Monopotassium phosphate as a phosphorus and potassium source for greenhouse‐winter‐grown cucumber and muskmelon 1

Glasshouse experiments were conducted at the Newe Ya'ar Research Center in the winter seasons of 1992/93 and 1993/94 to examine a phosphorus/ potassium (PK) fertilizer for cucurbit crops. Monopotassium phosphate [(MKP), KH₂PO₄] was found to be very effective as a P and K source for cucumber (Cucumis sativus L.) and muskmelon (Cucumis melo L.) plants grown in soilless container conditions. The efficiency of MKP was essentially not different from that of the combination of phosphoric acid (H₃PO₄) and potassium chloride (KCl) which is widely used in the commercial production of vegetables. Appropriate fertilization of cucumbers with MKP in 1992/93 affected late‐season yield more than early‐season yield. Deficiency of P and K in Gala muskmelon inhibited vegetative growth and decreased yield. The reduced yield resulted from both less fruit‐setting and smaller fruit size. The MKP rates required by cucumber plants in 1993/94 depended primarily on growth medium composition. Generally, plants grown in inert tuff (volcanic gravel) and sandy media responded more significantly to MKP than did those grown in media rich in organic matter. There are at least three reasons for preferring the use of MKP, first it is much safer to handle than is H₃PO₄, second it is highly soluble and can be easily incorporated in fertigation systems, and third it has a high PK content.     

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.     

Response of alfalfa to a phillipsite‐based slow‐release fertilizer

Abstract

A greenhouse experiment was conducted with alfalfa (Medicago sativa L. cv. Aragon wide leaf) to test the performance of a zeolite (phillipsite) phosphorus‐potassium (P‐K) fertilizer versus soluble potassium dihydrogen phosphate (KH₂PO₄) applied to a coarse‐textured substratum consisting of a mixture 1: 4 (in volume) soihbasaltic ash. Plants were sown at four fertilization rates and five harvests were collected after nine months. The nutrient content in plant tissue was higher in the plants treated with zeolitic fertilizer, although the response was primarily due to P. No differences due to the fertilizer source were observed for dry matter yield. When considering nutrient uptake, differences between the two fertilizers were enhanced, although the results for P are more pronounced. The soil nutrient content found after the experiment shows that available P was significantly higher in those pots that received the zeolite fertilizer, but no differences were found for K.     

Iron deficiency studies of sugar beet using an improved sodium bicarbonate‐buffered hydroponic growth system

A sodium bicarbonate (NaHCO₃)‐buffered hydroponic growth system was developed that simulates alkaline soil growth conditions necessary to screen sugar beet genotypes for iron (Fe) efficiency character. Three genotypes (NB1, NB4, and F, hybrid, NB 1xNB4) with differing capacities for Strategy I Fe responses were phenotyped successfully using this system. Genotypes NB1 and NB1xNB4 are Fe efficient, while NB4 is Fe inefficient. It was demonstrated that 5 mM NaHCO₃ provided buffering within an optimal range (pH 7.3 ‐ pH 6.3) for the duration of ‐Fe treatments, promoted enhanced H⁺ extrusion, and increased the in vivo capacity for Fe³⁺‐chelate reduction (Fe³⁺‐chelate reductase [FCR] activity), especially in the roots of the Fe efficient genotypes. The same concentrations of NaHCO₃ did not interfere with Fe supply to +Fe control plants of any genotype. The in vivo capacity for Fe³⁺‐chelate reduction increased over fivefold in both Fe efficient genotypes (NB1 and NB 1xNB4), but just under twofold in the Fe inefficient genotype (NB4). Localization and duration of enhanced Fe³⁺‐chelate reduction capacity were dependent upon the Fe efficiency character of each genotype.     

A simple system for raising clean‐rooted plants for solution culture experiments

Abstract

A simple arrangement is described for growing seedlings with clean roots for use in solution culture experiments. It consists of a deep level tray containing seed trays subdivided into modules filled with smooth coarse gravel. These are flooded periodically with nutrient solution using a pump and time switch. The solution then drains back into a reservoir underneath the tray. The system requires very little attention and spinach plants grew better in gravel than in sand or commercial peat‐based compost.     

