Phosphorous levels on the ability of an iron‐inefficient and an iron‐efficient corn inbred to take up iron from nutrient solution

Abstract

The Fe‐inefficient corn (Zea mays L.) inbred Ys₁/YS₁ was compared with the Fe‐efflcient WF9 inbred for ability to take up Fe from solution culture at different P levels. A high level of P depressed Fe uptake more in the Ys₁/Ys₁ than in the WF9 inbred. The Ys₁/Ys₁ roots were high in P.     

Root and rhizosphere responses of iron‐efficient or ‐inefficient apple genotypes to solution pH

Solution culture with four pH levels was employed in this experiment to evaluate root and rhizosphere responses of Malus xiaojinensis [iron (Fe)‐efficient species] and M. baccata (Fe‐inefficient species) in order to pursue some of their physiological mechanism for Fe absorption. The results showed that M. xiaojinensis had a higher fresh weight per seedling than M. baccata at any of the solution pH levels tested and the differences were significant between the two species with increasing of the solution pH levels, particularly at the pH of 7.4 or 8.4. The reducing abilities of root exudates for the two species under test were decreased with increasing of the solution pH from 5.4 to 8.4, in which the reducing abilities for M. xiaojinensis were always more than two times higher than those for M baccata. The significant decrease of the reducing ability was found only at pH of 8.4 for M. xiaojinensis or at both 7.4 and 8.4 for M. baccata, respectively. Malus xiaojinensis had significantly higher respiration rates than M. baccata at the higher solution pH levels. Both rhizosphere pH and rhizosphere redox potential were influenced by the solution pH levels remarkably in distances of 0–4 mm to root surface or in distances of 5–10 mm along the root from the root tip, respectively. Genotypic differences in these two parameters were clearly showed at the solution pH of 7.4, in which rhizosphere pH of M xiaojinensis was clearly lower than that of M. baccata, while the rhizosphere redox potential of the former was much higher than that of the latter.     

Efficacy of commercial Fe(III)‐EDDHA and Fe(III)‐EDDHMA chelates to supply iron to sunflower and corn seedlings

Use of synthetic iron (Fe) chelates is the most common and effective way to treat Fe chlorosis in plants. Most commercial products contain Fe‐EDDHA or Fe‐EDDHMA but their efficacy can be quite different. Commercial products with EDDHA or EDDHMA as active components were chosen based on the data obtained by Lucena et al. (1992) in their chemical test. The chelates present extreme differences in behavior in the mentioned chemical tests. The analysis of the products revealed that the total Fe concentration is greater than the one indicated by the manufacturer in spite of a lesser amount of FeY^‐ present. The plant response to these commercial products was tested using short‐term greenhouse hydroponic cultures. Sunflower and corn were chosen because of their different behavior under Fe‐stress conditions. No significant difference between plants treated with Fe‐EDDHA or Fe‐EDDHMA chelates were observed. Since the purity index indicates there are too many differences between commercial formulations of the same type of chelate, the differentiation between groups cannot be determined with commercial products. Index I3, described by Lucena et al. (1992), does not correlate with the plant response because it did not consider the purity percentage of the products.     

Pattern of iron distribution in the soil‐plant system and its possible relation to iron‐chlorosis

Abstract

The frequent concentration‐ranges of various nutrient elements in soils and in plants are compared. Iron is different from almost all other nutrient elements in the fact that its optimal concentration range in plants is much lower than its frequent concentration range in soils. It is suggested that this observation is related to a chemical‐physiological mechanism of control on the uptake of iron by plants which in turn may explain the situations in which iron deficiency conditions in plants arise.     

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.     

Tumorous crown gall response to iron‐deficiency stress in Fe‐efficient T3238fer and Fe‐inefficeent T3238fer tomatoes

Abstract

Although sunflower (Helianthus annus L.) is an Fe efficient plant, tumorous crown gall tissue development and tissue ability to reduce Fe³⁺ to Fe²⁺ were both diminished by Fe‐deficiency stress. Crown gall also develops readily on Fe‐efficient and Fe‐inefficient tomato cultivars (Lycopersicon esculentum Mill.). The objective of this study was to determine if the effect of a limited Fe supply on the growth, nutrition and reduction of Fe³⁺ to Fe²⁺ by tumorous crown gall would differ between Fe‐efficient T3238FER and Fe‐inefficient T3238fer tomato. Healthy green 25‐day‐old plants were either stem‐inoculated with Agrobacterium tumefaciens to induce tumorous crown gall tissue development or were left uninoculated for comparison. Plants were grown in modified Hoagland nutrient solutions containing 0.0, 0.15, 0.6 and 2.0 mg Fe L^?1. Yield of tumorous crown gall tissue was not diminished by low solution Fe in T3238FER, but was in T3238fer. This was attributed to inability of the T3238fer tomato to make Fe available to itself. Tumor tissue from both cultivars contained more Fe, Cu and P than normal stem tissues, which confirms a modified metabolism in these tissues previously observed in sunflower. An abundant supply of Fe enhances the development and growth of the tumorous crown gall tissue, but a deficient supply of Fe retards its growth.     

