Phosphorus Extraction Methods for Water Treatment Residual–Amended Soils

Abstract

Water treatment residuals (WTR) can adsorb tremendous amounts of phosphorus (P). A soil that had biosolids applied eight times over 16 years at a rate of 6.7 Mg ha^?1 y^?1 contained 28 mg kg^?1 ammonium–bicarbonate diethylenetriaminepentaacetic acid (AB‐DTPA), 57 mg kg^?1 Olsen, 95 mg kg^?1 Bray‐1, and 53 mg kg^?1 Mehlich‐III extractable P. To 10 g of soil, WTRs were added at rates of 0, 0.1, 1, 2, 4, 6, 8, and 10 g, then 20 mL of distilled deionized H₂0 (DI) were added and the mixtures were shaken for 1 week, filtered, and analyzed for soluble (ortho‐P) and total soluble P. The soil–WTR mixtures were dried and P extracted using DI, AB‐DTPA, Olsen, Bray‐1, and Mehlich‐III. Results indicated that all methods except AB‐DTPA showed reduced extractable‐P concentrations with increasing WTR. The AB‐DTPA extractable P increased with increasing WTR rate. The water‐extractable method predicted P reduction best, followed by Bray‐1 and Mehlich‐III, and finally Olsen.     

Phosphorus Nutrition of Lowland Rice in Tropical Lowland Soil

Rice is a main food crop for about half of the world's population, and phosphorus (P) is the main limiting nutrient in rice production in tropical lowlands. A greenhouse experiment was conducted to evaluate P requirements of lowland rice grown on a lowland soil (Inceptisol). Dry matter, grain yield, and yield-attributing characteristics were significantly (P < 0.01) influenced by P fertilization. Based on quadratic response, maximum shoot dry weight and grain yield were obtained with the application of 190 mg P kg^?1 of soil. Maximum panicle, tiller number, and plant height were obtained with the application of 177 192, and 175 mg P kg^?1 of soil, respectively. Mehlich 1–extractable P for maximum grain yield was 15.6 mg kg^?1 of soil. Variability in grain yield with plant growth and yield parameters was in the order of tiller > shoot dry weight > panicle number > spikelet sterility > plant height > grain harvest index > panicle length > weight of 1000 grains. Phosphorus uptake in shoot and concentration and uptake in grain significantly (P < 0.01) increased grain yield. However, variability in grain yield was greater with concentration and uptake of P in the grain. Similarly, P harvest index was also significantly associated with grain yield. Agronomic P-use efficiency, apparent P-recovery efficiency, and P-utilization efficiency decreased quadratically with increasing P rates, whereas physiological P-use efficiency increased quadratically and agrophysiological P-use efficiency decreased linearly with increasing P rates. Agrophysiological and utilization P-use efficiencies had significant positive correlation with grain yield.     

Potassium Requirements of Lowland Rice

Rice is a staple food for about 50 percent of the world’s population. Potassium (K) is absorbed in large amounts by rice plants and adequate amounts of this element are fundamental to improve productivity and maintain sustainability of the cropping systems. A greenhouse experiment was conducted to determine the adequate rate of K for lowland rice grown on a Brazilian Inceptisol. The K rates used were 0, 50, 100, 200, 400, and 600 mg K kg^?1 soil. Most of the growth, yield, and yield components were significantly and quadratically increased with increasing K levels. Based on a quadratic equation, maximum grain yield was obtained with the addition of 371 mg K kg^?1 soil. Maximum plant height and shoot dry weight were obtained at 414 and 398 mg K kg^?1 soil, respectively. Root growth (maximum length and dry weight) was also significantly increased in a quadratic fashion with the increasing K rate in the growth medium. Maximum root length was achieved at 58 mg K kg^?1 whereas maximum root dry weight was obtained with the addition of 394 mg K kg^?1 soil. Plant height, shoot dry weight, 1000-grain weight, root length, and root dry weight were significantly associated with grain yield. Hence, manipulation of these growth and yield components with the addition of K fertilizer can improve yield of lowland rice in varzea soils of central part of Brazil. Potassium uptake increased significantly in a quadratic fashion with increasing K rate. However, K-use efficiency (mg grain per mg K applied) decreased significantly with increasing K rate in a quadratic fashion. Maximum grain yield was obtained with 117 mg kg^?1 Mehlich 1–extractable K, base saturation of 53 percent, Mg saturation of 9 percent, K saturation of 2 percent, and Ca/Mg ratio of 4.     