Nitrogen accumulation in nodulated and non‐nodulated pea plants,grown in a sandy soil at different acidities

Abstract

The growth of nitrate‐supplied and dinitrogen‐fixing pea plants was studied in a pot experiment with a sandy soil in a pH‐H_?O range from 3.4 to 5.6. Optimum growth in both treatments occurred at pH 5.0. At low pH, N₂‐plants yielded significantly less than NO₃‐plants. Planting of nodulated seedlings did not enhance yield in comparison with sowing in inoculated soil, indicating that nodulation was not the most sensitive process in restricting yield. Comparison of the nitrogen contents of shoots of planted and sown N₂‐plants allowed the suggestion that the synthesis of nitrogenous compounds was also not limiting yield. At low pH, root growth was severely reduced in dinitrogen‐fixing plants in comparison with nitrate‐supplied plants. This difference could be explained by the influence of the form of nitrogen nutrition on the cation‐anion uptake pattern of the plant and the resulting pH‐shift in the rhizosphere. It is to be expected that in an acid soil under field conditions the indirect effect of nitrate on root growth and nodulation via increase of the pH is more extensive than its direct negative effect on nodulation.     

Iron oxide as an iron source in potting‐soil mixtures

Abstract

A commercial product of Fe oxide‐metallic Fe at rates of 2 and 10 pounds per cubic yard (1.2 and 6 kg per cubic meter) in soil‐sawdust and soil‐bark mixtures was useful when Fe‐inefficient plants were grown in containers. A high Zn level in the Ys₁/Ys₁ Fe inefficient corn inbred (Zea mays L.) was associated with low Fe status. High Fe levels seemed to suppress Cd uptake.     

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.     

Iron chlorosis in macadamia as affected by phosphate‐iron interactions 1

Iron (Fe) chlorosis induced by heavy phosphate (P) fertilizations is a serious problem for macadamia (Macadamia integrifolia) in Hawaii. To address this problem, a study was conducted to quantify the effects of P‐Fe interaction on macadamia leaf composition and chlorosis. The soil used was a limed Oxisol (Tropeptic Eutrustox, Wahiawa Series), pH 5.5. Phosphate was added as treble superphosphate at 0, 150 and 500 mg P/kg. The 150 mg P/kg rate was designed to yield approximately 0.04 mg P/L in the soil solution, a level considered adequate for macadamia growth. The 500 mg P/kg rate was intended to produce approximately 0.2 mg P/L, a level required by many horticultural crops but considered excessive for macadamia. Iron was added as Fe‐DTPA at 0, 5 and 10 mg Fe/kg soil, and factorially imposed on the P treatments. Color Index, a numerical rating based on hue, value and chroma from a Munsell Color Chart for Plant Tissues, was correlated with leaf chlorophyll concentration and used as an indicator of chlorosis.

Phosphate concentrations in leaves increased with increasing P application rates as expected, but decreased remarkably with increasing Fe rates (at a constant P rate). Plant Fe unexpectedly remained unchanged with increasing Fe rates but decreased with increasing P rates. The results suggest that (1) soil‐solution Fe was not a limiting factor to macadamia growth as is often incorrectly assumed for high P‐fertilized soils, (2) Fe uptake was restricted not because soil‐solution Fe was low but because plant P was excessively high, and (3) Fe translocation from roots to leaves may have been hampered by high P in the plants. Consequently, Fe chlorosis was intensified primarily by P fertilization (actually, by high plant P concentrations) and secondarily by P‐Fe interactions. Chlorosis, as measured by Color Index, can be diagnosed by a leaf Fe/P ratio < 0.06, and predicted by a soil‐solution ³√Fe/P ratio < 15.     

Iron‐stress response of inoculated and non‐inoculated roots of an iron inefficient soybean cultivar in a split‐root system

The objective of this study was to establish whether the iron‐stress responses observed in T203 soybean (Fe‐inefficient) with active nodules are products of the nodules or of the entire root system. A split‐root system was used in which half the roots of each plant were inoculated and actively fixing nitrogen and the other half were not. Soybean cultivar T203 is normally Fe‐inefficient and does not exhibit the Fe‐stress responses, however an iron‐stress response did occur during active N₂ fixation in earlier studies. This implies that the active nodules influenced the plant's ability to respond to Fe‐deficiency stress. In this study, the Fe‐stress response (H⁺ and reductant release) observed in T203 soybean was limited to the inoculated side of the split‐root system. The severe Fe chlorosis which developed in these plants was overcome in a manner similar to Fe‐efficient cultivars undergoing normal Fe‐stress response and the T203 plants completely regreened. Exudation of H⁺ ions was similar in both the presence and absence of Fe, and was generally limited to inoculated roots. Reductant release was nearly nonexistent from the non‐inoculated roots and was greater for the Fe‐stressed (‐Fe) plants than for non‐stressed (+Fe) plants. Thus, the response observed, which alleviated Fe chlorosis, appeared to be associated with N₂ fixation of the active nodules.     

