SOIL NITROGEN

Soils from experiments receiving various treatments in the field were used to investigate the effects of different amounts and forms of organic matter in a clay and a sandy soil on the inter-correlations between several laboratory methods of measuring available-N. The correlations between some of these measurements, and the growth and N uptake of ryegrass grown in the glasshouse with and without added fertilizer-N were also investigated. Seven clay soils and eight sandy soils were used, containing different amounts of organic matter of different kinds, as a result of various field treatments. For the sandy soils, one sample was taken from each plot of the experiment which allowed the effects of field variations on the values determined in the laboratory to be measured. The correlations between methods of measuring available-N showed that measurements obtained by aerobic incubation, anaerobic incubation, and nitrogen extracted by boiling water, correlated best with one another. These measurements also correlated best with the performance of ryegrass in the glasshouse. N uptake by ryegrass from soils without fertilizer-N always correlated better with measurements of available-N than did dry matter produced. With added fertilizer-N, dry matter correlated better with available-N than did N uptake at the first cut but worse for the total of three cuts. Fertilizer-N recovered in the grass at the first cut was significantly and negatively correlated with available-N. Values of available-N from the individual samples of the sandy soil showed that those for aerobic incubation had the largest standard error and had the greatest range expressed as a per cent of the mean value, and those for nitrogen extracted by boiling water least error and range. All methods correlated similarly with the performance of ryegrass in the glasshouse. All three methods successfully identified the treatments giving most available-N.     

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.     

Derivation of a Dynamic Model of the Kinetics of Nitrogen Uptake Throughout the Growth of Lettuce: Calibration and Validation

A kinetic model of nitrogen (N) uptake throughout growth was developed for lettuce cultivated in nutrient solution under varying natural light conditions. The model couples nitrogen uptake with dry matter accumulation using a two-compartment mechanistic approach, incorporating structural and non-structural pools. Maximum nitrogen uptake rates are assumed to decline with shoot dry weight, to allow for the effects of plant age. The model was parameterized using data from the literature, and calibrated for differences in light intensity using an optimization algorithm utilizing data from three experiments in different growing seasons. The calibrated model was validated against the data from two independent experiments conducted under different light conditions. Results showed that the model made good predictions of nitrogen uptake by plants from seedlings to maturity under fluctuating light levels in a glasshouse. Plants grown at a higher light intensity showed larger maximum nitrogen uptake rates, but the effect of light intensity declined towards plant maturity.     

A small increase in the concentration of phosphorus in the sown seed increased the early growth of wheat

Wheat seed from the same origin but with different concentrations of phosphorus (P) (1.3 and 1.7 g P/kg) was grown on P responsive soils in a glasshouse and a field experiment in Western Australia. The effects of the concen‐ tration of P in the seed (seed P) on the growth of shoots and roots during tillering and booting (glasshouse) or ear emergence (field), and on the grain yields of the wheat plants, were measured. The concentrations of P in these plant tissues were also measured. In both the glasshouse and the field, the dry weights of whole shoots (WS) during tillering increased with seed P, irrespective of soil P. The dry weights of WS measured at later stages of growth and the grain yields, however, were unaffected by seed P. The concentrations of P measured in the WS and grain were also unaffected by seed P.     

Boron in vegetation in relationship to a coal‐burning power plant

Abstract

Plants grown in water from an ash‐settling pond at a coal‐burning power generating plant near Moapa, Nevada, those grown in a glasshouse in soil to which ash collected from the plant had been added, and native plants growing around the ash ponds at the plant site all had elevated B concentrations.     

