Differential Tolerances of Amaranthus Strains to High Levels of Aluminum and Manganese in Acid Soils

Species of Amaranthus are grown extensively as leafy green vegetables in tropical Africa and Asia and as high yielding grain crops in Western South America, Central America, Northern India, Western Nepal, and Pakistan. The crop is often grown on acid, marginal soils, under subsistence conditions, where liming even the soil plow layer may not be economically feasible. Hence, the identification or development of strains with high tolerance to acid soils would be beneficial. Aluminum and Mn toxicities are the most important growth‐limiting factors in many acid soils. The objective of our research was to determine the tolerances of selected Amaranthus strains to high levels of these elements in acid soils.

Fifteen strains, representing five species, were grown in greenhouse pots of an acid, Al‐toxic Tatum soil limed to pH 4.8 and 5.8. Strains differed significantly in tolerance to the acid soil. Relative yields (pH 4.8/pH 5.8%) ranged from 50.1 to 6.3% for tops and from 54.5 to 5.7% for roots. Four strains of A. tricolor L. (vegetable type) were significantly more tolerant than six strains of A. cruentus L. (seed and vegetable type). Strains of A. hypochondriacus L. and A. caudatus L. studied were intermediate in tolerance.

Twelve strains, representing four species, were grown on an acid, Mn‐toxic Zanesville soil at pH 4.6 and 6.3. Strains also differed significantly in tolerance to this acid soil; however, overall growth was better and strain differences were smaller than on Al‐toxic Tatum soil at pH 4.8. On Zanesville soil the relative top yields (pH 4.6/pH 6.3%) ranged from 74.1 to 18.6%. The most tolerant group included three strains of A. tricolor and one strain of A. hypochondriacus, but four strains of A. cruentus were also fairly tolerant. The sensitive end of the scale included one strain of A. cruentus and two strains of A. hypochondriacus.

In general, strains that were most tolerant to the Al‐toxic Tatum soil were also among the most tolerant to the Mn‐toxic Zanesville soil. Likewise, those most sensitive to the high Al soil were most sensitive to the high Mn soil. But some strains that were sensitive to excess Al in Tatum soil were fairly tolerant to high Mn in Zanesville soil.

Results suggest that superior strains of Amaranthus can be selected or developed for use on acid soils.     

Differential manganese tolerances of cotton genotypes in nutrient solution

Cotton genotypes [Gossypium hirsutum (L.)] C‐310–73,‐307 (307) and C‐Sgl, 70–517 (517), shown previously to differ in tolerance to an acid (pH 5.1), high manganese (Mn) Grenada soil from Arkansas, were grown in nutrient solutions containing variable concentrations of excess Mn to confirm and characterize their postulated differences in Mn tolerance. Based on crinkle leaf symptoms and leaf dry weights, the 307 genotype was significantly more tolerant than 517 to 4, 8, or 16 mg Mn/L at a maintained pH of 4.6 (Experiment 1) and also to 4 or 8 mg Mn/L at an initial pH of 5.0, not subsequently adjusted (Experiment 2). In Experiment 1, the relative leaf dry weight (wt. with no Mn/wt. with 8 mg Mn/L × 100) was 94% for genotype 307 and only 27% for 517. In Experiment 2, the corresponding relative leaf weights were 75% and 26% for 307 and 517, respectively. Plant analytical results indicated that the 307 genotype tolerates a higher concentration of Mn in its leaves than does 517. This failure to correlate Mn tolerance with Mn concentrations in plant shoots agrees with previous findings when these two genotypes were grown in acid Grenada soil. Iron (Fe) concentrations, Fe/Mn ratios, and magnesium (Mg) concentrations were higher in the Mn‐tolerant 307 than in the Mn‐sensitive 517, but concentrations of phosphorus (P), potassium (K), calcium (Ca), copper (Cu), and zinc (Zn) were not related to Mn tolerance. Because differential Mn tolerance in these two genotypes is associated with differential internal tolerance to excess Mn, rather than differential Mn uptake, studies are needed to determine the chemical forms of Mn in tolerant and sensitive plants whose leaves contain comparable concentrations of total Mn. Because both Mn and Fe (closely related elements in the Mn toxicity syndrome) have spin resonances, electron paramagnetic resonance (EPR) offers promise in attacking the problem of differential Mn tolerance in plants.     

