Showing papers in "Journal of Plant Nutrition and Soil Science in 2013"

Methods of collection of plant root exudates in relation to plant metabolism and purpose: A review

Abstract: The aim of this work is to review the current knowledge on the effects of plant metabolism (C3, C4, and CAM) on root exudation and on the methods of exudate collection as well as the use of such exudates for analyses, testing of microbial response, degradation of pollutants, enzymatic activities, and occurrence of allelochemicals. We examine the advantages and disadvantages of each method as related to the downstream use of the exudates. The use of continuous percolation of solid cultivation medium with adjustment of nutrient-solution strength appears to be a promising methodology for the determination of root exudation rates and qualitative composition of exuded compounds. The method mimics rhizosphere conditions, minimizing the artificial accumulation of compounds, alteration of plasma-membrane permeability, ATPase activity, and the impacts of inhibitors or stimulators of root enzymes. Of particular significance is the fact that the adjustment of strength of nutrient solution and percolation enables universal and also long-term use of the method, allowing high exudation yield by minimizing influx and maximizing efflux rates of exuded compounds at high nutrient-solution strength. Furthermore, it facilitates assessment of the effect on soil microbial populations and their ability to degrade pollutants. Enzymatic activities can be assessed when a low strength of nutrient solution is used, with percolation of the exudates directly into tested soils. Composition of root exudates, regulation of root enzymes, and plant response to nutrient deficiency can be assessed by measuring net efflux or influx rates. The impact of heavy metals and other type of mechanical, chemical, and biological stresses differs according to the type of plant metabolism. This has significant consequences on transformations in plant communities, both structurally and functionally, and impacts upon crop nutrition, with respect to global climate change, and the use of plants for phytoremediation purposes. Understanding the effects of different types of plant metabolism on root exudation with respect to genetic regulation of synthetic pathways through root enzymes and transport systems presents an important direction for future research.

Potassium–sodium interactions in soil and plant under saline-sodic conditions†

Abstract: About 7% of the total land around the globe is salt-affected causing a great loss to agriculture. Salt stress refers to the excessive amount of soluble salts in the root zone which induce osmotic stress and ion toxicity in the growing plant. Among toxic ions, sodium (Na+) has the most adverse effects on plant growth by its detrimental influence on plant metabolism in inhibiting enzyme activities. An optimal potassium (K+) : Na+ ratio is vital to activate enzymatic reactions in the cytoplasm necessary for maintenance of plant growth and yield development. Although most soils have adequate amounts of K+, in many soils available K+ has become insufficient because of large amounts of K+ removal by high-yielding crops. This problem is exacerbated under sodic or saline-sodic soil conditions as a consequence of K+-Na+ antagonism. Here K+ uptake by plants is severely affected by the presence of Na+ in the nutrient medium. Due to its similar physicochemical properties, Na+ competes with K+ in plant uptake specifically through high-affinity potassium transporters (HKTs) and nonselective cation channels (NSCCs). Membrane depolarization caused by Na+ makes it difficult for K+ to be taken up by K+ inward-rectifying channels (KIRs) and increases K+ leakage from the cell by activating potassium outward-rectifying channels (KORs). Minimizing Na+ uptake and preventing K+ losses from the cell may help to maintain a K+ : Na+ ratio optimum for plant metabolism in the cytoplasm under salt-stress conditions. It would seem a reasonable assumption therefore that an increase in the concentration of K+ in salt-affected soils may support enhanced K+ uptake and reduce Na+ influx via HKTs and NCCSs. Although very useful information is available regarding K+-Na+ homeostasis indicating their antagonistic effect in plants, current knowledge in applied research is still inadequate to recommend application of potassium fertilizers to alleviate Na+ stress in plants under sodic and saline-sodic conditions. Nevertheless some encouraging results regarding alleviation of Na+ stress by potassium fertilization provide the motivation for conducting further studies to improve our understanding and perspectives for potassium fertilization in sodic and saline-sodic environments.

