A pulse‐flooding hydroponic system for nutrient culture

Abstract

A hydroponic system for nutrient plant culture, designed to overcome the problems of algal contamination, adequate aeration and physical support for the plants is presented. It is based on intermittent floodings of the growth pots, containing lapilli tuff as a supportive medium, with a nutrient solution. The substrate used is capable of holding sufficient water for a relatively long period, yet it maintains good aeration of the roots. The system is simple, inexpensive and requires a low power supply. Detailed technical data are given.     

Salinity effects on annual bedding plants in a peat‐perlite medium and solution culture

Annual vinca (Catharanthus roseus (L.) G. Don ‘Pink Carpet'), geranium (Pelargonium x hortorum L. H. Bailey ‘Jackpot'), and marigold (Tagetes erecta L. ‘First Lady') were grown in a sphagnum peat moss and perlite medium. Plants were irrigated with solutions of different salinity by the addition of 0.0, 1.0, 2.0, 4.0, and 8.0 g/1 of a NaCl and CaCl₂ mixture resulting in solution electrical conductivity (EC) values of about 1.3, 3.0, 4.5, 7.9, and 13.9 ds/m, respectively. In another experiment marigold and geranium were grown in solution culture containing the same salt mixture at 0.0, 1.0, 4.0, and 8.0 g/1 with EC values of 1.4, 3.0, 7.4, and 12.5 ds/m, respectively. All species showed some salinity tolerance up to 2.0 g/1 in peat‐perlite and 1.0 g/1 in solution culture as growth reductions were below 10% and no foliar injury occurred. Foliar injury occurred on marigold and geranium, but not annual vinca, at 4.0 and 8.0 g/1 in both growing media. On a concentration basis, recently mature leaves sampled from marigold grown in peat‐perlite contained more chloride (Cl) but less sodium (Na) than geranium and annual vinca. However results of the solution culture experiment showed that, with the exception of 1.0 g/1 treatment, geranium and marigold plants absorbed the same amount of Cl and Na when content was expressed on a mg/g dry weight basis. The low Na concentration in marigold leaves was a reflection of restricted translocation of Na from the roots to the shoots.     

Iron‐Enriched Azolla as a slow‐release biofertilizer for cucumber plants grown in a hydroponic system

The unique ability of dried plant residues Azolla to adsorb iron (Fe) was employed to formulate and test an organic Fe biofertilizer. A simplified experimental system was established to examine the effectiveness of Fe‐enriched Azolla as a source of Fe for the remedy of Fe‐deficient plants. The optimal Fe‐enrichment level needed to achieve a complete recovery of starved plant by the Fe‐Azolla complex was tested using a bioassay system of hydroponically grown cucumbers. Dried Azolla plants were mixed a with a solution of ferrous sulfate (FeSO₄) at pH 2.0, rinsed, and dried to form organic, compact material containing 4% (w/w) Fe bound to Azolla. The Fe‐Azolla complex was applied to the nutrient solutions of Fe‐deficient cucumber seedlings. Growth rates and development measurements as well as chlorophyll and the Fe‐containing catalase activity tests have been performed. The effect of the slowly released Fe in correcting Fe deficiency were followed for three weeks and compared with the efficiency of additions of several synthetic Fe chelates. Iron‐starved plants exhibited fast regreening of the chlorotic interveinal tissues after the addition of Fe‐Azolla complex to the nutrient solutions. Iron starvation decreased the activity of catalase. Iron‐treated‐starved plants exhibited recovery of catalase activity compared to the low level activity measured untreated Fe‐starved plants. Iron‐enriched Azolla treatment was found equivalent to Fe‐EDTA and Fe‐EDDHA. This study is the first step in our research program aimed to establish the application of Fe‐enriched Azolla as a bioagent for the benefit of Fe‐deficient crops.     

A disposable system for soil pore‐water extraction by centrifugation

Abstract

Evaluation of the partitioning of contaminant and nutrient elements between soil particles and their surrounding solution requires separation of the pore‐water from the solids. Disposable soil‐sample holders are described that can be used in low‐ and ultra‐speed centrifuges. The pore‐water sample is filtered of paniculate during centrifugation, thus eliminating the tedious step of separating the centrifugate from the soil using pipettes. The system is inexpensive, works for both fine mineral and peat soils, requires little preparation time and provides enough pore‐water of sufficient quality for chemical analysis.     