Control of arsenic toxicity in rice plants grown on an arsenic‐polluted paddy soil

Abstract

Paddy soils of over 500 hectares had been polluted by arsenic (As) from tailings at an abandoned lead‐zinc mine at Shaoxing, Zhejiang, China. Several field experiments were conducted to establish measures for reducing As toxicity to rice plants. The results obtained were as follows. Fresh Chinese milkvetch (Astragalus sinicus L.) was not supposed to be used as green manure in arsenic polluted paddy soils. Although liming (1,500 kg CaO hectare^‐1) could reduce water‐soluble As (H₂O‐As) in the soil, the rice plant grew badly. The treatments of FeCl₃ (25 mg Fe kg^‐1 soil) and MnO₂ (25 mg Mn kg^‐1 soil) could markedly lower the H₂O‐As and arsenite [As(III)] percentage in the soil and make the plant grow better than the control experiment (CK). Without adding any materials to the soil, wetting and drying (furrowing and draining) in the paddy soil could increase soil redox potential greatly and lower the H₂O‐As and As(III) percentage obviously leading to better rice growth. In addition, the As contents of roots, flag leaf, grain, and husked rice of 11 new cultivare of early rice were determined and correlation analysis was conducted. Uptake and accumulation of As in different parts of cultivars Zhefu‐802 and Erjiufeng at the 4 As levels of the paddy soil demonstrated that the As contents in husked rice of both cultivars exceeded the hygienic standard (0.7 mg As kg^‐1) when they grew in the paddy soil having total As content of about 70 mg kg^‐1 for Zhefu‐802 and 100 mg kg^‐1 for Erjiufeng, respectively.     

Zinc toxicity‐induced variation of mineral element composition in hydroponically grown bush bean plants

Bush bean plants (Phaseolus vulgaris L. cv Contender) were grown for twenty days in nutrient solution (pH=5), containing 0.13, 0.3, 0.5 or 0.75 mg 1^‐1 Zn as ZnSO₄‐7H₂O. The plant yield decreased linearly with the increase of the Zn concentration supplied. The phytotoxic threshold content (for 10% growth reduction) was about 486, 242, 95 and 134^‐ μg Zn g^‐1 for roots, steins, mature primary and trifoliate leaves, and developing leaves, respectively. High inverse correlation coefficients with the Zh concentration supplied were found for the Mn content of all organs, for the P content of roots, and for the Cu and Ca contents of developing leaves. Significant positive relations were found for the Fe, Zn and Cu contents in roots and for the Zn con‐ tents in stems and fully expanded leaves. The ratios of the mineral contents between organs suggest inhibition of uptake of Mn and P, and inhibition of translocation of Fe, Cu and Ca. The relation between dry weight decrease and Zn‐induced nutrient content disorders were discussed.     

Behavior of iron‐inefficient plants when grown in combinations of calcareous and noncalcareous soils

Abstract

When Fe‐inefficient plants were grown in mixtures of calcareous Hacienda loam soil and noncalcareous Yolo loam soil compared with plants grown in unmixed soils, characteristics and composition of the plants including Fe deficiency were generally intermediate to those with either soil alone. Noncalcareous soil adjacent to calcareous soil allowed PI 54619–5–1 soybeans (Glycine max L.) to obtain sufficient Fe.     

Water‐retention capability as a selection criteria for drought resistance in wheat

Four durum wheat cultlvars (Triticum turgidum spp. durum Desf.) from different countries of origin (Austria, Ethiopia, and Italy) were investigated. Plants were grown in pots under glasshouse conditions. Immediately after the full development of the flag leaves, these leaves were detached for the screening. Distinct differences in water‐retention capabilty among the cultivars was observed. The drought‐resistant (hardy) types, Valgerardo and Boohai, showed better water retention capabilty than the drought‐sensitive ones, such as DZ‐04–688. Poor yielding cultivars under field conditions were also found to be poor in water‐retention capability and vice versa. The applied method is simple and inexpensive. It adds another procedure when screening for drought resistance. However, it needs further confirmation by cultivars covering a broader range of genetic diversity.     