Silicon decreases the arsenic level in rice grain by limiting arsenite transport

Abstract: Silicon (Si) reduces arsenic (As) levels in rice shoot and grain. However, the underlying mechanisms remain unclear. In this study, we examined the effect of Si application to three rice paddy soils on the dynamics of Si, iron (Fe), phosphorus (P), and As in the soil solution, As accumulation in rice straw, flag leaf, husk, brown rice, and polished rice, and on As speciation in polished rice. Silicon application to soil increased the concentrations of Si, Fe, As, and P in the soil solution, while the redox potential was unaffected. Arsenic concentrations of straw, flag leaf, and husk were reduced by half by Si application, while As concentrations of brown and polished rice were decreased by 22%. The main As species in polished rice was arsenite, As(III), with a fraction of 70%, followed by dimethylarsinic acid (DMA) and arsenate, As(V), with 24% and 6%, respectively. Silicon application to the soil did not affect DMA or As(V) concentration of polished rice, while the As(III) concentration was reduced by 33%. These results confirm that Si reduces As(III) uptake and translocation into the shoot. Furthermore, data indicate that decrease of As concentration of polished rice is due to decreased As(III) transport into grain. Possible underlying mechanisms are discussed.

Use of Rhizobium leguminosarum as a potential biofertilizer for Lactuca sativa and Daucus carota crops

Abstract: Microbial biofertilizers are becoming an effective tool for sustainable agriculture by means of the reduction of the use of chemical fertilizers. However, the knowledge of each specific plant–microorganism interaction is essential for a correct application. In this study, we analyzed the in vitro plant-growth-promotion mechanisms of a Rhizobium leguminosarum strain named PEPV16 isolated from Phaseolus vulgaris nodules. This strain was able to produce siderophores and indole acetic acid and to solubilize phosphate. Confocal microscopy showed that this strain was able to colonize the roots of two horticultural crops, Lactuca sativa L. (lettuce) and Daucus carota L. (carrot). Strain PEPV16 was also able to promote the plant growth of both plant species increasing the dry matter of shoots and roots of lettuce and carrots, respectively, as well as to increase the uptake of N and P in the edible parts of both plant species. These data confirmed the suitability of Rhizobium as biofertilizer for nonlegumes.

Potassium and stress alleviation: Physiological functions and management of cotton

Abstract: Potassium (K) plays a major role in the basic functions of plant growth and development. In addition, K is also involved in numerous physiological functions related to plant health and resistance to biotic and abiotic stress. However, K deficiency occurs widely resulting in poor growth, lost yield, and reduced fiber quality. This review describes the physiological functions of K and its role in stress relief and also provides some agronomic aspects of K requirements, diagnosis of soil and plant K status, and amelioration. The physiological processes described include enzymes and the regulation of organic-compound synthesis, water relations and stomates, photosynthesis, transport, cell signaling, and plant response to drought stress, cold stress, salt stress, as well as biotic stresses. The agronomic aspects of K fertilization include the K requirements of cotton, K uptake, and soil characteristics, genotypic variation in K uptake and use, and characteristics of K deficiency in cotton. In addition, diagnosis and amelioration of K soil and plant status is discussed.

Improving potassium acquisition and utilisation by crop plants

Abstract: To avoid loss of yield, crops must maintain tissue potassium (K) concentrations above 5–40 mg K (g DM)–1. The supply of K from the soil is often insufficient to meet this demand and, in many agricultural systems, K fertilisers are applied to crops. However, K fertilisers are expensive. There is interest, therefore, in reducing applications of K fertilisers either by improving agronomy or developing crop genotypes that use K fertilisers more efficiently. Agronomic K fertiliser use efficiency is determined by the ability of roots to acquire K from the soil, which is referred to as K uptake efficiency (KUpE), and the ability of a plant to utilise the K acquired to produce yield, which is referred to as K utilisation efficiency (KUtE). There is considerable genetic variation between and within crop species in both KUpE and KUtE, and chromosomal loci affecting these characteristics have been identified in Arabidopsis thaliana and several crop species. Plant traits that increase KUpE include (1) exudation of organic compounds that release more non-exchangeable soil K, (2) high root K uptake capacity, (3) early root vigour, high root-to-shoot ratios, and high root length densities, (4) proliferation of roots throughout the soil volume, and (5) high transpiration rates. Plant traits that increase KUtE include (1) effective K redistribution within the plant, (2) tolerance of low tissue K concentrations, and, at low tissue K concentrations, (3) maintenance of optimal K concentrations in metabolically active cellular compartments, (4) replacement of K in its non-specific roles, (5) redistribution of K from senescent to younger tissues, (6) maintenance of water relations, photosynthesis and canopy cover, and (7) a high harvest index. The development of crop genotypes with these traits will enable K fertiliser applications to be reduced.