Growth,yield and yield components of dry bean as influenced by phosphorus in a tropical acid soil

Phosphorus (P) deficiency is one of the most yield limiting factors for dry bean (Phaseolus vulgaris) production in tropical acid soils. Dry beans are invariably grown as mono-crops or as inter-crops under the perennial tropical crops. Information is limited regarding the influence of phosphorus fertilization on dry bean yield and yield components and P use efficiency in tropical acid soils. A greenhouse experiment was conducted to evaluate the influence of phosphorus fertilization on dry bean growth, yield and yield components and P uptake parameters. Phosphorus rates used were 0, 50, 100, 150, 200, and 250 mg P kg^?1 of soil. Soil used in the experiment was an acidic Inceptisol. Grain yield, shoot dry weight, number of pods, and 100 grain weight were significantly (P < 0.01) increased with phosphorus fertilization. Maximum grain yield, shoot dry matter, number of pods, and 100 grain weight were obtained with the application of 165, 216, 162, and 160 mg P kg^?1 of soil, respectively, as calculated by regression equations. Grain yield was significantly and positively associated with shoot dry weight, number of pods, P concentration in grain and total uptake of P in shoot and grain. Phosphorus use efficiency defined in several ways, decreased with increasing P rates from 50 to 250 mg P kg^?1 of soil. Maximum grain yield was obtained at 82 mg kg^?1 of Mehlich 1 extractable soil P. Results suggest that dry bean yield in Brazilian Inceptisols could be significantly increased with the use of adequate rates of phosphorus fertilization.     

Internal Boron Requirement of Young Sunflower Plants: Proposed Diagnostic Criteria

Abstract

In a greenhouse study, a significant increase in sunflower (Helianthus annuus L., cv. Hysun 33) dry matter yield was observed with boron (B) application to a B-deficient (hot water-extractable, 0.23 mg B kg^?1) calcareous soil of Missa series (Typic Ustochrept). Six rates of B, ranging from 0 to 8 mg B kg^?1 soil, were applied as H₃BO₃ along with adequate basal fertilization of nitrogen (N), phosphorus (P), potassium (K), and zinc (Zn). Four plants of sunflower were grown in each pot; two were harvested after 4 weeks of germination and the other two after 8 weeks. Maximum crop biomass was produced with 1.0 mg B kg ^?1, and application of ≥2.0 mg B kg^?1 proved toxic, resulting in drastic yield suppressions. Critical B concentration range for deficiency diagnosis in 4‐week‐old sunflower whole shoots appears to be 46–63 mg B kg^?1. However, critical concentration in 8‐week‐old plants was much less (i.e., 36 mg B kg^?l), presumably due to a dilution effect. As plant's internal B requirement can vary, in fact manifold, depending on the species, plant part, and plant age, only a relevant criterion can help in diagnosing the deficiency effectively.     