Effect of manganese on concentrations of Zn,K, Ca and Mg in two bush bean cultivars grown in solution culture

Two bush bean cultivars [Phaseolus vulgaris L. cv. ‘Wonder Crop 2’ (WC‐2) and ‘Green Lord’ (GL)], differing in Mn toxicity, were grown in a growth chamber for 12 days in Hoagland No. 2 nutrient solution containing 0.05 to 1 ppm Mn as MnCl₂4H₂O with 1 ppm Fe as Fe‐EDTA, at an initial pH 5.00. Concentrations of Zn, K, Ca and Mg in the tissues of two bush bean cultivars were examined in relation to Mn toxicity.

The concentration of Zn in the leaves of Mn‐sensitive WC‐2 increased significantly with increasing Mn concentration in the solution, but such levels were not toxic to the plants.

The percent distribution of Zn and K in Mn‐sensitive WC‐2 plants (% of total uptake) significantly increased in the tops and decreased in the roots with increasing Mn concentration in the nutrient solution; however, Mn treatment had no effect on distribution of either Ca or Mg in WC‐2. External Mn concentration had little or no effect on the K, Ca, or Mg concentration in the tops of Mn‐tolerant GL.     

Acid soil tolerance of soybean (Glycine Max L. Merr.) germplasm from the USSR

Nineteen soybean genotypes (ten from the former USSR, two from Brazil and seven from USA) were tested for aluminum (Al) tolerance by growing them for 21 days in greenhouse pots of acid, Al‐toxic, unlimed Tatum (Typic Hapludult) subsoil at pH 4.0 and in limed subsoil at pH 5.1. Aluminum tolerance ranking depended upon the plant traits used in the screening process. Based on absolute dry shoot weights at pH 4.0, Giessener, Brunatna, and St.‐59 (USSR), and Biloxi (USA) were most tolerant; least tolerant entries included Yantarnaya and Smena (USSR), and Davis (USA). Based on relative shoot dry weights (pH 4.0/pH 5.1 %), Giessener, Brunatna, and St.‐59 (USSR) were among the most tolerant, Bossier, Biloxi, Essex, and Perry were intermediate, and Salute 216 (USSR), Chief (USA), and Santa Rosa and IAC‐9 (Brazil) were more sensitive to the acid soil. Based on absolute root dry weights, Giessener, and St.‐59 (USSR), and Biloxi (USA) were among the most tolerant and Smena, Yantarnaya and Salute 216 (USSR), and Chief (USA) were most sensitive. Based on relative root dry weights (pH 4.0/ pH 5.1 %), Giessener was most tolerant and Smena and Salute 216 least tolerant.

Preliminary evidence indicated that soybean entries screened for Al tolerance on acid Tatum soil also differed in tolerance to naturally occurring levels of ambient ozone in greenhouses at Beltsville. The Russian entries VNIIS‐2, Giessener, and Brunatna appeared more sensitive than USA entries Perry, Biloxi, Davis, and Bossier (USA), and Santa Rosa (Brazil). Aluminum tolerance and ozone tolerance appeared to coincide in the Perry genotype. Studies on Al‐ozone‐soybean genotype relationships are being continued at Beltsville.     