The effects of potassium fertilization on water-use efficiency in crop plants†‡

Abstract: The supplies of water and nitrogen to a plant during its critical stages of growth are the main factors that define crop yield. A crop experiences irregular water deficits during its life cycle in rain-fed agriculture. An effective anti-stress-oriented approach therefore ought to focus on increasing the units of water productivity. The main objective of this conceptual review is to confirm that adequate K management can be used as an important tool to alleviate the negative effects of water deficit on plant growth, yield-component formation, and yield. The French and Schultz approach of using the water-limited yield (WLY) was modified in this review into a graphical form and was used to discriminate between yield fractions that depended on the volume of transpired water from those that were induced by K fertilizer. By using this method, it was possible to demonstrate the extent of several crop (winter wheat, spring triticale, maize, sugar beet) responses to the K supply. Yield increases resulting from K application mostly appeared under conditions of mild water deficit. As described for sugar beet, finding the critical period of crop K sensitivity is a decisive step in understanding its impact on water-use efficiency. It has been shown that an insufficient supply of K during crucial stages in the yield formation of cereals (wheat, spring triticale), maize, and sugar beet coincides with a depressed development in the yield components. The application of K fertilizer to plants is a simple agronomic practice used to increase crop tolerance to a temporary water shortage. It may be that the improvement of a plant's access to K during mild water-deficiency stress will increase water uptake by the root cells, which in turn increases their osmotic potential and thereby allows extension growth. This growth in turn promotes access to other mineral elements (including nitrogen) and water, which favor plant growth and yield.

Evaluation of industrial wastes as sources of fertilizer silicon using chemical extractions and plant uptake

Abstract: Six inorganic industrial-waste materials (coal fly ash, bauxite-processing mud, steel slag, two samples of air-cooled blast furnace [BF] slag, and one sample of water-cooled BF slag), along with wollastonite, were evaluated as fertilizer-Si sources. Evaluation was carried out by analyzing total and extractable Si fractions in the materials, by incubating them at two rates with a Si-deficient soil and measuring potentially available extractable Si and by measuring yield and Si uptake by two successive rice crops grown in the fertilized soils. Of the waste materials used, fly ash had the highest total Si content (29%) but a negligible quantity was present in extractable forms. Steel slag and bauxite-processing mud had only 5%–7% Si content while BF slags contained 14%–18% Si. All materials, other than fly ash, increased the amount of extractable Si present in the soil. Additions of steel slag and bauxite-processing mud caused greater increases in Si extractability than the air-cooled BF slags while water-cooled BF slag–treated soils contained notably high acid-extractable Si. Because of the alkaline nature of the materials, and their reaction products, there was a positive relationship between extractable soil Si and soil pH. However, an equilibration experiment using NaSiO3 as the Si source confirmed that Si solubility in the soil decreased with increasing pH. Dry-matter yields of rice, at the lower rate of Si addition, were increased by all treatments other than fly ash. The higher rates of steel slag and bauxite-processing mud caused yield depressions. Total Si uptake by rice was increased by all treatments, other than fly ash, and was greater at the higher rate of Si addition. It was concluded that the BF slags are the most effective waste materials as fertilizer-Si sources and that, in slag-amended soils, CaCl2 and NH4 acetate are the most reliable soil-test extractants.