Integration of Soil pH with Soil‐Test Values of Zinc for Prediction of Yield Response in Rice Grown in Mollisols

Seventeen Mollisols having pH_(1:2) in the range of 6.00 to 8.42 were analyzed with five extractants, and the extractable zinc (Zn) ranges were 0.84 to 2.75 mg Zn kg^?1 soil for diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), 0.91 to 2.72 mg Zn kg^?1 soil for DTPA + ammonium bicarbonate (pH 7.6), 1.82 to 7.18 mg Zn kg^?1 soil for Mehlich 3, 1.22 to 3.83 mg Zn kg^?1 soil for ethylenediaminetetraacetic acid (EDTA) + ammonium carbonate, and 0.88 to 1.18 mg Zn kg^?1 soil for 1 mol L^?1 magnesium chloride (MgCl₂) (pH 6.0). Zinc extracted by DTPA (pH 7.3) and Mehlich 3 showed significant positive correlation with sand content, whereas only Mehlich 3 showed negative correlation with soil pH. All extractants showed significant positive correlation with each other except for 1 mol L^?1 MgCl₂‐extractable Zn, which had significant positive correlation with only Mehlich 3– and EDTA + ammonium carbonate–extractable Zn. A greenhouse experiment showed that Bray's percentage yield of rice was poorly correlated to extractable soil Zn but had a significant and negative linear correlation with soil pH (r = ?0.662, significant at p = 0.01). Total Zn uptake by rice had a significant positive correlation with 1 mol L^?1 MgCl₂– and Mehlich 3–extractable Zn. A proposed parameter (p extractable Zn + p OH^?) involving both soil extractable Zn and pH terms together showed significant and positive correlation with Bray's percentage yield and total Zn uptake of rice. The calculated values of critical limits of soil Zn in terms of the proposed parameter were 14.1699 for DTPA (pH 7.3), 13.9587 for DTPA + ammonium bicarbonate, 13.7016 for Mehlich 3, 13.9402 for EDTA + ammonium carbonate, and 14.1810 for 1 mol L^?1 MgCl₂ (pH 6.0). The critical limits of Zn in rice grain and straw were 17.32 and 22.95 mg Zn kg^?1 plant tissue, respectively.     

Comparison of Conventional and Polymer Coated Urea as Nitrogen Sources for Lowland Rice Production

Nitrogen (N) is one of the most yield limiting nutrients in lowland rice production. Improving N use efficiency is essential to reduce cost of crop production and environmental pollution. A greenhouse experiment was conducted with the objective to compare conventional and polymer coated urea for lowland rice production. Grain yield, straw yield, panicle density, maximum root length, and root dry weight were significantly increased in a quadratic fashion with the increase of N rate from 0 to 400 mg kg^?1 soil. Nitrogen source X N rate interactions for most of these traits were not significant, indicating that lowland rice responded similarly to change in N rates of two N sources. Based on regression equations, maximum grain yield was obtained with the application of 258 mg N kg^?1 soil and maximum straw yield was obtained with the addition of 309 mg N kg^?1 soil. Nitrogen use efficiency (grain yield per unit of N applied) was maximum for polymer coated urea compared to conventional urea. Root length and root dry weight improved at an adequate N rate, indicating importance of N fertilization in the absorption of water and nutrients and consequently yield. Polymer coated urea had higher soil exchangeable calcium (Ca) and magnesium (Mg), Ca saturation, Mg saturation, base saturation, and effective cation exchange capacity compared to conventional urea. There was a highly significant decrease in soil exchangeable potassium (K) with increasing N rates at harvest of rice plants.     

Phosphorus Nutrition of Upland Rice,Dry Bean,Soybean, and Corn Grown on an Oxisol

Rice, dry bean, corn, and soybean are important food crops. Phosphorus (P) deficiency is one of the most yield-limiting factors for these crops grown on highly weathered Brazilian Oxisols. Four greenhouse experiments were conducted to determine P requirements of these four crops. The P levels used were 0, 50, 100, 200, and 400 mg kg^?1. Growth, yield, and yield components evaluated of four crop species were significantly increased with the application of P fertilization. Most of the responses were quadratic in fashion when the P was applied in the range of 0 to 400 mg kg^?1. Maximum grain yield of upland rice was obtained with the application of 238 mg P kg^?1 of soil, maximum dry bean grain yield was obtained with the application of 227 mg P kg^?1 of soil, and maximum grain yield of soybean was obtained with the application of 224 mg P kg^?1 of soil. Maximum shoot growth of corn was obtained with the addition of 323 mg P kg^?1 of soil. Most of the growth and yield components had significant positive association with grain yield or shoot dry weight. Phosphorus concentration and uptake were greater in the grain compared to straw in upland rice and dry bean plants. Overall, P-use efficiencies decreased with increasing P rates.     