SOURCES OF SULFUR FOR DRY MATTER,SEED YIELD,AND OIL CONCENTRATION OF CANOLA GROWN IN SULFUR DEFICIENT SOILS OF SOUTH-WESTERN AUSTRALIA

Leaching of sulfur (S) on sandy soils may limit the effectiveness of S fertilizers especially when applied at sowing. The effectiveness of S sources for canola (oil seed rape, Brassica napus L.) grown in sandy low S soils of south-western Australia is not known. This study was completed to determine the relative effectiveness of gypsum and a gypsum-based by-product from synthetic rutile processing called Canola Blue for canola grown in low S soils of the region. Canola Blue is a mixture of gypsum and elemental S, and is granulated so its effectiveness may vary from gypsum. We measured the effectiveness of the two S sources in the glasshouse for young seedling growth and for minimizing S leaching. In the four field experiments, the two S sources were evaluated for relative effects on canola seed yield and the concentration of oil in seed. Canola Blue applied at sowing was as effective as gypsum for canola growth in the glasshouse and when applied at 35 days after sowing (DAS) was as effective as gypsum for seed yield in the field. For the glasshouse study, Canola Blue when applied to the soil surface (topdressed) at 35 DAS was as effective as gypsum in achieving a rapid recovery of leaves from S deficiency symptoms and of shoot growth. Where S deficiency appears during the growing season, topdressing with Canola Blue appears to be as effective under the conditions of this experiment as was gypsum. However, the S in Canola Blue was less prone to leaching than that applied as gypsum.     

How reliable are results of pot experiments?

Abstract

Results of pot experiments depend much on the environmental conditions under which they are conducted and on “personal factors”; such as the choice of the type of pots, rates of fertilisers applied, the way these fertilisers are applied, growing conditions in the glasshouse, and the decision when to terminate the experiment. The majority of pot experiments are conducted under environmental conditions which seldom or never occur in the field. We therefore cannot extrapolate their results to the field unless the experiments deal with growing factors which dominate all others.     

Different Methods of Mechanical Stress in Controlling the Growth of Lettuce and Cauliflower Seedlings

Abstract

Cauliflower and lettuce seedlings were treated with different methods of mechanical stress (MS): brushing (1.5 min/day) with bond typing paper or with burlap, unidirectional fanning (5 min/day), or shaking the seedlings on platforms (5 min/day). In experiment 1 the plants were treated once a day. In experiment 2 the treatments were divided into two periods. The responses of both species to brushing were clearly stronger than to fanning or to shaking. Brushing reduced plant height and the first leaf length and width in both species. The fresh weight and dry matter content in cauliflower shoots were also affected. There were differences in reactions between experiments 1 and 2, caused by various environmental conditions in the glasshouse and the frequency of applied MS.     

Q/I relations and electroultrafiltration of soils as measures of potassium availability to plants

The equilibrium activity ratio (AR_o) of soil potassium and the K extracted by electroultrafiltration (EUF) within a desorption time of 10 min (EUF₁₀) were compared as measures of K availability indicated by K uptake and dry matter yield of barley plants grown in four soils receiving different rates of K fertilization in a glasshouse experiment. As could be expected, both methods indicated that K intensity in soils increased with higher amounts of K dressings and decreased with progressive crop growth. With EUF₁₀, 56–77% of the variation in plant response in dry matter yield and K uptake could be explained, where as with AR_o, it was only 36–65%. There was good linear correlation between AR_o, and EUF₁₀ for a particular soil; but there was differential variation in the two parameters for the different soils. When compared on the basis of plant response, EUF₁₀ was found to better describe K availability to plants and differentiate better between soils of different K selectivity.     