Mechanisms of aluminum‐induced growth stimulation in tea (Camellia sinensis)

Abstract: Beneficial effects of aluminum (Al) on plant growth have been reported for plant species adapted to acid soils. However, mechanisms underlying the stimulatory effect of Al have not been fully elucidated. The aim of this study was to determine the possible contribution of photosynthesis, antioxidative defense, and the metabolism of both nitrogen and phenolics to the Al-induced growth stimulation in tea (Camellia sinensis [L.] Kuntze) plants. In hydroponics, shoot growth achieved its maximum at 50 μM Al suply (24 μM Al3+ activity). A more than threefold increase of root biomass was observed for plants supplied with 300 μM Al (125 μM Al3+ activity). Total root length was positively related to root Al concentrations (r = 0.98). Chlorophyll a and carotenoid concentrations and net assimilation rates were considerably enhanced by Al supply in the young but not in the old leaves. Activity of nitrate reductase was not influenced by Al. Higher concentrations of soluble nitrogen compounds (nitrate, nitrite, amino acids) and reduction of protein concentrations suggest Al-induced protein degradation. This occurred concomitantly with enhanced net CO2-assimilation rates and carbohydrate concentrations. Aluminum treatments activated antioxidant defense enzymes and increased free proline content. Lowering of malondialdehyde concentrations by Al supply indicates that membrane integrity was not impaired by Al. Leaves and roots of Al-treated plants had considerably lower phenolic and lignin concentrations in the cell walls, but a higher proportion of soluble phenolics. In conclusion, Al-induced growth stimulation in tea plants was mediated by higher photosynthesis rate and increased antioxidant defense. Additionally, greater root surface area may improve water and nutrient uptake by the plants.

Macro‐ and micronutrient‐release characteristics of three polymer‐coated fertilizers: Theory and measurements

Abstract: In spite of several published studies we have an incomplete understanding of the ion-release mechanisms and characteristics of polymer-coated fertilizers (PCF). Here we extend current conceptual models describing release mechanisms and describe the critical effects of substrate moisture and temperature on macro- and micronutrient release of three PCF types: Polyon ® , Nutricote ® , and Osmocote ® . Nutrient release was quantified at weekly intervals for up to 300 d from 5°C to 40°C in water and chemically inert sand, substrates that allowed release quantification without confounding effects of ion sorption/desorption. At least two release-timeframe formulations of each PCF type were studied and all products had similar nutrient concentrations to allow isolation of the effect of coating technology. Contrary to several studies, our data and model indicate that there is no significant difference in nutrient-release rates in water and a moist, solid substrate. This means that release rates determined in water can be used to model bio-available nutrient concentrations in moist soil or soilless media where sorption/desorption properties alter concentrations after release. Across all PCF, the nutrients most affected by temperature were typically N, K, B, Cu, and Zn, while the least affected were P, Mg, and Fe. We also found consistent differences among the coating technologies. Osmocote fertilizers released faster than specified at both high and low temperatures. Nutricote had relatively steady release rates over time and a nonlinear response to temperature. Polyon released more slowly than specified but replicate samples were highly uniform.