Divergent Relationships of Phosphorus Soil Tests in Temperate Grassland Soils

Abstract

Various soil tests are used to estimate phosphorus (P) availability for both crop uptake and potential loss to water. Conversion equations may provide a basis for comparison between different tests and regions, although the extent to which information can be interchanged is uncertain. The objective was to determine and quantify relationships between specific soil test extractants for samples taken annually in October and February over 4 years from four sites in each of eight soil series under grassland. The extractants comprised Mehlich‐3, Morgan, Olsen, Bray‐1, lactate–acetate, CaCl₂ (1∶2 and 1∶10 soil–solution ratios), and resin. The results showed distinct relationships for each soil series, for which individual lines regression models (different intercepts and slopes) were superior to a single conversion equation across all soils. The ensuing difference between soils was large and ranged from 1.9 to 8.0 and 9.2 to 15.6 mg kg^?1 P for Morgan and Olsen, respectively, at 20 mg kg^?1 Mehlich‐3 P. Generally, the environmentally oriented tests CaCl₂ and resin correlated best with Morgan. Some soil‐specific limitations were also observed. CaCl₂ was less efficient than Morgan, and Morgan less efficient than Mehlich‐3 on a high Fe–P soil derived from Ordovician‐shale diamicton, compared with the general trend for other soils. This finding suggests that further disparity may arise where evaluation of critical, or other, limits across regions involves even a limited sequence of tests.     

Boron Fertilization and Evaluation of Four Soil Extractants: Russet Burbank Potato

Yield‐response correlations with old and improved soil extraction methods for boron (B) are needed. Russet Burbank potato (Solanum tuberosum L.) was grown with two, four, and six B treatments applied in 2004, 2005, and 2006, respectively. Zero and 1.1, 2.2, or 3.4 kg B ha^?1 soil and 0.22 or 0.28 kg B ha^?1 foliar treatments were applied. Boron fertilization did not significantly increase tuber yield or quality despite initially low hot‐water‐extractable B (0.34–0.50 mg kg^?1), although postseason B for unfertilized treatments increased (0.51–0.57 mg kg^?1). Soil‐applied B generally reflected B application relative to the untreated control and the low foliar rates in all three years for the four soil extractions utilized [hot water, pressurized hot water, diethylenetriaminepentaacetic acid (DTPA)–sorbitol, and Mehlich III]. Boron content of potato petiole did reflect application of B in 2 years, but tuber and peel tissues did not consistently reflect application of B.     

Appraisal of Some Soil Tests for Zinc Availability to Late‐Sown Wheat Grown in Mollisols

Abstract

Five soil extractants, namely, 0.005 M diethylene triamine pentaacetic acid (DTPA) (pH 7.3), 0.005 M DTPA+1 M ammonium bicarbonate (pH 7.6), Mehlich 3, 0.01 M ethylene diamine tetraacetic acid (EDTA)+0.05 M ammonium carbonate (pH 8.6), and 1 M magnesium chloride (MgCl₂) (pH 6.0), were evaluated to predict the response of wheat to zinc (Zn) application in Mollisols. These extractants could be arranged in the following decreasing order of their Zn extracting power: Mehlich 3>0.005 M DTPA+1 M ammonium bicarbonate>0.01 M EDTA+0.05 M ammonium carbonate>0.005 M DTPA>1 M MgCl₂. The critical limits of Zn in soil, below which the yield response to late sown wheat (var. UP‐2338) to Zn application could be expected, were 0.57 mg 0.005 M DTPA (pH 7.3) extractable and 1.72 mg Mehlich 3–extractable Zn kg^?1 soil. The critical limit of Zn in whole shoot at 60 days after emergence was found to be 26.1 mg Zn kg^?1 plant tissue. The DTPA and Mehlich 3–extractable soil Zn also correlated significantly and positively with Zn concentration in whole shoot at 60 days after emergence and total Zn uptake by wheat at harvest.     