Relative Phosphorus Phytoavailability of Different Phosphorus Sources

Understanding differences in the phytoavailability of various phosphorus (P) sources should improve matching P additions to plant needs and minimize excessive buildup of bioavailable P, which can degrade aquatic systems. We evaluated relative P phytoavailability (RPP) of different P sources in glasshouse and field studies. Bahiagrass (Paspalum notatum Fluggae), ryegrass (Lolium perenne L.), and a second bahiagrass crop were grown in succession in a P‐deficient soil amended with four sources of P (triple superphosphate (TSP), Boca Raton and Pompano; biosolids, and poultry manure), each applied at two rates in the glasshouse study and to an established bahiagrass pasture in the field. The RPP values estimated from plant P uptake of each organic source of P relative to TSP in the glasshouse were similar for the three croppings and similar to the estimates derived from the field study, but varied for the different P sources. Values ranged from 30% for poultry manure to 85% for Boca Raton biosolids. Boca Raton biosolid P was as readily available as P in TSP and would be classified as a high RPP (>75% RPP) source, but Pompano biosolids and manure would be classified as moderate RPP materials (25–75% RPP). The RPP values observed in manure and Pompano biosolid treatments are consistent with 50% “effectiveness” suggested for biosolid P in U.S. Environmental Protection Agency (USEPA) guidelines, whereas P bioavailability of Boca Raton biosolids is similar to mineral fertilizer.     

Absorption of various types of chelated copper in a low concentration range by cucumber

Two experiments were conducted to compare absorption of copper (Cu) from cupric chloride (CuCl₂) and various types of chelated Cu in a low concentration range by cucumbers. In the first experiment, two varieties of cucumber were grown on rockwool for 40 days in a glasshouse with standard nutrient solution which contained six different concentrations of CuCl₂ (0, 0.05, 0.10, 0.20, 0.40, and 0.80 μmol/L). Copper deficiency symptoms were examined during the growing period, and the total nitrogen (N), iron (Fe), manganese (Mn), zinc (Zn), and copper contents of young fully grown leaves were measured. There were no differences among treatments in the leaf contents of N and Mn. Copper contents increased and Zn decreased with increasing Cu levels. The content of Cu at the three low Cu treatments (including no Cu addition) were in the deficient range (48–65 μmol/kg dry matter). The zero Cu level had paler green leaves than other treatments. No differences were apparent between varieties. The second experiment was carried out under exactly the same conditions as the first, but on the basis of the results of the first experiment, Cu treatments were 0, Cu‐EDDHA at 0.4, Cu‐DTPA at 0.4, Cu‐EDTA at 0.4, Cu‐NTA at 0.4, CuCl₂ at 0.4 μmo/L as Cu²⁺. After the experiment, the total N, Fe, Mn, Zn, and Cu contents of young, fully grown leaves were measured. There were no differences between treatments in the leaf contents of Cu except zero Cu level. They were in the range of 101–119 μmol/kg dry matter. At no Cu addition treatment, the Cu content was only 31 μmol/kg dry matter which is considered to be the deficiency level. For the other examined elements, there were no differences among the treatments and varieties. From these data it was concluded that the availability of these chelated Cu types were the same as CuCl₂ under the conditions of the experiments conducted.     

Metabolite profiling of maize kernels--genetic modification versus environmental influence

A metabolite profiling approach based on gas chromatography-mass spectrometry (GC-MS) was applied to investigate the metabolite profiles of genetically modified (GM) Bt-maize (DKC78-15B, TXP 138F) and Roundup Ready-maize (DKC78-35R). For the comparative investigation of the impact of genetic modification versus environmental influence on the metabolite profiles, GM maize was grown together with the non-GM near-isogenic comparators under different environmental conditions, including several growing locations and seasons in Germany and South Africa. Analyses of variance (ANOVA) revealed significant differences between GM and non-GM maize grown in Germany and South Africa. For the factor genotype, 4 and 3%, respectively, of the total number of peaks detected by GC-MS showed statistically significant differences (p < 0.01) in peak heights as compared to the respective isogenic lines. However, ANOVA for the factor environment (growing location, season) revealed higher numbers of significant differences (p < 0.01) between the GM and the non-GM maize grown in Germany (42%) and South Africa (10%), respectively. This indicates that the majority of differences observed are related to natural variability rather than to the genetic modifications. In addition, multivariate data assessment by means of principal component analysis revealed that environmental factors, that is, growing locations and seasons, were dominant parameters driving the variability of the maize metabolite profiles.     