Cover crop seeding date influence on fall nitrogen recovery

Abstract: Planting cover crops after corn-silage harvest could have a critical role in the recovery of residual N and N from fall-applied manure, which would otherwise be lost to the environment. Experiments were conducted at the University of Massachusetts Research Farm during the 2004–2006 growing seasons. Treatments consisted of oat and winter rye cover crops, and no cover crop, and four cover-crop dates of planting. The earliest planting dates of oat and winter rye produced the maximum biomass yield and resulted in the highest nitrate accumulation in both cover-crop species. The average nitrate accumulation for the 3 years in winter rye and oat at the earliest time of planting was 60 and 48 kg ha–1, respectively. In 2004 where the residual N level was high, winter rye accumulated 119 kg nitrate ha–1. While initially soil N levels were relatively high in early September they were almost zero at all sampling depths in all plots with and without cover crops later in the fall before the ground was frozen. However, in plots with cover crops, nitrate was accumulated in the cover-crop tissue, whereas in plots with no cover crop the nitrate was lost to the environment mainly through leaching. The seeding date of cover crops influenced the contribution of N available to the subsequent crop. Corn plants with no added fertilizer, yielded 41% and 34% more silage when planted after oat and rye, respectively, compared with the no–cover crop treatment. Corn-silage yield decreased linearly when planting of cover crops was delayed from early September to early or mid-October. Corn-ear yield was influenced more than silage by the species of cover crop and planting date. Similar to corn silage, ear yield was higher when corn was planted after oat. This could be attributed in part to the winter-kill of oat, giving it more time to decompose in the soil and subsequent greater release of N, while the rapidly increasing C : N ratio of rye can lessen availability to corn plants. Early plantings of cover crops increased corn-ear yield up to 59% compared with corn-ear yield planted after no cover crop.

Climate‐strategic agriculture and the water‐soil‐waste nexus

Abstract: Adoption of input-responsive varieties enhanced food production during the second half of the 20th century. However, even bigger challenges lie ahead because of the growing societal demands. For example, the global population of 7.2 billion in 2013 is projected to reach 9.2 billion by 2050 and stabilize at 10 billion by 2100. The growing and increasingly affluent population, with preference towards more and more meat-based diet, is likely to jeopardize the finite, fragile, and dwindling soil and water resources which are already under great stress in densely populated countries in Asia and elsewhere. Economic growth and increase in gross domestic product also lead to generation of waste or by-products, along with contamination and eutrophication of water resources. International trade in food/feed products also involves transfer of virtual water, which is a serious issue when water-scarce countries export virtual water to water-endowed countries. The problem is confounded by the present and future climate change driven by the growing energy demands of the carbon civilization. Thus, adaptation to climate change represents both a threat and an opportunity for sustainable development. Adaptive strategies must be sustainable socially and environmentally and advance the Millennium Development Goals, while buffering agroecosystems against extreme climate events (e.g., pedologic, agronomic, and ecologic drought). Thus, recognizing and addressing the water-soil-waste nexus is important to achieving climate-strategic agriculture. Sustainable intensification of agroecosystems, producing more per unit consumption of essential resources, must consider judicious management of hydrological and biogeochemical cycles (C, N, P, S). The soil C pool must be managed and enhanced to offset anthropogenic emissions, and mitigate/adapt to the climate change. The pace of adoption of recommended land use and soil-/plant-/animal-management practices can be kept at par with advances in scientific knowledge through continuous dialogue between scientists on the one hand and policy makers / land managers on the other to translate research data into policy and action plans.

Effect of commercial amino acids on iron nutrition of tomato plants grown under lime-induced iron deficiency

Abstract: This work was supported by AGL2006-04327 project from Ministerio de Educacion y Ciencia (MEC).

How different long-term fertilization strategies influence crop yield and soil properties in a maize field in the North China Plain

Abstract: The impact of fertilization on maize (Zea mays L.) yield and soil properties was investigated in a long-term (> 18 y) experimental field in N China. A completely randomized block design with seven fertilizer treatments and four replications was used. The seven fertilizer treatments were (1) compost (COMP), (2) half compost plus half chemical fertilizer (COMP1/2), (3) balanced NPK fertilizer (NPK), (4–6) unbalanced chemical fertilizers without one of the major elements (NP, PK, and NK), and (7) an unamended control (CK). In addition to maize yield, soil chemical and biological properties were investigated. Compared to the balanced NPK treatment, maize yield from the COMP treatment was 7.9% higher, from the COMP1/2 was similar, but from the NP, PK, NK, and CK treatment were 12.4%, 59.9%, 78.6%, and 75.7% lower. Across the growing season, microbial biomass C and N contents, basal soil respiration, and fluorescein diacetate hydrolysis, dehydrogenase, urease, and invertase activities in the COMP and COMP1/2 treatments were 7%–203% higher than the NPK treatment. Values from all other treatments were up to 60% lower than the NPK treatment. Maize yield is closely related to the soil organic C (OC) and biological properties, and the OC is closely related to various biological properties, indicating that OC is a suitable indicator for soil quality. Our results suggest the most limiting nutrient for improving the yield or soil quality was P, followed by N and K, and balanced fertilization is important in maintaining high crop yield and soil quality. Additionally, increases in OC, N, and biological activities in COMP and COMP1/2 treatments imply that organic compost is superior to the chemical fertilizers tested.

