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Numerous potential benefits have been cited for the inclusion of tropical legumes in pastures, but few commercial successes have been realized. Information is needed on even the most basic aspects of tropical legume culture. The study herein was designed to determine rates of lime and P for maximum yield of three tropical legumes, and to estimate the rates resulting in maximum economic return under field conditions. An acid infertile Spodosol was amended with lime up to 4000 kg ha−1and P up to 80 kg ha−1. Equations relating herbage yield during the first 2 years of growth to rates of lime and P were developed. All three legumes (Aeschynomene americanaL., Macroptilium atropurpureumUrb., and Desmodium heterocarponDC.) responded positively to both lime and P. Maximum yield of Desmodiumwas obtained at lime and P rates of 2740 and 75 kg ha−1, respectively. Maximum calculated herbage yields of Aeschynomeneand Macroptiliumwere obtained at lime and P rates somewhat in excess of maximum treatment levels. An economic analysis that considered hay as the produced product revealed that maximum economic returns occurred at lime and P rates only slightly lower than those for maximum yield. Considering protein as the product, for all three legumes lime and P rates of approximately 3000 and 75 kg ha−1produced maximum yield and maximum economic return.

The generalization is often made that tropical legumes show little or no response to lime, even in acid soils low in Ca. Phosphorus responses, however, are generally observed. The effect of lime in an acid, virgin spodosol (Oldsmar fs) in southern Florida plots was investigated. Significant yield responses to lime and P were observed. Maximum total annual dry matter production of centro (Centrosema pubescensBenth.), desmodium (Desmodium heterocarponDC.), stylo (Stylosanthes guyanensisSwartz), and ‘Siratro’ (Macroptilium atropurpureumUrb.) required lime applications of about 2,200 kg/ha. Regression analyses suggested that centro and Siratro might respond to higher lime rates if combined with P rates higher than those used in the study. Calculated optimum P rates ranged from 45 to 78 kg/ha, with desmodium requiring the least. Liming beyond the optimum rate appeared to seriously reduce production of desmodium and stylo.

Nitrogen and potassium leaching from a fertilizer band in sand soils was reduced by creating a mulch of water repellent soil over the band using a siliconate spray. Best results were obtained using a 1% siliconate spray in quantities sufficient to penetrate about 3 cm over a region 20 cm wide, on the flat surface of raised vegetable beds. Mulches created on peaked beds were ineffective in reducing leaching, probably due to erosion of the mulch. Sweet corn (Zea maysvar. rugosa) yields were comparable to those obtained by protecting N and K with plastic mulch or by applying N and K in split applications.

Taro (Colocasia esculenta) is a wetland plant that can be used as a fuel stock for biomass conversion into various energy forms. Predicting the biomass production is important in developing the optimal harvesting schedule, but information needed to predict production is unavailable. The objective of this study was to predict the tare biomass production based on leaf area index information. Cultivar Lehua Maoli was planted with a space of 0.5 m between plants in 1981. In 1982, the same cultivar was planted with spaces of 0.2, 0.4, and 0.6 m between plants. Dry biomass and leaf area (LA) were monitored monthly in 1981 and bimonthly in 1982. Leaf area was best estimated from leaf dry biomass (LDB) by the equation LA = 223 LDB (r2=0.91). Dry biomass was linearly related to cumulative monthly mean leaf area index until cumulative monthly mean leaf area index reached 10 (r2=0.80 to 0.97). These relationships could be useful for predicting taro biomass production, both as a research tool and as a guide for scheduling commercial harvest.

Rice (Oryza sativaL.) and sugarcane (Saccharumspp.), grown on organic soils of the Everglades, have been shown to respond favorably to the application of Si from calcium silicate slag. Since these crops may be grown in rotation, it is important to know if slag applied to one crop will benefit the second crop. The objective of the study was to determine the response of rice and sugarcane grown on a Terra Ceia muck (Euic, hyperthermic Typic Medisaprist) to calcium silicate slag applied prior to planting rice, and to slag applied before the planting of sugarcane. Five rates of slag were applied for production of a rice crop, after which time the same plots were planted to sugarcane. Other plots received the same rates of slag just prior to planting sugarcane. Slag applications increased both rice straw Si and sugarcane leaf Si concentrations. A single application of slag prior to planting rice increased production of both the rice and sugarcane crops in the rotation. The combined plant and ratoon rice grain yields were significantly increased 50% by slag application. Slag application also increased harvested cane (biomass) yields 23%, and sugar yields by 25%. Somewhat greater sugarcane plant responses were observed from slag applied immediately before planting than from slag applied before the rice and cane rotation treatment. On the average, slag applied at 20 Mg ha−1before rice increased sugar yield by 16%, compared to a 21% increase when slag was applied before cane.