Tolerance of durum wheat lines to an acid,aluminum‐toxic subsoil

Durum wheat, Triticum durum Desf., is reportedly more sensitive to aluminum (Al) toxicity in acid soils than hexaploid wheat, Triticum aestivum L. em. Thell. Aluminum‐tolerant genotypes would permit more widespread use of this species where it is desired, but not grown, because of acid soil constraints. Durum wheat germplasm has not been adequately screened for acid soil (Al) tolerance. Fifteen lines of durum wheat were grown for 28 days in greenhouse pots of acid, Al‐toxic Tatum subsoil at pH 4.5, and non‐toxic soil at pH 6.0. Aluminum‐tolerant Atlas 66 and sensitive Scout 66 hexaploid wheats were also included as standards. Based on relative shoot and root dry weight (wt. at pH 4.5/wt. at pH 6.0 X 100), durum entries differed significantly in tolerance to the acid soil. Relative shoot dry weight alone was an acceptable indicator of acid soil tolerance. Relative dry weights ranged from 55.1 to 15.5% for shoots and from 107 to 15.8% for roots. Durum lines PI 195726 (Ethiopia) and PI 193922 (Brazil) were significantly more tolerant than all other entries, even the Al‐tolerant, hexaploid Atlas 66 standard. Hence, these two lines have potential for direct use on acid soils or as breeding materials for use in developing greater Al tolerance in durum wheat. Unexpectedly, the range of acid soil tolerance available in durum wheat appears comparable to that in the hexaploid species. Hence, additional screening of durum wheat germplasm for acid soil (Al) tolerance appears warranted. Durum lines showing least tolerance to the acid soil included PI 322716 (Mexico), PI 264991 (Greece), PI 478306 (Washington State, USA), and PI 345040 (Yugoslavia). The Al‐sensitive Scout 66 standard was as sensitive as the most sensitive durum lines. Concentrations of Al and phosphorus were significantly higher in shoots of acid soil sensitive than in those of tolerant lines, and these values exceeded those reported to cause Al and phosphorus (P) toxicities in wheat and barley.     

Variation of tolerance to manganese toxicity in Australian hexaploid wheat

High concentrations of manganese (Mn), iron (Fe), and aluminium (Al) induced in waterlogged acid soils are a potential constraint for growing sensitive wheat cultivars in waterlogged‐prone areas of Western Australian wheat‐belt. Tackling induced ion toxicities by a genetic approach requires a good understanding of the existing variability in ion toxicity tolerance of the current wheat germplasm. A bioassay for tolerance to high concentration of Mn in wheat was developed using Norquay (Mn‐tolerant), Columbus (Mn‐intolerant), and Cascades (moderately tolerant) as control genotypes and a range of MnCl₂ concentrations (2, 250, 500, 750, 1000, 2000, and 3000 μM Mn) at pH 4.8 in a nutrient solution. Increasing solution Mn concentration decreased shoot and root dry weight and intensified the development of toxicity symptoms more in the Mn‐intolerant cv. Columbus than in Norquay and Cascades. The genotypic discrimination based on relative shoot (54% to 79%) and root dry weight (17% to 76%), the development of toxicity symptoms (scores 2 to 4) and the shoot Mn concentration (1428 to 2960 mg kg^–1) was most pronounced at 750 μM Mn. Using this concentration to screen 60 Australian and 6 wheat genotypes from other sources, a wide variation in relative root dry weight (11% to 95%), relative shoot dry weight (31% to 91%), toxicity symptoms (1.5 to 4.5), and shoot Mn concentration (901 to 2695 mg kg^–1) were observed. Evidence suggests that Mn tolerance has been introduced into Australian wheat through CIMMYT germplasm having “LERMO‐ROJO” within their parentage, preserved either through a co‐tolerance to Mn deficiency or a process of passive selection for Mn tolerance. Cultivars Westonia and Krichauff expressed a high level of tolerance to both Mn toxicity and deficiency, whereas Trident and Janz (reputed to be tolerant to Mn deficiency) were intolerant to Mn toxicity, suggesting that tolerance to excess and shortage of Mn are different, but not mutually exclusive traits. The co‐tolerance for Mn and Al in ET8 (an Al‐tolerant near‐isogenic line) and the absence of Mn tolerance in BH1146 (an Al‐tolerant genotype from Brazil) limits the effectiveness of these indicator genotypes to environments where only one constraint is induced. Wide variation of Mn tolerance in Australian wheat cultivars will enable breeding genotypes for the genetic solution to the Mn toxicity problem.     