High K+ supply avoids Na+ toxicity and improves photosynthesis by allowing favorable K+:Na+ ratios through the inhibition of Na+ uptake and transport to the shoots of Jatropha curcas plants.

Abstract: This study assessed the relationships between external K+ supply and K+ : Na+ ratios associated with Na+ toxicity in Jatropha curcas. Plants were exposed to increasing external K+ concentrations (6.25, 12.5, 25, 37.5, and 50 mM), combined with 50 mM NaCl in a nutrient solution. Photosynthesis progressively increased as the external K+ : Na+ ratios increased up to 0.75. The increase of photosynthesis and plant dry matter correlated positively with K+ : Na+ in xylem and leaves. The transport rates of K+ and Na+ from roots to xylem and leaves were inversely correlated. These ions presented an antagonistic pattern of accumulation in all organs. Maximum rates of photosynthesis and plant growth occurred with leaf K+ : Na+ ratios that ranged from 1.0 to 2.0, indicating that this parameter in leaves might be a good indicator for a favorable K+ homeostasis under salinity conditions. The higher K+ affinity and selectivity compared with Na+ in all organs associated with higher xylem flux and transport to shoots are essential for maintaining adequate K+ : Na+ ratios at the whole-plant level. These characteristics, combined with adequate K+ concentrations, allow J. curcas to sustain high rates of photosynthesis and growth even under toxic NaCl levels.

Use of meat hydrolyzate derived from tanning residues as plant biostimulant for hydroponically grown maize.

Abstract: Traditional agricultural production systems are evolving towards organic, sustainable, or environmentally friendly systems. Nonetheless, it is important to maintain crop yield and quality. For this purpose, the use of peptide-based products from animal sources in agriculture could be a way to both reduce the disposal of animal-processing residues and decrease the use of mineral fertilizers. The aim of our work was to obtain new insights into the biological effects of meat hydrolyzate (MH) derived from the hydrolysis of tanning residues. Maize (Zea mays L.) was grown hydroponically in a climatic chamber, and 12-d-old plants were treated for 48 h with different concentrations of the MH: 0 (control), 0.01 or 0.1 mL L–1. Both treatments enhanced plant growth and microelement concentrations in maize seedlings and decreased NO, PO, and SO concentrations compared to the control. The faster metabolic conversion of these ions was due to enzyme activities of nitrogen (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and aspartate aminotransferase) and carbon metabolism (malate dehydrogenase, isocitrate dehydrogenase, and citrate synthase). The gene transcription for these enzymes was in line with their activities. The effects of MH could partly be ascribed to endogenous indole-3-acetic acid and partly to amino acids and small peptides detected in the tested compound. This study shows that tanning-process residues can be recycled and used in agriculture.

