Leaf mineral element concentrations and growth of sweet sorghum subjected to acid soil stress

Abstract

The nutritional profile of sweet sorghum [Sorghum bicolor (L.) Moench] cultivars grown under acid soil field stress conditions is a critical consideration when developing plants which are adapted to these infertile soils. Uptake and accumulation of macro‐ and micronutrients vary among genotypes and ultimately Influence plant growth and development. This study compared fourteen sweet sorghum germplasm lines and varieties for their Individual patterns of leaf nutrient concentrations and productivity when grown under acid soil field conditions (pH 4.45 to pH 4.85) at three locations over a two‐year period. Significant year x location interactions were found for Fe, K, and Ca concentrations at both Blairsville and Calhoun and for Mn and P levels at Blairsville and Calhoun, respectively. Data from Calhoun on plant height, dry weight, visual stress ratings, and rainfall indicate a possible association between drought tolerance and acid soil tolerance in sorghum. No significant differences in A1 concentrations were found among these sweet sorghum lines and varieties, which indicate that their acid soil tolerance mechanisms are probably not related to A1. MN 1054 accumulated the highest levels of Mn in the three acid soils. The highest concentrations of Mg and P were found in Brandes. MN 960 had the highest visual stress ratings (highest susceptibility) while Brandes, Ramada, Roma, and Wray were the most tolerant. All fourteen cultivars apparently have some tolerance to acid soil stress conditions.     

Root reductant release as a measure of sorghum cultivar iron efficiency

Measurement of root reductant levels developed during plant Fe stress was tested as a possible assay for sorghum cultivar Fe‐efficiency screening. Iron‐stressed sorghum was shown to release reductants into CaCO₃ buffered nutrient solution; however, considerably more plants could be tested by extracting reductants from excised roots of Fe‐stressed sorghum in 35 ml of pH 3 nutrient solution and 1 mM glucose. An Fe‐efficient cultivar, RT×2536, and an Fe‐inefficient cultivar, BT×378, could be separated by measurement of reductants released into CaCO₃ buffered nutrient solution and by an excised root extraction method; however, neither method was as effective as visual rating methods.     

Leaf elemental concentrations and grain yield of sorghum grown on an acid soil

Abstract

Determination of the nutrient requirements of sorghum [Sorghum bicolor (L.) Moench] grown on acid soils is, a critical step in the development of plants which are adapted to these problem soils. Sorghum genotype, environment, and soil type interact with the uptake of elements and affect plant growth and production. This study compared the yields of a sorghum grain hybrid grown on a sandy loam soil at four acid pH levels. Nutrient concentrations in sorghum leaves on these soil regimes were also investigated. Grain yields declined 96% as soil pH decreased from 5.5 to 4.4. Leaf element analysis revealed that as pH decreased from 5.5 to 4.4, there was an increase in plant Al, Fe, Mn, K, P and a decrease in Cu, Zn, Mg, Ca. Interactions among several of these elements were readily apparent. Additional data involving different sorghum genotypes and different soil types are needed to establish a consistent pattern of element uptake on acid soils in relation to yield and plant production.     

The influence of NH4 +‐N vs. NO3 ‐‐n nutrition on root reductant release by fe‐stressed sorghum 1

The effect of NH₄ ⁺ ‐N on root reduction capacity developed during Fe stress was investigated in plants grown in a CaCO₃ buffered nutrient solution. After a 3‐day period of Fe stress, reduction capacity was not increased by the presence of NH₄ ⁺ ‐N in the growth medium or in the extracting solution. Since reductant degradation over time was pH dependent, experiments measuring root reductant release into nutrient solution would be confounded by treatments with different solution pH values. In an unbuffered nutrient solution a differential NH₄ ⁺ uptake due to the cultivar would affect solution pH and interfere with a reliable interpretation of reductant measurements.     

Nitrogen source and aluminum toxicity of two sorghum genotypes differing in aluminum susceptibility

After a 35 days growth on nutrient solutions with NO^‐ ₃ NH₄NO₃ and NH⁺ ₄ as nitrogen source (pH 4.2) dry matter yield of the sorghum genotype SC0283 was much less affected by Al (1.5 mg‐¹) than that of the genotype NB9040. With NO^‐ ₃ as the sole nitrogen source only growth of the NB9040 plants was significantly reduced. Since OH^‐ efflux, shoot Al content and concentrations of all major nutrients of both genotypes were almost equal, a higher sensitivity to Al may underlie the lower Al tolerance of the NB9040 genotype. In the presence of NH.‐N Al again lowered d.m. yield of the NB plants. With SCO283 significant Al effects on d.m. yield were observed only with NH₄NO₃. Aluminum drastically increased the amount of protons released per unit of root surface area, especially with the NB9040 line. This shift in proton flux density was partly the result of a decrease of the specific root surface area and partly due to enhanced excess of catlonic nutrients taken up. With NH₄NO₃‐fed plants the latter could almost completely be attributed to a changed N preference brought about by inhibited uptake of NO^‐ ₃ and a simultaneous enhanced NH, absorption. Although both proton efflux and NH⁺ ₄ preference of the NB plants were severely increased by Al, relative yields of this genotype were not lowered by NH⁺ _4. This can probably be explained by (1) the high NH, sensitivity of this cultivar through which Al effects can be masked and (2) the continuous adjustment of the solution pH through which rhizosphere conditions were prevented.     