Yield and Yield Components and Phosphorus Use Efficiency of Lowland Rice Genotypes

Phosphorus deficiency is main constraints for lowland rice production in various rice producing regions of the world. A greenhouse experiment was conducted using lowland (Inceptisol) soil with the objective to determine response of seven lowland rice (Oryza sativa L.) genotypes to phosphorus fertilization and to evaluate their phosphorus (P) use efficiency. Phosphorus treatments included control (0 mg P kg^?1) and 200 mg P kg^?1 of soil. Plant height and shoot dry weight were significantly (P < 0.001) influenced by P treatments. Phosphorus X genotypes interaction was significant for shoot dry weight, indicating different response of genotypes under two P levels. At low P level, none of the genotypes produced grain yield, indicating original P level in the soil was too low for lowland rice yield. However, genotypes differed significantly in grain yield at high P level. Panicle number, panicle length, and thousand grains weight had a significant quadratic association with grain yield. However, spikelet sterility had a significant linear negative association with grain yield. The P use efficiency expressed as agronomic efficiency (AE), physiological efficiency (PE), agro-physiological efficiency (AP), apparent recovery efficiency (ARE), and utilization (UE) were significantly different among genotypes. These efficiencies were having significantly positive association with grain yield, with exception to ARE, indicating improving grain yield with improved P use efficiencies in rice.     

Nitrogen,Phosphorus, and Potassium Fertilization of a Coastal Plain Cotton–Peanut Rotation

Abstract

A cotton (Gossypium hirsutum)–peanut (Arachis hypogaea L.) rotation is widely practiced in the southern coastal plain following the reemergence of cotton as a major crop in the 1990s. Very few plant nutrition studies have been conducted in the coastal plain (CP) with modern cotton varieties and none with the cotton–peanut rotation. Experiments with varying rates of nitrogen (N), phosphorus (P), and potassium (K) were conducted to determine if the recommendations from soil tests provide adequate nutrition for maximizing profit when yield goals are Georgia state averages, due to other conditions. From 1996 through 1998, N, P, and K experiments were conducted in cotton crops, and P and K experiments were conducted in peanut crops on Tifton loamy sand. Initial Mehlich‐1 P was 2 to 3 mg/kg (“low”) and Mehlich‐1 K was 50 to 64 mg/kg (“medium” for cotton and “high” for peanut). Each crop was grown each year. State average yields of cotton and peanuts were produced. There was no response in cotton yield to N rates from 34 to 136 kg N/ha. Lack of response may have been due to the fact that the field had not been in production for several years prior to 1996 and there was ample soil mineral N. In 1997 and 1998, residual N provided by N fixation by the previous peanut crop appeared to be sufficient. Maximum profit from P fertilization in cotton was attained at 50 kg P/ha, the recommendation from the soil test. However, a University of Georgia Cooperative Extension Service recommendation to double the P rate for new land with a “low” Mehlich‐1 P soil test was not validated. Cotton yield did not respond to K fertilization even though an application of 55 kg K/ha/year was recommended from the soil test. Peanut yield and grade did not respond to either P or K fertilization. The recommendation from the soil test was 40 kg P/ha/year and no K. Estimates of P removal were 11 kg/ha for cotton and 8 mg/ha for peanut crops. Estimates of K removal were 25 kg/ha for cotton and 22 kg/ha for peanut crops. Over 3 years, soil P was not depleted, but soil K was depleted. Approximately 12 kg P/ha were required to raise soil test P 1 mg/kg and 18 kg K/ha were required to raise soil test K 1 mg/kg (49 lb. P₂O₅ to increase the P test 1 lb./acre, 38 lb. K₂O to raise the K test 1 lb./acre). Additional studies are needed, but the current studies suggest that revisions in recommendations are needed for both cotton and peanut crops.     