Although plant population effects on crop performance have been thoroughly investigated in transplanted rice (Oryza sativaL.), less information is available for drill‐seeded rice. Previous studies evaluating the response of rice cultivars to various seeding rates and row spacings were performed before semi‐dwarf cultivars were available in areas where drill‐seeding is practiced. Two contrasting plant types, tall (cv. Lebonnet) and semi‐dwarf (cv. Bellemont and Lemont), were drill‐seeded at rates of 50, 100, and 150 kg seed ha−1in 0.15‐, 0.20‐, and 0.25‐m row spacings in three tests conducted on an organic soil. Narrow row spacings increased grain yield for both plant types when reproductive growth occurred during a period of relatively high solar radiation and moderate temperatures. Increased seeding rates increased panicles per square meter in all tests for both plant types. This increase was compensated for by decreased filled grain number per panicle, resulting in no significant yield differences among seeding rates. It appears that seeding rates of 80 to 100 kg ha−1are sufficient to obtain optimum stands in southern Florida.

Manganese deficiency of ‘Tifgreen’ bermudagrass (Cynodon ✕ magenissiiHurcombe) turf has been observed in South Florida when soil pH exceeded 7 as a result of irrigation with alkaline water. A 2‐year field study on Pompano fine sand (a siliceous, hyperthermic, typic Psammaquent) was designed to evaluate three approaches to correcting this deficiency: 1) soil pH reduction with acid forming N sources, 2) Mn fertilization at rates up to 5 g/m2using MnSO4, a Mn‐chelate, or a Mn‐frit, and 3) MnSO4fertilization in combination with a series of fungicidal drenches for suppressing Mn‐oxidizing soil fungi. Sulfate and chelate Mn sources provided short‐term correction of the deficiency, but little response to the frit source was noted. Sustained correction was achieved with MnSO4in combination with the fungicidal drenches. However, adequate Mn nutrition was obtained even in the absence of Mn fertilization when soil pH was maintained below 7 with acid‐forming N sources. This treatment appears most suitable for turfgrass, since considerable N commonly is used in turfgrass production.

The study was conducted to determine the feasibility of using a tensiometer‐controlled irrigation system to reduce N leaching in turfgrass while maintaining acceptable growth. Bermudagrass (Cynodon dactylon× C. transvaalensis) was grown on a sand soil (Pomano fine sand, a siliceous, hyperthermic Typic Psammaquent) during a series of 2‐month (bimonthly) cycles. Irrigation was applied either daily (Daily irrigation), or when permitted by tensiometer soil moisture sensors (Sensor irrigation). Nitrogen at the rate of 5 g m−2month−1was applied bimonthly as NH4NO3, (AN) or sulfur‐coated urea (SCU), or as NH4NO3, through the irrigation system with each irrigation (Fertigation). The effect of these treatments on turfgrass color, clipping weights, and on tissue N content were measured. Nitrogen was determined in soil water samples obtained on a near daily basis from below the rootzone using ceramic cup suction lysimeters. Nitrogen leaching ranged from 56% to less than 1% of that applied, depending on treatment and cycle. The AN source combined with Daily irrigation produced the greatest N losses (22 to 56%), and Fertigation with Sensor irrigation produced the smallest losses (

Rice (Oryza sativaL.) drill‐seeded in certain Histosols in the Everglades Agricultural Area germinates well, but after a few weeks it becomes chlorotic and grows poorly. The condition is termed “rice‐seedling chlorosis.” After flooding, chlorotic seedlings generally assume normal color, except that some seedling mortality occurs, particularly in areas with excessively deep water. Studies were conducted to identify soil and cultivar susceptibility to seedling chlorosis, and then to develop methods for preventing its occurrence. Problem soils were identified on the basis of their total Fe content. Seedling chlorosis occurred in soils containing up to 3.4 g Fe kg−1. Susceptible soils produced a nearly white ash when heated in a muffle furnace for 2 h at 550 °C. Seedling chlorosis was alleviated in all cultivars examined by drilling water‐soluble Fe compounds with the seed at rates of 20 to 30 kg Fe ha−1. The effect of seedling chlorosis on yield varied with cultivar and, to some extent, with experimental conditions. The cv. Leah was very susceptible to chlorosis, and yield was increased by Fe treatment. By contrast, even though visual symptoms were apparent, yield of cv. Labelle evidently was not reduced by seedling chlorosis because Fe treatment did not increase yield. Yield of cv. Lebonnet increased with Fe treatment in two out of three trials. Although the studies did not permit determination of the cause of seedling chlorosis, it appeared that the chlorosis did not result from a simple Fe deficiency.