A simple manual method for the determination of phosphate‐extractable (ion‐exchange membrane) sulphate in soils

Abstract

A simple manual method for measuring phosphate‐extractable sulphate in soils using basic laboratory equipment is described. Sulphate is extracted by a phosphated anion‐exchange membrane which, after elution, is measured turbidimetrically as barium sulphate. The results obtained by the proposed manual method compare well with a continuous flow analyser method using a range of Pacific Island soils.     

A simple non‐atomic absorption procedure for determining the effective cation exchange capacity of tropical soils

Abstract

A simple non‐atomic absorption procedure for determining the effective cation exchange capacity of tropical soils has been developed. The method involves the shaking of soil samples (10g) with ammonium chloride (3 x 25 cm³, 1 mol/L) to displace the exchangeable cations. The soil is then equilibrated with dilute ammonium chloride (3 x 25 cm³, 0.01 mol/L). After the final equilibration the ammonium ions retained by the soil are determined to facilitate the calculation of the ECEC. Data obtained for 22 tropical soils ranging in ECEC values from 1–50 cmol(+)/kg show a highly significant correlation with values derived using the compulsive exchange or summation procedures. The silver thiourea procedure data gave significantly poorer correlations with that obtained using all three of the above methods.     

Agrotool — A system for crop simulation

A system for simulation of crop dynamics is described. It includes a dynamic crop model for several cultures and a model shell. The model permits to simulate crop dynamics on the second level of plant productivity. The model shell serves for organization and implementation of series of computer experiments in dialogue regime. As it is known, soil and climatic conditions in the majority of Russia's regions differ from that in West Europe in a principal way. It especially concerns the continental Russia regions where deep droughts regularly occur, or Northwest regions, which are subjected to excess of water. So a special attention in model development was paid on account of the influence of water stress on plant production process.     

Heavy‐metal toxicity in plants 1. A crisis in embryo

Abstract

Heavy metals are often added indiscriminantly to soils in pesticides, fertilizers, manures, sewage sludges, and mine wastes, causing an imbalance in nutrient elements in soils. Heavy‐metal toxicity causes plant stress in various degrees dependent on the tolerance of the plant to a specific heavy metal. The objectives of this study were (i) to show that plant species and soils respond differently to heavy metals and (ii) to show the necessity for proper quantity and balance of heavy metals in soils for plant growth.

Three Fe‐inefficient and three Fe‐efficient selections of soybean, corn, and tomato were grown on two alkaline soils with Cu and Zn ranging from 14 to 340 and Mn from 20 to 480 kg/ha. Heavy‐metal toxicity caused Fe deficiency to develop in these plants. The Fe‐inefficient T3238fer tomato and ys₁/ys₁ corn developed Fe deficiency on all treatments and both soils. T3238FER tomato (Fe‐efficient) did not develop heavy metal toxicity symptoms on any treatment or soil. The soybean varieties and WF9 corn were intermediate in their response.

The unpredictable response of both the soil and the plant to heavy metals make general recommendations difficult. In order to maintain highly productive soils, we need to know what we are adding to soils and the consequences. Without some control, the continued addition of heavy metals to soils is a crisis in embryo.     

A simple “equal area” calibration for fisheye photography

A simple calibration method for fisheye lenses is described, which is suitable for lenses designed to produce image areas proportional to subtended solid angle. As examples, the method is applied to calibrate Canon, Nikon and Sigma fisheye lenses.     

Nutrient‐solution techniques for evaluation of iron efficiency of soybean 1

Abstract

The iron (Fe) efficiency of soybean [Glycine max (L.) Merr.] genotypes generally has been evaluated in the field on calcareous soil. A nutrient‐solution system has been developed to permit evaluation of Fe efficiency throughout the year. The objectives of this study were to assess the effectiveness of nutrient‐solution tests for evaluating the Fe efficiency of soybean genotypes and to evaluate alternative nutrient‐solution techniques that could minimize the cost of labor and chemicals. Five bicarbonate (HCO₃ ^‐) concentrations and three solution‐change schedules were evaluated in a factorial arrangement. Eight soybean genotypes with a wide range of Fe efficiency were evaluated in each treatment and in replicated field tests on calcereous soil during 3 years. Rank correlation coefficients between mean chlorosis scores of genotypes in nutrient solution and field tests ranged from 0.81 to 0.91 for the three solution‐change schedules and from 0.85 to 0.89 for the five HCO₃ ^‐ concentrations. Replacing the solution every 4 d was not superior to replacing it only at each stage of plant development or not changing the solution throughout the test. A stepwise increase in HCO₃ ^‐ level at each stage of plant development was not superior to utilizing a constant level of HCO₃ ^‐ throughout the test. The most economical evaluation of the Fe efficiency of soybean genotypes in nutrient solution can be achieved with no change in the solution and one or more HCO₃ ^‐ levels that are held constant throughout the test.     