Efficiency of nitrogen fertilization in sweet sorghum

Abstract

In spite of a high N requirement, sweet sorghum hasn't shown a consistent response to N fertilization. This research was designed to study the effect of N fertilization on sweet sorghum as affected by rates and time of N application. Five experiments were conducted under field conditions, where 0, 50, 100 and 150 kg N/ha were applied at sowing, and 35, 40, 55, 60 and 80 days after plant emergence. The soil had textures varying from sandy loam to clay, and organic matter contents from 0.67% to 1.9%. The highest yields were observed when N was applied early in the season, showing that for sweet sorghum, sidedressing with N is not necessary. All the N can be applied at planting time, which allows the highest fertilizer use efficiency. On the other hand, late applications of N fertilizer (after 40 days), when the floral primordia is already visible, has little effect on stalk or grain yield. In this situation, a double or triple rate had to be applied to overcome the low efficiency of N utilization. There was no great advantage in splitting the sidedressed N rate. On the other hand, it was impossible to link the response to N to soil analysis as performed in most of Brazilian laboratories.     

Soil temperature affects element uptake by sorghum

The influence of soil temperature on nutrient accumulation in aerial portions of sorghum plants was evaluated in a greenhouse experiment. Plants were grown in 20‐liter containers at cooled and ambient soil temperatures of 20 and 25C, respectively, and were harvested at the 8‐ and 12‐leaf stages of development for yield and nutrient analysis.

At the 8‐leaf stage, sorghum plants subjected to 25C were significantly higher in concentration of N, P, K, Mg, and Cu, but were significantly lower in Ca. Soil temperature did not significantly affect concentration of Zn, Fe, and Mn. At the 12‐leaf stage, sorghum plants grown in the warm soil temperature treatment were lower in concentration of N, K, Ca, Mg, Zn, Fe, Mn, and Cu than plants grown in the cooled‐soil treatment. Phosphorus showed a negative response to increased temperature.

It was concluded that further research relating element uptake and translocation to temperature is needed. Element accumulation in the roots, stems, leaves, and floral and seed portions of the plant should be included. In addition, the interaction between plant age and element concentration should be studied more thoroughly. Both this study and the published literature indicate that this interaction is significant for many of the elements.     

Evidence for the existence of different uptake mechanisms in soybean and sorghum for iron and manganese

A greenhouse experiment was conducted in which four varieties of soybean (Glycine max L.) and three varieties of sorghum (Sorghum bicolor L. Moench) were grown in a calcareous soil with and without soil applied FeEDDHA (0 and 2 mg Fe/kg soil). Soil applications of FeEDDHA increased Fe concentrations and reduced Mn concentrations in all varieties of soybean and eliminated Mn toxicity symptoms in Corsoy soybeans. Soil applications of FeEDDHA did not increase Fe uptake or affect Mn uptake into sorghum leaves. This study tends to support the hypothesis that there are distinct plant mechanisms between dicots and graminaceous species for the uptake of Fe, and that these mechanisms have a direct effect on Mn availability for plant uptake.     

Thermoelectric module cooling for photosynthesis chambers in plant nutrition studies 1

The water cooled system for controlling air temperature in photosynthesis assimilation chamber is cumbersome and requires a water tight system consisting of a double‐jacketed chamber. Manipulation of temperature control from one air temperature to another requires the adjustment of water bath temperatures. A simplified system for the air temperature control of the assimilation chamber and heat removal under high photon flux density would be desirable. An effective thermoelectric module cooling and heating system for a photosynthesis chamber was developed and evaluated for wheat (Triticum aestivum L.), sorghum [Sorghum bicolor (L.) Moench], and soybean [Glycine max (L.) Merr.] Air temperature variations within a chamber were maintained within 0.4°C, 0.9°C, and 0.3°C for the wheat, sorghum, and soybean chambers, respectively. The thermoelectric module system is simple and provides sufficient cooling and heating capacities to maintain chamber air temperature from 20°C to 30°C with 1100 μmol m^‐2 s^‐1 photon flux density for photosynthesis and dark respiration studies.

Air temperature within a photosynthesis chamber during photosynthesis in plant nutrition studies is one of the important environmental parameters that must be controlled. Due to excessive heat under the relatively high photon flux density used in photosynthesis measurements, air temperature has been traditionally cooled and controlled by passing chilled water through double walled water‐jacket chambers^{3,5,7,8,12,13}. Although the water cooled double‐jacket system has been successful in controlling temperature, maintaining water tight systems has been a problem. To alleviate some of the problems of a double‐jacketed system, air was cooled by passing over a water‐cooled radiator placed below the leaf^4,11 . Under conditions of relatively high photon flux densities (1100 ymol m^‐2 s^‐1), water‐cooled systems do not provide sufficient cooling capacity to maintain 25°C or less air temperature. Mauney, et al.⁶ reported photosynthetic data obtained from cuvettes that were electrically cooled by the Peltier device, but no details of the system were provided. In later studies^9,10,14, Peltier‐cooled systems appeared as a simple alternative to water‐cooled systems. This paper reports the details on an effective thermoelectric module cooling and heating system based on the Peltier principle for photosynthesis chambers.     

CALIBRATING CHLOROPHYLL METER (SPAD-502) READING BY SPECIFIC LEAF AREA FOR ESTIMATING LEAF NITROGEN CONCENTRATION IN SWEET SORGHUM

The chlorophyll meter (SPAD-502) is used to estimate nitrogen status of various crops. However, the relationship between SPAD readings and leaf nitrogen concentration (LNC) in sweet sorghum (Sorghum bicolor) has not been fully established. We examined the relationship between SPAD readings and LNC in sweet sorghum in a two-year study; and the effects of leaf thickness on the relationship was also examined. There was a significant relationship between the SPAD reading and LNC at each of two growth stages, but the correlation was weaker when the data for the two growth stages were pooled. This correlation improved when the specific leaf area was introduced as a second independent variable in the multiple regression analysis. This regression equation was applicable to not only different growth stages but also different seasons. The results suggest that the regression equation developed in this study can help in optimizing nitrogen fertilization for sweet sorghum production.