Differential tolerances of two old world bluestem genotypes to excess aluminum in acid soil and nutrient solution

Two genotypes of Old world bluestems from the species Bothriochloa intermedia (R. Br.), A. Camus, shown earlier to differ in tolerance to acid, Al‐toxic Tatum subsoil at pH 4.1, were characterized further with respect to growth in pots of Tatum soil over a wider pH range and tolerance to Al in nutrient solutions. The two genotypes studied were acid‐soil tolerant P. I. 300860 (860) and acid soil sensitive P. I. 300822 (822).

The soil experiment confirmed earlier rankings of acid soil tolerance in these two genotypes. For example, with 0, 375 or 750 ug CaCO₃ g^‐1 soil (final pH 4.0, 4.3 and 4.6), the 860 genotype produced significantly more dry top weight than 822, but these differences were precluded with 1500 or 3000 ug g^‐1 CaCO₃ added (pH 4.7 and 5.4). At pH 4.3 and 4.6, the root dry weights of the two genotypes were also significantly different and weights were equalized at pH 4.7 and 5.4. The 860 genotype made fairly good top growth (67% of maximum) at pH 4.3 and a soil Al saturation of 63%; this situation was lethal for 822. When grown in greenhouse pots, the acid‐soil tolerant 860 genotype required only about one fourth as much CaCO₃ as 822 to produce good growth of forage on acid Tatum subsoil. If confirmed under field conditions, such a difference could be economically significant in reclaiming acidic marginal land and in producing forage at low cost.

Differential Al tolerance in the two genotypes was confirmed in nutrient solutions. For example, with 8 mg Al L^‐1 added, both top and root dry weights of 860 were significantly higher than those of 822, but with no Al added, these growth differences disappeared.

Mineral analyses of plants did not shed much light on mechanisms of differential acid soil or Al tolerance. For example, Al concentrations in plant tops associated with toxicity varied from 33–43 ug g^‐1 in nutrient solutions containing Al to 119–283 ug g^‐1 in acid soil It appears that elucidation of Al‐adaptive mechanisms will require physiological and biochemical studies at the cellular level.     

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.     

Tolerance of seven tropical pasture grasses to excess manganese

Abstract

Setaria and paspalum were found to be very tolerant of excess Mn. Green panic and sorghum were somewhat less tolerant with foliar symptoms due to excess Mn being exhibited in plants containing 1000 ppm Mn and yield reductions occurring in plants containing Mn concentrations of the order of 2000 ppm. Excess Mn did not effect the early seedling growth of sabi grass but regrowth was severely depressed. Rhodes grass and buffel grass were severely effected by excess manganese. Regrowth of these two species was more adversely effected than initial seedling growth indicating that these species probably would not survive to maintain a stable pasture in Mn toxic situations.

Accumulation of excess Mn was accompanied by a linear decline in Ca concentrations in all species.     

Manganese toxicity in bush bean as affected by concentration of manganese and iron in the nutrient solution

An experiment was conducted to clarify the relationship between Mn toxicity and Fe deficiency in bush snap bean (Phaseolus vulgaris L. cv. ‘Wonder Crop No. 2'). Seedlings were grown in full strength Hoagland No. 2 solution at pH 6.0 for ten days. Six concentrations of Mn as MnCl₂.4H₂O were used in combination with three concentrations of Fe as FeEDTA.

Toxicity symptoms, induced by low levels of Mn (0.1 ppm and above), included: small brown necrotic spots and veinal necrosis on primary leaves; necrosis on primary leaf petioles; interveinal chlorosis, with or without brown necrotic spots, on trifoliate leaves; and brown necrotic spots on stipules. Manganese toxicity symptoms were alleviated or prevented by increasing Fe concentration in the nutrient solution.