A simple method for determination of ammonium in semimicro‐Kjeldahl analysis of soils and plant materials using a block digester

Abstract

A simple method for determination of ammonium in semimicro‐Kjeldahl analysis of soils and plant materials using a Tecator or Technicon 40‐tube block digester is described. It involves use of an inexpensive steam distillation apparatus that permits direct distillation of ammonium from the tubes used for Kjeldahl digestion in 40‐tube block digesters. The method is rapid and precise, and it gives results that agree closely with those obtained by the customary method of ammonium N analysis involving transfer of the Kjeldahl digest before distillation.     

Establishment of soil solution P levels for studies involving vesicular‐arbuscular mycorrhizal symbiosis

Abstract

A phosphorus sorption curve was developed to evaluate the influence of established levels of soil solution P on the development of vesicular‐arbuscular mycorrhizal (VAM) activity in Leucaena leucocephala (Lam.) de Wit grown on soil:sand mixture. The P sorption curve developed after nutrient amendment and wetting and drying treatments in the greenhouse predicted levels of P established in the soil solution more accurately than P sorption isotherm developed in the laboratory.

VAM activity measured in terms of P content of pinnules of Leucaena was significantly higher at lower soil solution P levels (0.01 and 0.02 mg/L) than at higher levels. In general, VAM activity declined after reaching a peak value at 30 days after planting (DAP).

Soil solution P levels monitored during the course of the experiment indicated that low initial P levels (0.01 and 0.02 mg/L) were readily maintained than higher ones. The proposed approach is thus appropriate for establishing soil solution P levels that permit optimal VAM activity.     

A micro‐pipette method for water dispersible clay

Abstract

The clay percentage determined by mechanical means in distilled water without the removal of organic matter and soluble salts and use of a chemical dispersant, is referred to as water dispersible clay (WDC). In this study, a “micro‐pipette” WDC method is developed and described. The method increases laboratory production, i.e., number of samples per day, and yet requires less laboratory space and time. In addition, this method yields, for most soils, WDC values comparable to those values obtained by the standard SCS “macro‐pipette” method. Statistical analysis of variance (ANOVA) for determination of WDC percent indicates nonsignificant effects at α = 0.05 for both method and method times soil but significant effects for method times soil interaction term at α=0.10. In order to characterize the particle‐size distributions, a moment analysis was run on each of the 14 soils. In this study, the distributions of most soils measured by the “macro‐pipette” method are not significantly different by the “micro‐pipette” method. This abbreviated method may represent a significant savings for both high‐volume characterization laboratories and research and developmental work. This application of the measurement of WDC may also be modified for use in the soil survey field office.     

A quick test procedure for soil nitrate‐nitrogen

Abstract

A procedure for extraction and measurement of nitrate‐nitrogen (NO₃‐N) in soil is described. Extracting solution [0.025M Al₂(SO₄)₃] and field‐moist soil are measured volumetrically, with NO₃‐N concentration measured by nitrate‐sensitive colorometric test strips or nitrate‐selective electrode. Across a range of soil texture, moisture content, and NO₃‐N concentration, the procedure was well correlated with conventional laboratory analysis of 2N KC1 soil extracts (r² = 0.94). This quick test procedure is proposed as an on‐farm monitoring technique to improve N management.     

Distillation solution with and without indicator for nitrogen‐15 measurement by optical emission spectrometry

Abstract

Optical emission spectroscopy provides a rapid and precise method for determining ¹⁵N/¹⁴N ratios of ¹⁵N‐enriched plant and/or soil samples. The objective of this study was to determine the effect of an indicator added in the distillation solution on the success rate of tube lighting in the optical emission spectrometer over a large range of N concentration in ¹⁵N enriched plant samples. One‐hundred‐eighty plant samples with large ranges of N concentration (4 to 30 g.kg^‐1 dry weight) and ¹⁵N atom enrichment (0.368 to 1.635%) were analyzed. Our data suggest that there was no difference in the success rate of tube lighting in emission spectroscopy and in ¹⁵N/¹⁴N ratio measured between samples prepared with and without addition of indicator in the distillation solution.     