Response of wheat cultivars to different soil nitrogen and moisture regimes: II. Nitrogen up‐take,partitioning and influx 1

Nitrogen (N) is one of the major mineral nutrients required for growth and development of plants. Soil water availability, N concentration at the root surface and the ability of plants to absorb N are the most important factors that affect N uptake and partitioning. The objective of this study was to use greenhouse and growth chamber environments to investigate how two contrasting water regimes (stress and nonstress) and different soil N concentrations affect the uptake and distribution of N among different plant parts of three cultivars of wheat (Triticum aestivum L.) at different stages of development Results showed that at the beginning of stem elongation and under non N limiting conditions, there was a high and positive correlation between shoot dry matter production and shoot N content. Under N deficient soils that received different N rates, shoot N content was more related to shoot N concentration than to dry matter. Root growth and N content of the ‘Saada’ cultivar were negatively affected by high soil N concentration. Under mild water stress or nonstressed conditions, N uptake by the shoot increased with increased soil N in all cultivars. Overall, severe water stress masked the effect of N supply, and decreased N uptake in the case of ‘Merchouch 8’ and ‘Saada’. Root N content was not affected by water stress but increased when N was supplied. At anthesis and after rewatering plants from boot stage to anthesis, the plants fully recovered, and those that were water stressed, increased their N absorption to a rate much higher than those that were stressed. Nitrogen influx (NI) decreased with water stress, but increased more with increased soil N under well watered conditions than under stress. “Merchouch 8’ had higher NI than ‘Saada’. From this study we can conclude that the effect of N supply on N content was masked by severe water stress, and ‘Nesma’ was less sensitive to this stress. At anthesis, plants that were previously water stressed increased their rate of N uptake during the recovery. Root N was not affected by water stress but increased when soil N was increased.     

Comparative response of corn and soybean to seed‐placed phosphorus over a range of soil test phosphorus

Abstract

The responses of corn and soybean to seed‐placed fertilizer were compared over NaHCO₃‐extractable soil phosphorus (P) levels ranging from 3 to 35 ppm in a two‐year experiment. Early season corn and soybean shoot‐P concentrations were increased with increasing soil test P and were increased with seed‐placed P regardless of soil test P, although the increases were greater for corn than soybean. Corn grain yield increased with increasing soil test P to a plateau level and increased with seed‐placed P regardless of soil test P. A side‐band (5 cm × 5 cm) application of 39 kg P ha^‐1 at a low soil test P increased yield more (P<0.15) than application of 7 kg P ha^‐1 with the seed. A side‐band application of 9 kg P ha^‐1 at a medium soil P test did not increase yield. Soybean yield was increased with increasing soil test P one year out of two, but did not respond to seed‐placed P in either year. The yield response of corn was attributed to the increased P concentration prior to the 6‐leaf stage.     

Variation of early growth and nutrient content of no‐till corn and soybean in relation to soil phosphorus and potassium supplies

Abstract

Knowledge of relationships between variation in early plant growth and soil nutrient supply is needed for effective site‐specific management of no‐till fields. This study assessed relationships between soil test phosphorus (STP) and potassium (STK) with early plant growth and P or K content of young corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] plants in eight no‐till fields. Composite soil (0–15 cm depth) and plant (V5‐V6 growth stages) samples were collected from 400‐m² areas at the center of 0.14‐ha cells of a 16‐cell square grid and from 2‐m² areas spaced 3 m along each of two 150‐m intersecting transects. Correlation, regression, multivariate factor analyses were used to study the relationships between the variables. Variability was higher for samples collected from the transects. Plant dry weight (DW), P uptake (PU), and K uptake (KU) usually were correlated with STP and STK but the correlations varied markedly among fields. Relationships between soil and plant variables could not always be explained by known nutrient sufficiency levels for grain production. Plant P concentration (PC) was not always correlated with STP and sometimes it increased linearly with STP, but other times increased curvilinearly until a maximum was reached. Plant K concentration (KC) usually was correlated with STK, however, and increased linearly with increasing STK even in fields with above‐optimum STK. The results suggest greater susceptibility of early growth to STP than to STK and greater plant capacity to accumulate K compared with P over a wide range of soil nutrient supplies. Variation in STK likely is a major direct cause of variation in KC over a wide range of conditions but variation in STP is not likely a major direct cause of variation in PC when high STP predominates.     