Manganese concentration in the leaves increased with increasing Mn and decreased with increasing Fe concentration in the nutrient solution, Iron concentration in the roots increased with increasing Fe concentration in the nutrient solution; however, Fe concentration in the leaves was not significantly affected by increasing Mn concentration in the solution culture. Manganese toxicity symptoms developed when Mn concentration in the leaves reached about 120 ppm.

A decrease in the Fe/Mn ratio in the nutrient solution resulted in a proportionate decrease in that of the leaves. Manganese toxicity symptoms occurred when the Fe/Mn ratio in the solution was 10.0 and below, or when the ratio in the leaves was less than 1.5. The ratio of Fe/Mn in the solution required for optimum growth of ‘Wonder Crop No. 2’ bean, without Mn toxicity symptoms, was in the range of 20.0 to 25.0.

Results indicate that the chlorosis on bush bean leaves induced by excessive Mn in the nutrient solution was due to excessive accumulation of Mn and not to Fe deficiency.     

DRY MATTER PRODUCTION AND LEAF ELEMENTAL CONCENTRATIONS OF RAMBUTAN GROWN ON AN ACID ULTISOL

Little is known about the adaptability of rambutan (Nephelium lappaceum) to highly acidic soils rich in aluminum (Al). A 2-yr field study was conducted to determine the effects of various levels of soil Al on dry matter production, plant growth, and nutrient concentration in the leaves of four cultivars of rambutan. Cultivars and the cultivar x year interaction were not statistically significant for most variables measured in the study. Total, leaf, petiole, stem and root dry weights significantly increased at soil Al concentrations ranging from 0.67 cmol kg^?1 to 11.0 cmol kg^?1. At this range of soil Al, the concentrations of Al and manganese (Mn) in leaf tissue declined sharply. The results of this study demonstrate that rambutan is highly tolerant to acid soils and that tolerance may involve an Al- and Mn- exclusion mechanism.     

Acid soil tolerances of wheat lines selected for high grain protein content

Literature suggests that nitrogen (N) metabolism is involved in differential acid soil (Al) tolerances among wheat (Triticwn aestivum L. en Thell) genotypes. Atlas 66 wheat is characterized by acid soil and aluminum (Al) tolerance, nitrate (NO₃ ^‐) preference, pH increase of the rhizosphere, high nitrate reductase activity, and high protein in the grain. Atlas 66 has been used as a high protein gene donor in the development of new high protein wheat lines at Lincoln, NE. The objective of our study was to determine the acid soil tolerances of such lines and to relate such tolerances to their abilities to accumulate grain protein when grown on near‐neutral, non‐toxic soils. Twenty‐five experimental lines, nine cultivars not previously classified as Al‐tolerant or ‐sensitive and three cultivars previously classified according to acid soil tolerance, were grown for 28 days in greenhouse pots of acid, Al‐toxic Tatum subsoil. Relative shoot dry weight (pH 4.35/pH 5.41%) varied from 83.2% for Atlas 66 to 19.3% for Siouxland. Atlas 66 was significantly more tolerant to the acid soil than all other entries except Edwall. Yecorro Roja and Cardinal were intermediate in tolerance. None of the high protein lines approached Atlas 66 in tolerance, but two lines (N87U106 and N87U123) were comparable to Cardinal (relative shoot yield = 54%) which is used on acid soils in Ohio. At pH 4.35, the most acid soil tolerant entries contained significantly lower Al and significantly higher potassium (K) concentrations in their shoots than did sensitive entries. Shoots of acid soil sensitive entries, Scout 66, Siouxland, Plainsman V, and Anza contained deficient or near deficient concentrations of K when grown at pH 4.35. Acid soil tolerance was not closely related to calcium (Ca), magnesium (Mg), phosphorus (P), manganese (Mn), or iron (Fe) concentrations at pH 4.35. Liming the soil to pH 5.41 tended to equalize Al and K concentrations in shoots of tolerant and sensitive entries. Results indicated that acid soil tolerance and grain protein concentrations were not strongly linked in the wheat populations studied. Hence, the probability of increasing acid soil tolerance by crossing Atlas 66 with Nebraskan wheat germplasm is low. However, the moderate level of acid soil tolerance in N87U106 and N87U123 (comparable to that of Cardinal) may be useful in further studies.     