Silicon uptake by wheat: Effects of Si pools and pH

Abstract: Silicon (Si), although not considered essential, has beneficial effects on plant growth which are mostly associated with the ability to accumulate amorphous (phytogenic) Si, e.g., as phytoliths. Phytogenic Si is the most active Si pool in the soil-plant system because of its great surface-to-volume ratio, amorphous structure, and high water solubility. Despite the high abundance of Si in terrestrial biogeosystems and its importance, e.g., for the global C cycle, little is known about Si fluxes between soil and plants and Si pools used by plants. This study aims at elucidating the contribution of various soil Si pools to Si uptake by wheat. As pH affects dissolution of Si pools and Si uptake by plants, the effect of pH (4.5 and 7) was evaluated. Wheat was grown on Si-free pellets mixed with one of the following Si pools: quartz sand (crystalline), anorthite powder (crystalline), or silica gel (amorphous). Silicon content was measured in aboveground biomass, roots, and soil solution 4 times in intervals of 7 d. At pH 4.5, plants grew best on anorthite, but pH did not significantly affect Si-uptake rates. Total Si contents in plant biomass were significantly higher in the silica-gel treatment compared to all other treatments, with up to 26 mg g(-1) in aboveground biomass and up to 17 mg g(-1) in roots. Thus, Si uptake depends on the conversion of Si into plant-available silicic acid. This conversion occurs too slowly for crystalline Si phases, therefore Si uptake from treatments with quartz sand and anorthite did not differ from the control. For plants grown on silica gel, real Si-uptake rates were higher than the theoretical value calculated based on water transpiration. This implies that Si uptake by wheat is driven not only by passive water flux but also by active transporters, depending on Si concentration in the aqueous phase, thus on type of Si pool. These results show that Si uptake by plants as well as plant growth are significantly affected by the type of Si pool and factors controlling its solubility.

Non-protein thiols and glutathione S-transferase alleviate Cd stress and reduce root-to-shoot translocation of Cd in rice

Abstract: A hydroponic experiment was conducted to investigate the dynamic variations of cadmium (Cd) uptake and transport, non-protein thiols (NPT) and glutathione (GSH) concentrations, glutathione S-transferase (GST) activity and lipid peroxidation under Cd stress in order to clarify the role of NPT and GST in reducing Cd toxicity and translocation in rice (Oryza sativa L.). Cadmium accumulation was initially fast and then slowed down with increasing time of Cd exposure. However, the rice growth inhibition and lipid peroxidation were not intense until 5d after Cd treatment, even though Cd kept accumulating in root and shoot, suggesting that Cd may be effectively detoxified. The concentrations of NPT in root increased gradually until 5d after Cd stress, whereas those in shoot showed no significant changes. The concentration of shoot GSH was progressively enhanced upon Cd treatment, while it gradually declined in root after an initial increase. The GST activity varied similarly in root and shoot, reaching the maximum level on 3rd day, followed by a significant decrease 5 d after Cd application. Significant increases of lipid peroxidation and root-to-shoot translocation on 7th day indicate that the equilibrium in Cd-thiol interaction in rice might be disturbed upon the prolonged Cd exposure. In summary, our results suggest that Cd may be retained and detoxified in rice root through chelation with thiol compounds and subsequent sequestration.

Stimulation of phenolic metabolism by silicon contributes to rice resistance to sheath blight

Abstract: Sheath blight caused by Rhizoctonia solani is a major disease of rice worldwide. Silicon (Si) can enhance rice resistance to sheath blight, but the relation with phenolic metabolism is poorly known. Two rice cultivars with different levels of resistance to R. solani (resistant Teqing and susceptible Ningjing 1) were studied to determine the effects of Si on disease intensity (rated from 0 to 9) and the involvement of phenolic compounds in disease resistance. Variation in the concentrations of phenolics (including total soluble phenolics, flavonoids, and lignin) and in the activities of defense-related enzymes polyphenoloxidase (PPO) and phenylalanine ammonia-lyase (PAL) in rice leaf sheaths was investigated. The results show that Si application reduced sheath-blight disease ratings of Ningjing 1 and Teqing by 2.96 and 0.65, respectively. In uninoculated plants, Si application alone had no significant effects on the concentrations of phenolic compounds or on the activities of PPO and PAL. In inoculated plants, Si application increased phenolics concentrations and PPO and PAL activities only in the susceptible cultivar Ningjing 1. We conclude that Si-induced enhancement of phenolic metabolism contributed to the improved resistance of rice to sheath blight in the sensitive cultivar.

