl applied to the Beaumont soil did not reduce rice yield, but equivalent amounts of KCl did. The KCl‐induced yield reduction may have been the result of NH⁺₄ entrapment in clay minerals caused by added K. Clay mineral characterization showed that the Beaumont soil fixed more NH⁺₄ than the Nada soil because the Beaumont soil was higher in soil K, high‐charge smectite [i.e., 0.76 equivalents per (Si,Al)₄O₁₀(OH)₂] and charges in the tetrahedral sites. The 8‐wk incubation of Beaumont soil in the rice root zone resulted in partial release of added Nh⁺₄ and no release of native NH⁺₄ when the Beaumont soil had been Ca saturated. The K‐saturated Beaumont soil did not release fixed Nh⁺₄ during incubation as the Ca‐saturated soil did. The Lake Charles soil showed clay and fixation characteristics similar to the Beaumont soil, while the Nada soil did not fix beyond its native level or release any upon incubation. The presence of 2:1 layer silicates in Beaumont and Lake Charles soils with x‐ray diffraction characteristics similar to smectite, and NH⁺₄ fixation characteristics similar to vermiculite, was recognized.

Manure or compost application based on N needs of corn (Zea mays L.) may result in soil accumulation of P, other ions, and salt because the manure or compost N/P ratio is usually smaller than the corn N/P uptake ratio. This study was conducted from 1992 to 1996 to evaluate effects of P‐ and N‐based manure and compost application on corn yield, N and P uptake, soil P level, and weed biomass. Composted and noncomposted beef cattle (Bos taurus) feedlot manures were applied to supply N or P needs of corn for either a 1‐ or 2‐yr period. Phosphorus‐based manure or compost treatments also received additional fertilizer N as needed. Fertilized and unfertilized checks were also included. Manure or compost application increased corn grain yield in all 4 yr as compared with the unfertilized check. Annual or biennial manure or compost application resulted in corn grain yields similar to those of the fertilizer treatment. Phosphorus‐based manure or compost application resulted in similar grain yields to those for N‐based treatments but had significantly less soil available P level after 4 yr of application. Biennial manure or compost application resulted in corn yield similar to that for annual application but increased available P in the soil. Estimated N availability was 40% for manure and 15% for compost in the first year and was 18% for manure and 8% for compost in the second year after application. Weed biomass was more influenced by nutrient availability than any weed seed introduced by manure or compost application. When application rate is based on correct N or P availability, manure and compost can produce corn grain yields that are equal to or greater than that for fertilizer application. Annual P‐based manure or compost application is the most effective method of using these resources when soil P buildup is a concern.

Scanning electron microscopy and X‐ray microanalysis were employed to characterize the morphological properties of iron coatings on rice roots at different growth stages. This information is needed for further understanding of the influence of Fe coatings on rice plant development. Rice root coatings are visible about 1 week after flooding as a brownish discoloration which thickens with age of the root. No coating was found on younger parts of major roots near their tips or on young secondary roots which are critical regions of nutrient uptake. Roots of ‘Brazos’ cultivar rice (Oryza sativa L.) plants grown in Beaumont clay soil had a relatively thin coating of FeOOH mixed with soil particles before panicle differentiation. As a rice plant approached maturity and the outermost cell wall of the root decomposed, a mixture of FeOOH and soil particles began to fill the rectangular spaces that had once been occupied by epidermal cells. Casts in open cell cavities are porous and rough on the exterior side of the root. There were many shapes of casts and they generally matched the varied shapes of the outer layer of epidermal cells of rice roots. Roots of Brazos cultivar rice grown to maturity in Katy fine sandy loam soil have completely developed polyhedral casts. Precipitation of relatively pure FeOOH on cell walls formed hollow casts with the shapes of the original cells. The models presented describe hypothetical steps in the formation of the two types of casts observed by the oxidation of Fe²⁺ by O₂ and precipitating of iron on the walls of closed and open cell cavities.

Conventional chemical extraction methods to measure labile soil P are often inadequate for detecting fine temporal‐ and spatial‐scale soil P dynamics in situ. We refined and calibrated methodology for anion‐exchange resin‐impregnated membranes (AEM), related AEM‐P to soil solution P for a high‐P‐retaining soil, and evaluated the method's viability under humid tropical field conditions. We determined: (i) AEM recyclability, (ii) AEM P sorption kinetics, (iii) the correlation between soil solution P and AEM‐P for an Andic Humitropept, and (iv) potential interference from other anions (NO⁻₃ and SO²⁻₄) on AEM P extraction. We used AEMs in a field decomposition study to evaluate plant residue and manure P release characteristics and concurrent fluxes in labile soil P. The AEM P sorption capacity was not altered significantly by repeated use. Nitrate solution concentrations in an aqueous medium of 50 and 100 mg NO₃‐N/L reduced AEM P sorption by 50 and 75%, respectively, regardless of P solution concentration; SO₄‐S at 500 and 1000 mg/L reduced AEM P sorption by ≈98%. The relationship between AEM‐P and soil solution P was curvilinear at both nonequilibrium and equilibrium soil solution P concentrations; it was essentially linear at soil solution concentrations ranging from 0 to 2 mg P/L. The AEM behaved as a dynamic exchanger rather than an infinite sink for P, particularly in the context of a low‐pH, high‐P‐retaining soil. The AEMs detected biologically relevant soil P pulses in the field decomposition study. The technique holds promise as an easy method for measuring soil P fluxes with minimal soil disturbance.