Use of a radio‐labelled chloric anion (36CLO3‐) as an analogue for tracking the nitrate (NO3‐) transport in higher plants

The suitability of the use of radio‐labelled chloric (³⁶ClO₃‐) as an analogue for tracing nitrate (NO₃ ^‐) uptake by intact plants was examined with regards to the possibly promising properties of the radioisotope for application in microautoradiographic studies. The identity of the electrolytically produced ³⁶ClO₃ ^‐ was checked by TLC autoradiography and radio high pressure liquid chromatography (HPLC). The experiments were carried out at the lower concentration range of NO₃‐ uptake with different plant species using double labelling with ³⁶ClO₃‐ and ¹³NO₃‐. The results demonstrate that the influx as well as the release from the labelled root system to exchange solutions differed markedly between the two tracers indicating a strong discrimination between ClO₃‐ and NO₃‐ ions. Thus, ³⁶ClO₃‐ labelling was considered to be inadequate for following the pathway of NO₃‐ across the root tissue by microautoradiographic methods.     

Soil and plant calibration for cucumbers grown in the mid‐Atlantic coastal plain

Abstract

Few soil test and plant tissue calibration data exist for cucumbers (Cucumis sativus L.). Two years of a singly‐replicated cucumber fertility study were conducted to develop soil and plant data for calibration purposes employing the Boundary Line Approach. Fertility treatments consisting of 4 K levels (as KC1), 3 Mg levels (as MgCl₂), 3 pH levels (as Calcitic limestone), and 4 N rates (as urea ammonium nitrate) were factorilly arranged and completely randomized to give 108 treatments in both 1987 and 1988. Analyses were performed upon leaf samples for N, P, K, Ca and Mg at early bloom and soil samples for Mehlich (M) 1‐ and 3‐ P, K, Ca and Mg, and pH. Cucumber yields were determined on early (two fruit pickings) and total (four fruit pickings) sampling periods. High‐yielding cucumbers were attained at soil K (Ml = 64 mg/kg) and Mg (Ml = 29 mg/kg) levels lower than currently recommended. No significant differences in correlation coefficients between either Mehlich (Ml, M3) extractant and cucumber leaf P, K, Ca and Mg concentrations were found. Co‐efficients of determination (R²) values for the relationships (in 1987, 1988) between Ml‐ and M3‐extractable P (0.53, 0.40), K (0.77, 0.64), Ca (0.81, 0.71) and Mg (0.89, 0.74) were all highly significant (P ≤ 0.01). No significant differences were noted between early and total high‐yielding cucumber leaf concentrations and ratios developed for use as preliminary sufficiency ranges and DRIS norms, respectively. A reevaluation of cucumber coastal plain soil test calibrations, especially with regard to K, appears necessary. This study provides further support for the conversion of Ml to M3 soil extraction methodology.     

Reduction of structural iron in selected iron‐bearing minerals by soybean root exudates grown in an in vitro geoponic system

Research on the reduction of iron (Fe) by plant‐root exudates has been conducted using hydroponic solutions containing Fe salts or chelates. These solutions, however, fail to reflect the true soil environment because plants derive their majority requirement from the solid Fe(III) sources. An in vitro Geoponic system (IVGS) is developed to study the reduction of Fe‐bearing clay minerals, i.e., Upton and SWa‐1 (smectite), and Si‐containing amorphous Fe oxide by soybean‐root exudates. Surface sterilized soybean seeds, [Glycine max (L.) Men.] cv. Williams (marginally susceptible to Fe chlorosis), were germinated in presterilized glass culture tubes containing semi‐solid agar media (sucrose free) and Fe minerals. These tubes were placed in an incubator programmed for a white‐fluorescent light cycle for 16 h and temperature setting of 25±2°C. After 15 d of plant growth, the system was analyzed for Fe²⁺ and total Fe. The amount of structural Fe reduction was 0.012, 0.095 and 0.182 mmol/g for Upton, SWa‐1, and Si‐containing amorphous Fe oxide samples, respectively. The reduction of structural Fe in the Fe containing minerals was likely caused by phenolic root exudates which oxidized to diquinones.     