Availability of cobalt‐60 to corn and bean seedlings as influenced by soil type,lime, and DTPA

Abstract

Uptake of Co by corn (Zea mays) and bush beans (Phaseolus vulgaris) seedlings was affected by plant species, soil type and soil amendment. Bean leaves preferentially accumulated ⁶⁰Co in comparison with corn leaves. Both the DTPA and (lime and DTPA) treatments enhanced ⁶⁰Co uptake by both plant species, notably in the Troup soil which had lower cation exchange capacity (CEC) and lower soil fertility in comparison with Dothan soil. Conversely, soils with lime but without the chelating agent suppressed ⁶⁰Co uptake. This dictates that farming practices should be closely evaluated if crops for livestock and human consumption are to be raised in fields contaminated by radionuclides.     

Leachability and distribution of zinc applied to an acid soil as controlled‐release zinc chelates

Abstract

Fertilizers that contain zinc (Zn)‐EDTA and Zn‐lignosulfonate (Zn‐LS), which can also be coated with rosin, were placed at the top of columns of an acid Calcic Palexeralf soil which were periodically irrigated. The liberated Zn remained mostly on the top of the column when the source of Zn was Zn‐LS but Zn migrated through the column when Zn‐EDTA was applied. The use of a coating on the Zn‐EDTA fertilizer diminished the loss of Zn by leaching from 52% to 20% at the end of the experiment at the highest coating percentage (36%). The distribution of the Zn in the soils was studied by fractionation and showed that added Zn remained in the soils in more favorable forms for uptake by plants in comparison with the control soil. The labile fraction (F1) and especially that organically complexed increased, and the percentage corresponding to the residual fraction that was 89% in the native soil diminished in all cases being in the most favorable case by 25%. Correlations between the extracted fractions (r=0.57–0.99, P<0.01%) showed that, in general, a dynamic equilibrium existed between them. The DTPA‐extractable Zn also correlated positively with the most labile Zn fractions, although the significance level depended on the depth.     

Use of NH4 HCO3‐DTPA soil test to assess availability and toxicity of selenium to alfalfa plants

Abstract

This study was carried out to determine if ammonium bicarbonate‐DTPA soil test (AB‐DTPA) of Soltanpour and Schwab for simultaneous extraction of P, K, Zn, Fe, Cu and Mn can be used to determine the availability index for Se. Five Mollisols from North Dakota were treated with sodium selenate and were subjected to several wetting and drying cycles. These soils were extracted with hot water and with ammonium bicarbonate‐DTPA (AB‐DTPA) solution for Se analysis. Alfalfa plants were grown in these soils in a growth chamber to determine plant uptake of Se. In addition to the above experiment, coal mine soil and overburden materials from Western Colorado were extracted and analyzed as mentioned above.

It was found that hot water and AB‐DTPA extracted approximately equal amounts of Se from Mollisols. A high degree of correlation (r =0.96) was found between Se uptake by plants and AB‐DTPA extractable Se. Extractable level of Se in treated soils was decreased with time due to change of selenate to less soluble Se forms and plant uptake of Se. An AB‐DTPA extractable Se level of over 100 ppb produced alfalfa plants containing 5 ppm or higher levels of Se that can be considered toxic to animals. Soils with about 2000 ppb of extractable Se were highly toxic to alfalfa plants and resulted in plant concentrations of over 1000 ppm of Se. The high rate of selenate (4ppm Se) was less toxic to alfalfa plants in soils of high organic matter content. This lower toxicity was accompanied with lower extractable levels of Se.

The AB‐DTPA solution extracted on the average about 31% more Se than hot water from the mine and overburden samples and was highly correlated with the latter (r =0.92). The results indicated the presence of bicarbonate‐exchangeable Se in these materials.     

The comparative plant availability of 32P myo‐inositol hexaphospha.te and KH2 32PO4 added to soils

Abstract

The comparative availability to Lolivm perenne of ³²P myo‐inositol hexaphosphate (IH³²P) and KH₂ ³²PO. added to soil could be determined unequivocally from the ³²P count of leaf material even when dry matter yields and total P content were not significantly different from the control.

IH³²P was equivalent to KH₂ ³²PO₄. in a soil with a low P retention at 200 p.p.m. P but not at 20 p.p.m. P. IH ³²P was totally unavailable in two soils with high P retention at 200 p.p.m. and 20 p.p.m. P, whereas uptake of KH₂ ³²PO₄. was observed in each instance.