Zinc,Copper, Boron and Iron Requirement of Upland Rice Grown on a Brazilian Oxisol

Deficiency of micronutrients increasing in field crops, including upland rice in recent years. The objective of this study was to determine requirement of zinc (Zn), copper (Cu) boron (B) and iron (Fe) for upland rice grown on a Brazilian Oxisol. The levels used were: Zn (0, 10, 20, 40, and 80 mg kg^?1), Cu (0, 5, 10, 20 and 40 mg kg^?1), B (0, 5, 10, 20 and 40 mg kg^?1) and Fe (0, 250, 500, 1000, and 2000 mg kg^?1). Plant height, straw yield, grain yield, panicle number and grain harvest index (GHI) were significantly improved with the addition of these micronutrients. Root growth was also improved with the application of micronutrients, except with the addition of B. Maximum grain yield was obtained with the addition of 51 mg Zn, 24 mg Cu, 5 mg B kg^?1, and 283 mg Fe kg^?1 soil. Similarly, maximum straw yield was obtained with the addition of 38 mg Zn, 17 mg Cu, 6 mg B kg^?1, and 1500 mg Fe kg^?1 soil. Maximum plant height was obtained with the addition of 54 mg Zn, 10 mg B kg^?1, and 1197 mg Fe kg^?1 soil. Copper did not affect plant height significantly. Maximum panicle number was obtained with the addition of 22 mg Cu kg^?1, 3 mg B kg^?1, and 1100 mg Fe kg^?1 soil. Zinc did not affect panicle number significantly. Maximum GHI was obtained with the addition of 61 mg Zn kg^?1, and 8 mg B kg^?1. Zinc was had a linear increase in GHI in the range of 0 to 80 mg kg^?1, and Fe showed a negative relationship with GHI.     

Effects of Broiler Litter Management Practices on Phosphorus,Copper, Zinc,Manganese, and Arsenic Concentrations in Maryland Coastal Plain Soils

Abstract

The objective of this research was to assess the long‐term effects of broiler litter applications on soil phosphorus (P), copper (Cu), zinc (Zn), manganese (Mn), and arsenic (As) concentrations in Chesapeake Bay watershed Coastal Plain soils. Litter and soil samples were collected from 10 farms with more than 40 years of broiler production and from wooded sites adjacent to fields and were analyzed for P and metal contents. Averaged over farms, total P and metal concentrations in the litter were 12.8 g kg^?1 P and 332, 350, 334, and 2.93 mg kg^?1 Cu, Zn, Mn, and As, respectively. Surface (0–15 cm) soil pH values were greater than (5.7–6.4) the 0‐ to 15‐cm depth at wooded sites (3.5–4.3). Surface soil Bray 1 P values (149–796 mg kg^?1) in amended fields were greater than wooded sites (4.4–17 mg kg^?1). The 1N nitric acid (HNO₃)–extractable metal concentrations were higher in amended soils than in wooded areas and were 7.7–32, 5.7–26, 12.3–71, and 0.6–3.0 mg kg^?1 for Cu, Zn, Mn, and As, respectively, compared to 0.76–14, 4.6–22, 1.6–70, and 0.14–0.59 mg kg^?1 for the same metals, respectively, in wooded areas. Results from this study demonstrated that long‐term broiler litter applications have altered the chemical properties of the Coastal Plain soils of the Maryland Eastern Shore. Metal concentrations were low in the surface layer of amended fields and typically decreased with depth. Phosphorus additions rather than metals are most likely to contribute to the degradation of the Chesapeake Bay watershed.     