Changes in root length at the reproductive stage of maize plants grown in the field and quartz sand

The aims of this work were to investigate possible reasons for root mortality of maize plants at the reproductive stage and relationships between root mortality and internal sugar and external nitrogen (N) supply. Maize (Zea mays L.) plants were grown in the field in fertile soil and in a greenhouse in quartz sand with sufficient or deficient N supply. Deficient N supply reduced plant growth and total N uptake by 38% and 52%, respectively. The lengths of the seminal roots and of the early initiated adventitious roots of the first two whorls declined after reaching their maximum values before silking, no matter whether the plants were grown in the field or in quartz sand in the greenhouse. The lengths of the adventitious roots from higher nodes of plants grown in quartz sand, irrespective of N supply, did not decrease at the reproductive stage despite of decreasing sugar concentrations. In contrast, under field conditions, the length of adventitious roots from higher nodes decreased during grain filling. Total activity of all roots of greenhouse‐grown plants as deduced from translocation of N and cytokinins in the xylem exudate reached peak values at the end of the growing period, whereas in field‐grown plants N translocation decreased and cytokinin translocation did not change toward the end of the growing period. The results indicate that the pattern of root growth and mortality of maize plants in the reproductive stage was not affected by external N supply. Differences between glasshouse‐ and field‐grown plants are possibly due to effects of soil biota, which have to be further studied.     

Promotion of plant growth by an auxin-producing isolate of the yeast Williopsis saturnus endophytic in maize (Zea mays L.) roots

A plant-growth-promoting isolate of the yeast Williopsis saturnus endophytic in maize roots was found to be capable of producing indole-3-acetic acid (IAA) and indole-3-pyruvic acid (IPYA) in vitro in a chemically defined medium. It was selected from among 24 endophytic yeasts isolated from surface-disinfested maize roots and evaluated for their potential to produce IAA and to promote maize growth under gnotobiotic and glasshouse conditions. The addition of l-tryptophan (L-TRP), as a precursor for auxins, to the medium inoculated with W. saturnus enhanced the production of IAA and IPYA severalfold compared to an L-TRP-non-amended medium. The introduction of W. saturnus to maize seedlings by the pruned-root dip method significantly (P<0.05) enhanced the growth of maize plants grown under gnotobiotic and glasshouse conditions in a soil amended with or without L-TRP. This was evident from the increases in the dry weights and lengths of roots and shoots and also in the significant (P<0.05) increases in the levels of in planta IAA and IPYA compared with control plants grown in L-TRP-amended or non-amended soil. The plant growth promotion by W. saturnus was most pronounced in the presence of L-TRP as soil amendment compared to seedlings inoculated with W. saturnus and grown in soil not amended with L-TRP. In the glasshouse test, W. saturnus was recovered from inside the root at all samplings, up to 8 weeks after inoculation, indicating that the roots of healthy maize may be a habitat for the endophytic yeast. An endophytic isolate of Rhodotorula glutinis that was incapable of producing detectable levels of IAA or IPYA in vitro failed to increase the endogenous levels of IAA and IPYA and failed to promote plant growth compared to W. saturnus, although colonization of maize root tissues by R. glutinis was similar to that of W. saturnus. Both endophytic yeasts, W. saturnus and R. glutinis, were incapable of producing in vitro detectable levels of gibberellic acid, isopentenyl adenine, isopentenyl adenoside or zeatin in their culture filtrates. This study is the first published report to demonstrate the potential of an endophytic yeast to promote plant growth. This is also the first report of the production of auxins by yeasts endophytic in plant roots.     