A rapid petiole sap nitrate‐nitrogen test for potatoes

Abstract

A rapid test for measuring petiole sap nitrate‐N in potatoes was developed using a pH/ISE meter equipped with a nitrate‐ion specific electrode. Nitrate‐N measurements were made on fresh sap that was diluted with a solution of 0.075M Al₂(SO₄)₃‐18H₂O and 0.02M H₃BO₃. The sap nitrate‐N concentration, as determined by the rapid test, was highly correlated (r = 0.91, P<0.01) with dry matter nitrate‐N. Because of the non‐clogging design properties of the electrode used, this test procedure produced rapid and reliable results with good instrument stability and long electrode life. The chemicals used for this test are relatively non‐hazardous and the required tools can be assembled into a small portable kit. When properly calibrated, this test will provide added impetus to growers to rely on tissue analysis for corrective in‐season nitrogen (N) fertilization of potatoes.     

A greenhouse technique for screening Trifolium seedlings for iron‐deficiency chlorosis 1

Susceptible Trifolium plants often exhibit symptoms of iron (Fe)‐deficiency chlorosis when grown on high pH, calcareous soils. A greenhouse method was developed to screen seedlings for Fe‐deficiency chlorosis. ‘Yuchi’ arrowleaf (T. vesiculosum Savi.) and ‘Dixie’ crimson (I. incarnatum L.) clover seedlings were grown in “Super Cell”; Cone‐tainers in six calcareous Texas soils differing in Fe and selected other chemical characteristics. At the fourth trifoliolate leaf stage, chlorosis was induced by saturating the soil for a minimum of 2 weeks. The soils differed in their capacity to induce chlorosis in both clovers. Yuchi was more susceptible than Dixie, showing a higher percentage of chlorosis in five of the six soils. The results indicate that this screening method would be a useful tool for studying Fe‐deficiency chlorosis in Trifolium spp.     

Possibilities and limitations of utilizing 28Mg for studying Mg‐specific problems in higher plants

The possibility of utilizing artifical radionuclides in agricultural biological research enabled studies to be implemented in which the detection sensitivity of the nutrients to be investigated was one to two powers of ten higher than with physicochemical methods. Although usable radionuclides are available for numerous plant nutrients, their radiochemical properties partly restrict their utilization. For example, the relatively short half‐life of ²⁸Mg of 21.3 hours only permits short‐term studies. This is all the more disadvantageous the lower the specific activity of ²⁸Mg is. The ²⁸Mg produced from a lithium target in the experimental reactor Merlin at the KFA Jülich achieves a maximum specific activity of 1 mCi/g Mg. In contrast, specific activities of over 1 Ci/g Mg are achieved in the isochronous cyclotron where ²⁸Mg is generated from an aluminium target. This more or less carrier‐free ²⁸Mg is especially suitable for short‐term studies (minutes or hours) or for problem areas in which the ²⁸Mg uptake rates are very low. It was able to be demonstrated on the basis of autoradiographs that Mg is a relatively mobile nutrient in higher plants and is transported both in the xylem and also in the phloem. Its uptake and transport rate does not only depend on the presence and concentration of competing cations but is also considerably influenced by the type of plant and its nutritional status, especially by its K content. In studies on strawberry plants and grapevines it was demonstrated that the transport rate of Mg in the fruits was in part considerably greater than that of Ca. However, this relative preference for Mg in comparison to Ca largely depends in the case of grapevines on the uptake conditions and the type of application (dipping or trough application). In comparative studies of the leaf uptake of ²⁸Mg it was established that considerably more ²⁸Mg was taken up from ²⁸MgCl₂ than from a complete nutrient solution or leaf dressing solution.     

Determination of nitrate‐n in plants by an improved extraction procedure adapted for ultraviolet spectrophotometry

Abstract

An analytical procedure for the ultraviolet spectrophoto‐metric determination of nitrate‐N in plant material over the range 8–15 000 mg kg^‐1 is described. Plant material is extracted with 0.025 M Al₂(SO₄)₃ and oxidised activated charcoal and after filtering, the extract is treated with the same amount of oxidised activated charcoal. Correction for interfering organic ions which remain after treatment, is made by adjusting the absorbance at 225 nm by an estimate of the background interference determined from the absorbance value at 255 nm. The net absorbance at 225 nm is used to determine nitrate‐N concentration.     

Substitutes for benzidine as H‐donors in the peroxidase assay,for rapid diagnosis of iron deficiency in plants

Abstract

3,3'5,5’ Tetramethyl benzidine, 3‐Amino‐9‐ethylcarbazol and chlorpromazine are suggested as alternatives for benzidine as H‐donors in the peroxidase assay for diagnosing iron deficiency in plant leaves. Procedures with these reagents, which have been used successfully with citrus and other plants, are described.