Differential tolerance of bush bean cultivars to excess manganese in solution and sand culture

Nineteen bush bean cultivars were screened for tolerance to excess Mn in nutrient solution and sand culture experiments. Seven‐day‐old seedlings were treated with full strength Hoagland No. 2 nutrient solution containing different Mn concentrations for 12 days in the greenhouse.

Cultivars showing the greatest sensitivity to Mn toxicity were ‘Wonder Crop 1’ and ‘Wonder Crop 2'; those showing the greatest tolerance were ‘Green Lord’, ‘Red Kidney’ and ‘Edogawa Black Seeded’.

Leaf Mn concentration of plants grown in sand culture was higher than that for plants grown in solution culture. The lowest leaf Mn concentration at which Mn toxicity symptoms developed, was higher in tolerant than in sensitive cultivars. The Fe/Mn ratio in the leaves at which Mn toxicity symptoms developed, was higher in the sensitive cultivars than in the tolerant ones.

We concluded that Mn tolerance in certain bush bean cultivars is due to a greater ability to tolerate a high level of Mn accumulation in the leaves.     

Excess trace metal effects on cotton: 2. Copper,zinc, cobalt and manganese in Yolo loam soil

Abstract

Two cultivars of cotton (Gossypium spp.) were grown in Yolo loam soil (soil pH about 6) in pots in a glasshouse to determine phytotoxic effects of excesses of Cu, Zn, Co, and Mn. Leaf yields of cv. Acala SJ‐2 were depressed 35% by 400 μg Cu/g soil, 54% by 400 μg Zn/g soil, 98% by 400 μg Co/g soil, and 84% by 2000 μg Mn/g soil. Leaf metal concentrations at these application levels in μg/g leaf were 12.0 Cu, 520 Zn, 243 Co, and 14780 Ma, respectively. Plants were tolerant of in / dry leaves of 10 Cu, 157 Zn and 444 Mn. The concentration for Co could not be ascertained. Leaf yields of cv. Giza 70 were depressed 53% by 400 μg Cu/g soil, 25% by 400 μg Zn/g soil, 92% by 400 μg Co/g soil and 90% by 2000 μg Mn/g soil. This cv. was more tolerant of Zn than Acala SJ‐2. Leaf metal concentrations at these application levels in μg/g leaf were 11.8 Cu, 312 Zn, 224 Co, and 18300 Mn respectively. Gradients of these four elements existed from leaves to stems. Many interactions with other elements were observed.     

Differential tolerances of oat cultivars to aluminum in nutrient solutions and in acid soils of Poland

Aluminum tolerant oat cultivars are needed for use on acid soil sites where neutralization of soil acidity by liming is not economically feasible. Oat germplasm in Poland has not been examined for range of Al tolerance. Eleven Polish oat cultivars were screened for Al tolerance in nutrient solutions containing 0, 5 and 15 mg L^‐1 Al. Three of these cultivars showing high to moderate tolerance to Al in nutrient solutions were also grown in greenhouse pots of soil and in field plots of soil over a pH range of 3.8 to 5.5 as determined in 1 N KC1.

The eleven oat cultivars differed significantly in tolerance to Al in nutrient solutions. Based on relative root yield (15 mg L^‐1 Al/no A1%), the cultivars ‘Solidor’ and ‘Diadem’ were most tolerant and ‘Pegaz’ and ‘B‐20’ were least tolerant. For these three cultivars, the order of tolerance to acid soil agreed with the order of tolerance to Al in nutrient solution ‐ namely, Solidor > Diadem > Leanda. Hence, for these cultivars, the nutrient solution methods used appear adequate for selecting plants that are more tolerant to Al in strongly acid soils. Additional study is needed to assess the value of this method for screening a broad range of germplasm.