Use of labeled sulphur‐35 for tracing sulphur transfers in developing pods of field‐grown oilseed rape

Abstract

This study was conducted to better understand the dynamics of sulphur (S) transfer between pod walls and seeds of field‐grown oilseed rape by using sulphur (³⁵S) as an investigative tool. Labeling experiments with ³⁵S were carried out to determine the effects of nitrogen (N) and sulphur fertilization on these transfer mechanisms. Sixty‐four plants from field trials fertilized with 200 kg N ha^‐1 in the forms of ammonium nitrate (AN) or urea (U), with or without 75 kg S ha^‐1 in the forms of ammonium thiosulphate and MgSO₄ were sampled. At 30, 43, 56, and 77 days after flowering (DAF), terminal racemes were cut and labeled with ³⁵S‐SO₄ ^2‐. After labeling, pods and seeds were separated into 3 groups according to their position on stem, and measurements of ³⁵S levels were performed accordingly. This short‐term labeling experiment showed that the pod walls retained from 39 to 61% of labeled ³⁵S, according to the different treatments, whereas seeds accumulated from only 1 to 16% of applied ³⁵S. On average, when S was added, a sharp decrease of ³⁵S in seeds from 2.6 to 1.7%, 9.0 to 5.4%, and 14.8 to 7.7% was observed at 30, 43, and 56 DAF, while progressively the percentage values in pod walls increased from 49.6 to 50.5%, 43.1 to 52.2%, and 41.7 to 63.5%, respectively. The increase of ³⁵S in pod walls was found to be tied to the glucosinolate concentration of seeds. By artificially increasing the ratio values of external N‐NO₃ ^‐ to S‐SO₄ ^2‐, these results demonstrated that the transfer of ³⁵S to seeds was more affected by the higher level of N‐NO₃ ^‐ in plant tissues than S‐SO₄ ^2‐ levels. The N/S ratio value above which the transfer of S was disrupted was around 6.     

Inoculation responses of perennial forage legumes grown in fresh hill‐land ultisols as affected by soil acidity‐related factors

A growth chamber experiment was initiated with two field moist, marginal and acidic (pH 5.1–5.2) soils of the Lily series (Typic Hapludults) in order to determine the need for improved legume‐rhizobia symbioses for forage species of current, or potential, use in the renovation of Appalachian hill‐land pastures. One soil was from an abandoned pasture having broomsedge (Andropogon virginicus L.) as the predominant vegetation, whereas the other was from a minimally‐managed pasture dominated by orchardgrass (Dactylis glomerata L.). Treatments included inoculation (or no inoculation) and the addition of aluminum, nil, or lime to provide a range of soil acidities. Both soils contained effective populations of naturalized rhizobia for white clover (Trifolium repens L.) and red clover (Trifolium pratense L.), but low and/or ineffective naturalized populations of rhizobia for alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), bigflower vetch (Vicia grandiflora Scop.), and flatpea (Lathyrus sylvestris L.). Seed inoculation, by lime‐pelleting, was highly beneficial in establishing effective symbioses for all these latter species. The addition of low levels of aluminum or lime (1.5 and 2.0 cmol/kg soil, respectively) had little effect on any of the symbioses, with the exception of those for alfalfa. Thus, an improved legume rhizobia symbiosis would not seem to be a prerequisite for renovating pastures established on chemically similar ultisols with the forage legume species examined in this study, especially if the pasture has at least some history of management.     

Loss‐on‐ignition as an estimator of soil organic carbon in a‐horizon forestry soils

Abstract

The determination of soil organic matter by wet digestion techniques is a slow and laborious analysis. Loss‐on‐ignition (LOI) provides a simple alternative technique for the estimation of soil organic carbon in non‐calcareous A horizon soils of the Natal midlands and Zululand forestry regions. Using multiple regressional techniques, the relationships between loss‐on‐ignition, Walkley organic carbon and soil texture for 55 soils were determined over a range of ignition temperatures. The relationships hold best for soil samples with relatively low organic carbon contents (< 5%). The optimum temperature for ignition was found to occur at 450°C and resulted in the relationship: Soil organic carbon = 0.284*LOI percent. No advantage is gained through ignition at higher temperatures due to the loss of clay mineral structural water, even if the soil texture is accurately known.