Comparison of Soil P Test Procedures for St. Augustinegrass

St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze] is a home lawn grass widely used in the southern United States. At present, phosphorus (P) fertilization of St. Augustinegrass is based primarily on Mehlich 1 P test. One criticism of Mehlich 1 extractant is that it extracts some fraction of soil P pool that is not available to plants, whereas, iron (Fe) oxide P and water‐extractable P methods are reported to be better related to plant growth in some cases. Literature relative to the soil test procedure comparison for St. Augustinegrass was not found. The objective of this study was to evaluate Mehlich 1 P, Fe oxide P, and water‐extractable P to identify the most suitable soil test method for St. Augustinegrass growth. Established pots of ‘Floratam’ were subjected to P application of 0, 0.14, 0.27, 0.54, and 1.07 g m^?2 every 4 wk for 12 wk. Measurements included tissue growth rates, tissue P concentration, soil Mehlich 1 P, Fe oxide P, and water‐extractable P concentrations. Phosphorus application increased soil test P concentrations. Soil Mehlich 1 P, Fe oxide P, and water‐extractable P concentrations were closely correlated to each other. Three soil test P levels and tissue P concentrations were highly correlated with Mehlich 1 P, which best predicted tissue P levels. Three soil test P levels were also closely correlated to the St. Augustinegrass top growth rate. Critical minimum Fe oxide P and water‐extractable P concentration was 3 mg kg^?1. Overall, Mehlich 1 P was the best soil P test for St. Augustinegrass among the three extractants tested.     

Critical soil phosphorus of a low‐P loess‐derived soil as affected by storage temperature

Abstract

Overwintering soil temperature may influence crop response to phosphorus (P) and indices of P availability in the humid, temperate, transitional climate of Tennessee. The effects of P fertilization and soil incubation temperature on sorghumsudangrass (Sorghum bicolor x S. Sudanese) grown on a Typic Hapludalf was investigated in a greenhouse study. In order to determine the effect of temperature on P availability, soils were incubated prior to cropping, at a constant temperature of 6°C or an average diurnal temperature of 24 and 36°C. Reagent grade Ca(H₂PO₄)₂.H₂O was used as the fertilizer source and applied at rates of 0, 10, 20, and 30 mg P kg^‐1 for the first test and 0, 20, 40, 60, and 80 mg P kg_‐ ¹ for the second test. Critical P concentration in the shoots for optimum yield was found to be 1.3 mg g‐¹, corresponding to soil solution and labile P concentrations of 5.5 μmol L^‐1 and 167 μg g^‐1, respectively. Optimum yield occurred for applications of >65 mg P kg^‐1 and was unaffected by soil incubation temperature. Applied P rates affected extractable P by five chemical extractants (Bray I, Bray II, Mehlich I, Mehlich III, and Mississippi), but soil incubation temperature had no affect. The extractants, however, were poorly correlated to plant P uptake and no one extractant appeared preferable to the others as an indicator of P availability.     

Agronomic Evaluation of Dry Bean Genotypes for Potassium Use Efficiency

Dry bean is an important legume worldwide, and potassium (K) deficiency is one of the important constraints for bean production in most of the bean growing regions. A greenhouse experiment was conducted with the objective to evaluate fifteen dry bean genotypes grown on a Brazilian lowland (Inceptisol) United States Soil Taxonomy classification and Gley humic Brazilian Soil Classification system), locally known as “Varzea” soil. The K rate used was 0 mg kg^?1 (low, natural soil level) and 200 mg kg^?1 (high, applied as fertilizer). Straw yield, seed yield, pods per plant, seeds per pod, 100 seed weight, and seed harvest index were significantly increased with the addition of K fertilizer. These traits were also significantly influenced by genotypic treatment. Similarly, root length and root dry weight were also influenced significantly by K and genotype treatments. The K X genotype interactions for most of these traits were also significant, indicating variation in these traits with the variation in K level. Based on seed yield efficiency index (SYEI), genotypes were classified as efficient, moderately efficient, and inefficient in K use efficiency. Maximum grain yield was obtained with 74 mg K kg^?1 extracted by Mehlich 1 extracting solution. Similarly, K saturation required for maximum grain yield was 1.1%.     