Superior tolerance of the Solidor cultivar to acid soil was associated with significantly higher concentrations of N in the grain. Hence, results suggest that selecting for acid soil or Al tolerance may increase N efficiency in oats.     

Effects of excess soil manganese on stomatal function in two soybean cultivars

Manganese tolerant ‘Lee’ and Mn sensitive ‘Forrest’ soybean cultivars were grown in a potting soil with no known Mn toxicity and in Loring soil treated with excess Mn. Manganese toxicity in Loring soil was induced by the addition of Mn at 0, 100, 200 and 400 ug g^‐1 as MnSO₄.H₂O. A preliminary experiment was conducted to determine the appropriate Mn stress levels for Lee and Forrest soybean cultivars in Loring soil. Because the Loring soil produced severe Mn toxicity in both cultivars, even with an intial pH of 4.9 and no added Mn, CaCO₃ (2 g kg^‐1 ) was added to Increase the pH to 6–6.3. Soil was analysed for extractable and water soluble Mn and plants for Mn, Ca and Fe.

A second experiment was conducted to determine the effect of Mn toxicity on stomatal function. The procedure was the same as in the first experiment except that the CaCO₃ treatment was 2.5 g kg^‐1 to raise soil pH to 6.2 ‐6.5. Plants were grown in a greenhouse for 10 days and then moved to a growth chamber before making stomatal conductance measurements. A steady state porometer (LI 1600) was used. Results indicated that Mn toxicity closed stomates and decreased transpiration rates. This effect was more pronounced in Mn sensitive Forrest than in Mn tolerant Lee.     

Evaluation of switchgrass entries for acid soil tolerance

Abstract

Crop and forage yields are significantly reduced by strong soil acidity throughout much of the northeastern United States. Switchgrass (Panicum virgatum L.) is a valuable perennial warm‐season pasture species generally regarded as tolerant to stress conditions, i.e., infertile, dry, or low pH soils; however, switchgrass has not been studied for variability in acid soil tolerance. The objectives of this study were (a) to compare the responses of different switchgrass entries to soil acidity, and (b) to identify selected agribotanical trait response to unlimed (‐L) and limed (+L) soil. Sixteen entries (cultivars, germplasms, and breeding populations) were studied in short‐ and meso‐term experiments. Unlimed (pH 4.9) and limed (pH 5.9) treatments of a sandy loam soil (Typic Dystrochrept) were used in both experiments. Switchgrass seedlings were exceptionally tolerant of soil acidity in the short‐term experiment. In the meso‐term experiment, acid soil stress significantly reduced all agribotanical traits (plant height, leaf area, top weight, and root weight) determined in the study when compared to +L plants. There were significant, positive correlations among the agribotanical traits; however, the effect of ‐L soil was more obvious on root weight and less so on plant height. Entries 922 GST6, 920 AST6, 921 DST6, and 922 BST6 showed superior general adaptability and promising forage production, while cultivars Carthage and PI 142138 were acid soil tolerant with low productivity. Our data suggests that selection for increased acid soil tolerance in switchgrass may be possible and would result in improved productivity of this grass in acid soil environments.     

Salt Tolerance and K/Na Ratio of Some Introduced Forage Grass Species Under Salinity Stress in Irrigated Areas