Six clearcuts ranging from 0 to 11 yr since cutting in the Piedmont of South Carolina were sampled to estimate the rate of weight loss of logging debris and to study nutrient dynamics in decomposing loblolly pine (Pinus taeda L.) slash. Density changes in wood were characterized using a negative exponential model. Decay coefficient (k) for small‐sized pieces (< 2.5‐cm diam) was 0.051 while decay coefficients for medium‐ (2.5–7.5 cm diam) and large‐ (> 7.5‐cm diam) sized pieces were 0.079 and 0.072, respectively. Overall, woody logging slash exhibited a k value of 0.072. Logging slash in contact with the ground decayed at a 50% higher rate than aerial slash. Concentrations of N and P in woody slash remained relatively constant the first few years after cutting followed by an increase. Concentrations of K, Mg, and Ca decreased in the initial stages of decomposition and then increased in the later stages. A prediction model estimated that N and P quantities in woody slash initially decrease and then increase. After 7 yr, woody slash would contain 107% of the N and 94% of the P contained in the slash initially. Potassium, magnesium, and calcium quantities show a gradual decrease with time. Woody logging slash would lose 77, 56, and 50% of the initial amounts of K, Mg, and Ca, respectively, after 7 yr. Woody logging slash acts as a nutrient sink and may be important in nutrient conservation on cutover areas.

Vegetation control (VC) and fertilization (FR) can change N availability in southern pine plantations, but the magnitude, duration, and reasons for change are not fully understood. The effects of a factorial combination of vegetation control (none vs. complete) and fertilization (none vs. 224 kg N ha⁻¹ and 56 kg P ha⁻¹) on net N mineralization and soil temperature and moisture were investigated in a 14‐yr‐old loblolly pine (Pinus taeda L.) plantation located on the Piedmont of North Carolina. Net N mineralization and soil temperature and moisture were measured monthly for 2 yr beginning in July 1998, four months after the treatments were applied. A companion aerobic laboratory incubation study of field‐moist soil was conducted at 28°C during the second year. Vegetation control increased soil temperature by 1.8°C during the growing season. Both vegetation control and fertilization increased field net N mineralization, and there was a strong positive interaction between the treatments. Net nitrification constituted 72% of net N mineralization for the combined treatment, and only 8% of net N mineralization for the other treatments. Seasonal patterns in net N mineralization were poorly correlated with soil temperature and moisture. The field and laboratory studies showed the same seasonal dynamics and magnitude of annual treatment effects on net N mineralization, suggesting other factors (e.g., labile C inputs) may be important in controlling net N mineralization.

Significant response in height, diameter, basal area, and volume growth to phosphorus (P) fertilization at time of planting lasted 17 to 20 years on a variety of sites in northern and western Florida. Ground rock phosphate and the more soluble ordinary superphosphate were equally effective P sources. Comparing the residual fertilizer P in the soil to a long‐term response of slash pine (Pinus elliottii Engelm. var elliottii) helped explain lack of differences in effectiveness of P sources. The largest long‐term slash pine responses were apparent on a poorly drained Ultisol and Inceptisol while the Spodosols were more variable in their response. There were no P responses on well‐to‐excessively‐drained Entisols.

Anion exchange membranes are commonly used to measure readily exchangeable and microbial P in soil, yet there is little information on their interactions with organic and condensed inorganic P compounds, which can interfere with interpretation of the results. We addressed this by quantifying the sorption of a range of P compounds to a commonly used anion exchange membrane (551642S, BDH‐Prolabo, VWR International, Lutterworth, UK). Sorption and recovery of orthophosphate by the membranes was complete up to 1.17 g P m⁻² The membranes also completely recovered sodium pyrophosphate, glucose 6‐phosphate, and adenosine 5′‐monophosphate, as well as significant levels (20–60%) of 2‐aminoethylphosphonic acid, sodium hexametaphosphate, and sodium phytate. Only sodium pyrophosphate, sodium hexametaphosphate, and d‐glucose 6‐phosphate were detected subsequently as molybdate‐reactive P after elution with 0.25 mol L⁻¹ H₂SO₄, however, indicating their hydrolysis in the acid eluant. Solution ³¹P nuclear magnetic resonance spectroscopy was used to confirm the stability of the tested compounds when exposed to the membrane and the absence of significant concentrations of orthophosphate as trace contaminants in the compound preparations. Finally, for a series of tropical wetland soils from the Republic of Panama, we found negligible difference in eluted P concentrations determined by molybdate colorimetry and inductively coupled plasma optical emission spectrometry for both unfumigated and hexanol‐fumigated samples. We therefore conclude that although organic and condensed inorganic P compounds can be recovered by anion exchange membranes, this is likely to have limited impact on the analysis of soil samples.