Adaptation of ecotypes and cultivars of subterranean clover (<Emphasis Type="Italic">Trifolium subterraneum</Emphasis> L.) to German environmental conditions and its suitability as living mulch

Abstract A total of 320 accessions of subterranean clover (Trifolium subterranenum L.) were screened for adaptation to the environmental conditions in southern Germany, as well as their suitability as cover crops or living mulches. The accessions, derived from collections of the Department of Agriculture and Food Western Australia and the International Research Center for Agriculture in Dry Areas, were propagated in the greenhouse and grown in rows. Selected accessions were then tested in plots and as an intercrop in wheat, in order to test their suitability as living mulch. Moreover, a frost resistance screening was carried out in a climate chamber. Adaptation to southern German conditions and frost tolerance was generally better than expected, as most accessions survived winters with snow cover and transitory temperatures as low as \(-\,10\,^\circ \)C. Accessions with particularly high frost tolerance were identified and several accessions persisted over four generations of self-reseeding. Although there was a large range of morphological characteristics, no differences concerning their suitability as living mulch could be observed. The results suggest that subterranean clover is sufficiently winter hardy to be grown as an overwintering cover crop or living mulch in southern Germany. Commercially available cultivars appear suitable in the first instance, even though these have not been selected for cold winters. However, adaptation might be further improved by targeted selection among accessions.     

5-(2,6-difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)- 1,2-isoxazoline as a useful rice herbicide

5-(2,6-difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)-1,2-isoxazoline derivative was synthesized, and its herbicidal activity was assessed under glasshouse and flooded paddy conditions. 5-(2,6-Difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)-1,2-isoxazoline demonstrated good rice selectivity and potent herbicidal activity against annual weeds at 125 g of a.i. ha(-1) under greenhouse conditions. Soil application of this compound showed complete control of barnyard-grass to the fourth leaf stage at 250 g of a.i. ha(-1). Field trials indicated that this compound controlled annual weeds rapidly with a good tolerance on transplanted rice seedlings by post-emergence and soil application. This compound showed a low mammalian and environmental toxicity in various toxicological tests.     

Nitrogen nutrition of asparagus seedlings

Asparagus seedlings (cv. Limbras 10) were grown in a glasshouse for 20 weeks with five levels of nitrogen liquid feed. Growth was greatly retarded at low N rates. Best growth occurred with weekly feeds of 200–300 mg N/litre. Total nitrogen concentrations of these plants were 3.5–4.5% N (dry weight). Nitrate nitrogen concentrations were 600–1500 yg N/g.     

Effect of sulfur and molybdenum levels on growth,nitrate‐assimilation,and nutrient con‐tent of Phalaris

An experiment was conducted with Phalaris aquatica L. cv. Sirolan under hydroponic conditions in the glasshouse at constant temperature of 25°C and natural sunlight. Plants were grown in double pot system with four sulfur and three molybdenum levels along with all the major‐ and micro‐nutrient elements. There was increase in growth, nitrate‐reductase activity and contents of most of the nutrient elements at all levels of sulfur and 1.68 μ/L molybdenum. Molybdenum at 3.36 μg/L level inhibited growth and nitrate‐reductase activity and decreased concentration of nutrient elements in plant. The inhibitory effect of higher level of molybdenum is perhaps mediated through its role in the nitrate‐reductase.     

Virgin olive oil volatile compounds from lipoxygenase pathway and characterization of some italian cultivars.

Fruits from seven different varieties of Olea europaea L., grown in the same environmental conditions, were harvested in two succeeding years at the same ripening degree and immediately processed. The oils obtained were submitted to gas chromatographic determination of the volatile compounds extracted by dynamic headspace technique. The results demonstrated that the accumulation of the different metabolites in the oils obtained from the various cultivars were strictly connected with the varietal parameter because of the enzyme differences genetically determined. This feature made possible the differentiation of the examined cultivars on the basis of the percent of each metabolite from the enzymatic transformation of 13-hydroperoxides of linolenic acid. Oils from Picual and Koroneiki varieties cultivated in Spain and Greece, respectively, showed contents of volatiles very similar to those detected in the oils of the same varieties cultivated in Italy, proving that they were not significantly influenced by the environmental conditions.