Zinc and copper toxicity in peanut,soybean, rice,and corn in soil mixtures

Abstract

Applications of zinc (Zn) and copper (Cu) at excessive rates may result in phytotoxicity. Experiments were conducted with mixtures of soils that were similar except for their Zn and Cu levels. The critical toxicity levels (CTL) in the soils and plants for these elements were determined. Peanut (Arachis hypogaea L.), soybean [Glycine max (L.) Merr.], corn (Zea mays L.), and rice (Oryza sativa L.) were the crops grown. One soil mixture had Mehlich 3‐extractable Zn concentrations up to 300 mg dm^‐3 with no corresponding increase in soil Cu; two soil mixtures had soil Zn concentrations up to 400 and 800 mg dm^‐3 with a corresponding increase in soil Cu up to 20 and 25 mg dm^‐3, respectively; and four soil mixtures had no increase in soil Zn, but had Mehlich 1‐extractable Cu concentrations from 6 to 286 mg kg^‐1. Under a given set of greenhouse conditions, the estimated Mehlich 3‐extractable Zn CTL was 36 mg dm^‐3 for peanut, 70 mg dm^‐3 for soybean, between 160 and 320 mg dm^‐3 for rice, and >300 mg dm^‐3 for corn. No soil Cu CTL was apparent for peanut or soybean, but for corn it was 17 mg dm^‐3 and for rice 13 mg dm^‐3. With different greenhouse procedures and the Mehlich 1 extractant, the soil CTL for rice was only 4.4 mg kg^‐1. Therefore, peanut and soybean were more sensitive to Zn toxicity, whereas corn and rice were more sensitive to Cu toxicity. Plant Zn CTL for peanut was 230 mg kg^‐1, while that for soybean was 140 mg kg^‐1. Copper appeared to be toxic to corn and rice at plant concentrations exceeding 20 mg kg^‐1.     

Soil‐Test Methods for Florida Sands Treated with an Aluminum–Water Treatment Residual and Various Phosphorus Sources

Use of aluminum (Al)–rich water treatment residuals (Al‐WTR) has been suggested as a practice to immobilize excessive phosphorus (P) in Florida soils that could represent an environmental hazard. Fertilizer P requirements can differ in WTR‐amended and unamended soil, so careful selection of soil‐testing methodology is necessary. Acidic extractants can dissolve WTR sorbed P and overestimate plant‐available P. We evaluated the suitability of the Mehlich 1 P (M‐1P) and other agronomic soil‐test procedures in an Al‐WTR‐treated Florida soil. Bahiagrass (paspalum notatum Fluggae), ryegrass (Lolium perenne L.), and a second bahiagrass crop were grown in succession in a Florida topsoil amended with four sources of P at 44 kg P ha^?1 (P‐based rates) and 179 kg PAN ha^?1 [nitrogen (N)–based rates] and three WTR rates (0, 10, and 25 g kg^?1 oven‐dry basis). Both water‐extractable P (WEP) and iron (Fe) strip P (ISP), but not M‐1P, values of soil sampled at planting of each grass were greater in the absence than in the presence of WTR. Total plant P uptake correlated with WEP (r² = 0.82^***) and ISP (r² = 0.75^***), but not M‐1P (r² = 0.34^***). Correlations of the dry‐matter yield, P concentration, and P uptake of the first bahiagrass were also better with WEP and ISP than with M‐1P values. However, regression of plant responses with M‐1P improved after the first crop of bahiagrass. Both WEP and ISP values were better predictors of available soil P than M‐1P in a field study with same four P sources surface applied to established bahiagrass at the same two P rates, with and without WTR. Both WEP and ISP are recommended as predictors of P adequacy in soils treated with WTR, especially for soils recently (< 5 months) treated with Al‐WTR.