Salinity is a limiting factor for forage productivity in irrigated areas. The aim of this study was to evaluate the salt tolerance index (STI), the K/Na ratio, and the forage quality of several introduced cool season grass species in irrigated agriculture. Four irrigated water salinity concentrations were used (control, 4000, 8000, and 12000 ppm sodium chloride (NaCl)), and four grass cultivars belonging to three species were established under greenhouse conditions at the Qassim University Agricultural Research and Experimental Station during the 2012 and 2013 growing seasons (perennial ryegrass (Lolium perenne L., cvs. Aries and Quartet), endophyte-free tall fescue (Festuca arundinacea Schreb., cv. Fawn), and orchardgrass (Dactylis glomerata L., cv. Tekapo)). A randomized complete block design (RCBD) using three replications was used. Cultivars were evaluated based on their dry weights (g m^?2) and forage quality. Additionally, the STI and potassium (K⁺) and sodium (Na⁺) concentrations in the studied grass cultivars were evaluated. The dry weights of the grasses decreased significantly as the salinity level of the irrigation water increased. At a salinity of 4000 ppm, the Aries perennial ryegrass had the highest dry weight at both sample cuttings. The Aries, Fawn, and Quartet grasses had the highest STI values. The percent of K⁺ and the K/Na ratio increased as the salinity of the irrigation water increased for the Fawn tall fescue and Quartet perennial ryegrass. In the previously cultivars, the percentage of Na⁺ decreased as the salinity level of the irrigation water increased, which was in contrast with the results observed for the Tekapo orchardgrass.     

Effect of cultivar and cadmium rate upon the nutrient content of soybean plants

An experiment was conducted to evaluate the effect of soybean (Glycine max L.) cultivar, Cd rate, and cultivar x Cd rate interaction upon nutrient concentrations in the plant. Cultivars rated as T (tolerant) or S (susceptible) to Cd were included in the study. A factorial combination of 10 cultivars and 4 levels of Cd were randomized in 4 replications of a completely randomized design. Additions of CdCl₂ dissolved in distilled water were made to weighed quantities of dry soil. The soil was a Flanagan silt loam (Aquic Argiudoll). Four weeks after planting, plants were harvested, air dried and dry ashed. Chemical determinations of Zn, Fe, Mn, Cu, K, Ca, Mg and P in plants were made by emission spectroscopy.

Nutrient concentrations were affected by cultivar and rate of Cd and generally, nutrient concentrations decreased as rate of Cd increased. The Cd linear x cultivar interaction significantly affected plant concentration of each element except P indicating that the linear effect of Cd was not consistent among all cultivars. A comparison of “susceptible”; cultivars with “tolerant”; cultivars showed significant differences in nutrient concentration of each element except K. Plant K concentration was significantly associated with a Cd linear x T (tolerant) vs. S (susceptible) interaction indicating that the linear trend due to Cd rate differed between cultivars rated S or T to Cd.     

NUTRIENT UPTAKE AND USE EFFICIENCY BY TROPICAL LEGUME COVER CROPS AT VARYING PH OF AN OXISOL

Oxisols comprise large soil group in tropical America. These soils are acidic and have low fertility. Use of tropical legume cover crops in cropping systems is an important strategy to improve fertility of these soils for sustainable crop production. Data are limited on nutrient uptake and use efficiency of tropical cover crops under different acidity levels. The objective of our study was to evaluate growth and nutrient uptake parameters of sixteen tropical legume cover crops under three soil pH (5.1, 6.5, and 7.0) of an Oxisol. Shoot dry weight was influenced significantly by pH and cover crop treatments and their interactions, indicating that cover crops used had differential responses to changing soil pH levels. Overall, shoot dry weight decreased when soil pH was raised from 5.1 to 7.0, indicating acidity tolerance of cover crops. Nutrient concentration (content per unit of dry weight), uptake (concentration X dry weight), and nutrient use efficiency (dry weight of shoot per unit of nutrient uptake) varied significantly among cover crops. The variation in nutrient uptake and use efficiency among cover crop species was associated with variation in shoot dry matter production. Significant variation among crop species in dry matter production and low C/N ratios (average value of 14.25) suggest that cover crops which produced higher dry matter yield like white jack bean, gray mucuna bean, black mucuna bean, mucuna bean ana, and lablab are important choices for planting in tropical soils to recover large amount of macro and micronutrients, and to prevent such nutrient leaching in soil plant systems.