Rice (Oryza sativaL.), one of the world's most widely grown grain crops, is seldom grown on Histosols, in part because of many problems related to plant nutrition. Studies were conducted on Terra Ceia muck (Typic Medisaprists) in the Everglades to determine the effect of calcium silicate slag on ‘Lebonnet’ rice production. Grain yields were increased in excess of 30% in each of 3 yr by preplant application of slag at 10 Mg ha−1or more. Rice in plots receiving slag had greater height, greater number of panicles per square meter, heavier grains, and less disease. Although the slag contained a number of plant nutrients, Si appeared to be the factor most responsible for the observed results. A positive linear relationship was observed in all years between straw Si and grain yield. First crop straw averaged 1.3, 5.0, and 5.9 dag Si kg−1in plots receiving 0, 10, and 20 Mg slag ha−1, respectively. A first crop straw Si concentration <3.0 dag Si kg−1was associated with reduced rice yield. Perhaps Si application should be considered in other regions when difficulties are encountered with rice production on Histosols.

Crop growth and yield on sand soils is often limited by low N availability due to leaching losses from the soil. This study was initiated to determine if sulfur‐coated urea (SCU) could supply adequate N nutrition and eliminate the need for repeated N applications for sugarcane (Saccharumspp.) grown on previously uncropped Immokalee fine sand in southern Florida. Single applications of two SCU's were compared with split applications of (NH4)2SO4(AS), each at three N rates, 56, 112, and 168 kg/ha. Application of SCU at planting in November resulted in excellent growth and high leaf N concentrations in the spring but did not provide optimum N throughout the growing season. Leaf N concentrations in late summer and tonnages of sugarcane and sugar for SCU plots approached, but did not equal, those attained with four applications of AS. Higher tonnages were recorded for the slower releasing SCU than for the faster releasing source but both SCU sources released large amounts of N before the warm summer months when N is required in the highest quantities. The data indicate that SCU's which release N more slowly and/or a later application date should provide better N nutrition and eliminate the need for several split applications of soluble sources.

Nitrogen release from sulfur‐coated urea and K release from S‐coated KCl were examined by several techniques under field conditions in three south Florida sand soils in order to assist in the interpretation of plant response data and to provide insight into the use of three slow‐release fertilizer materials. Decreased thickness of S coating, higher temperatures and higher moisture generally favored nutrient release. However, considering the range of field conditions involved in the studies, variations in N and K release were comparatively small. Release was rapid during the first 6 months, averaging 70–80% of that applied, but was much slower thereafter.

Acid dissociation equilibrium constants and rate constants for disulfide interchange reactions have been measured in 50% methanol at low ionic strength for peptides containing cysteines with local ionic neighboring groups. These physical constants may be correlated by separation of free energy contributions into solvent-independent and solvent-dependent factors. The former represent inductive effects which may be evaluated by extrapolation of pKa values to the limit of infinite ionic strength. These solvent-independent contributions give Br onsted coefficients consistent with previously reported values for disulfides with neutral constituents. The solvent-dependent contributions represent thru-solvent electrostatic effects and are consistent with the form of the Bjerrum relationship correlating molecular charges, intergroup distances, and the dielectric constant of the solvent. These results provide a quantitative framework for developing strategies for employing coulombic interactions to direct disulfide pairing in synthetic polypeptides.

Microscopic disulfide-exchange rate constants have been measured for the formation and opening of small disulfide loops in reactions between glutathione and peptides containing 2 cysteines. Twelve cysteine-Xm-cysteine peptides have been studied, where Xis an amino acid and mis the number of amino acids between the cysteines. Homopolymers of alanine for m equaling 0-5 are evaluated, as well as X1and X2series employing glycine, valine, or proline. Equilibrium constants Kcfor loop closing are only slightly dependent on the nature of X. Loops with even values of mgenerally are favored relative to loops with odd values. Kcincreases in the rank order X1, X3, X0, X5, X4, and X2. Formation of a disulfide between sequentially adjacent cysteines therefore is not especially difficult. The dependence of Kcon the odd-even nature of m is compared with similar patterns observed both in statistics of disulfide formation in naturally occurring proteins and in theoretical studies of peptide cyclization. The relative equilibrium populations of intramolecular disulfides in peptides containing cysteine-cysteine-cysteine and cysteine-serine-cysteine-serine-cysteine clusters are consistent with predictions based on the values of Kcin the two-cysteine peptides.