Responses of photosynthesis, chlorophyll fluorescence, and grain yield of maize to controlled‐release urea and irrigation after anthesis

Abstract: Controlled-release urea (CRU) is a new type of urea, which may increase crop nitrogen (N)-use efficiency compared with conventional urea (CU), but the conditions where it outperforms urea are not well defined. A field experiment assessing responses of plant growth and grain yield of maize to CRU and irrigation was conducted on a typical agricultural farm in Shandong, China. Five treatments of the two types of urea (75, 150 kg N ha–1, 0 kg N ha–1) were applied as basal fertilizer when sowing maize, and two water treatments (W0 and W1) were used 23 d after anthesis. Net photosynthetic rate (PN) and chlorophyll concentration as well as leaf-area index (LAI) increased significantly by both CRU and CU application, with the increases being larger in CRU-treated plants than in CU-treated plants at grain filling and maturing stages. CRU significantly enhanced the maximum photochemical efficiency (Fv / Fm), PSII coefficient of photochemical fluorescence quenching (qP), and actual quantum yield of PSII electron transformation (ΦPSII) but decreased the nonphotochemical quenching (NPQ). Cob-leaf N concentration of CRU-treated plants was significantly higher than that of CU-treated plants under no irrigation, but not in the irrigation treatment 30 d after anthesis. Significant positive correlations were found between cob-leaf N concentration and PN both with and without irrigation. Grain yield of maize was significantly higher in the CRU treatment than in the CU treatment under both irrigation conditions. In conclusion, CRU as a basal application appeared to increase the N-use efficiency for maize relative to CU especially by maintaining N supply after anthesis.

Potassium management in tea plantations: Its uptake by field plants, status in soils, and efficacy on yields and quality of teas in China

Abstract: Tea is one of the major cash crops in the tropical and subtropical areas of China. Insufficient potassium (K) supply is an important limiting factor to the productivity as the soils are highly leached and strongly acidic. However, information about effects of K fertilization and application techniques is very limited. This manuscript summarizes results of field experiments investigating K uptake, soil K status, effects and methods of K fertilization in China during the past two decades. The K stocks and uptake were investigated by soil sampling in plantations aged 1, 2, 3, 5, and 10 years. There was no harvest of young shoots, and most K was assigned to frame growth accounting for 59%–61% of the total uptake in the aboveground plant parts of young plantations aged 1–3 years. In plantations (≥ 5 years) such assignment to frame growth became relatively small (7.6%–11.9%) and a major proportion was assigned to young shoots accounting for up to 78% of the total. Analysis of 3396 soil samples taken in 2009–2010 from 54 counties of 16 main tea-producing provinces showed that the exchangeable K (extracted by Mehlich III) in soils averaged 81 mg kg–1 and in about 74% samples were below critical deficient level (100 mg kg–1). The low activity ratio at equilibrium (AR ke) and nonspecific absorbed-K (ΔK0) values of quantity-intensity (Q/I) curves also indicated low status of labile K pools of tea soils. Field experiments at 16 of total 18 sites with black, green, and oolong teas during 1992–2002 showed a significant increase of yield after K application either as potassium sulfate (K2SO4) or potassium chloride (KCl) despite of the largely different initial soil exchangeable K contents, plucking standards, and yield levels among the tea types. The agronomical efficiency of K fertilizers was averaged at 8.8 kg fresh shoots or 1.71 kg tea per kg K fertilizer. The quality of harvested shoots was improved by K-fertilizer application as revealed by increased concentrations of free amino acids, water-extractable dry matter, and total polyphenols. There was little difference in the effects of K as K2SO4 and KCl on yield and quality. Field experiments at six sites evaluating variable K amounts demonstrated that the optimal K doses ranged from 124 to 160 kg K ha–1 y–1 for both K2SO4 and KCl and were little affected by initial soil K contents, tea types, and the yield levels. No privilege of K applications split into three times in tea seasons was observed concerning the risk of leaching in the soils of low cation-exchange capacity and abundant rainfall in the production areas. A single K application as base fertilizer in autumn had similar or better effect. The present studies showed low soil labile K pools, incapable to meet plant K demand for quality tea production, highlighting the importance of K-fertilizer application.

Impact of cattle slurry acidification on carbon and nitrogen dynamics during storage and after soil incorporation

Abstract: Acidification of animal slurry is recommended in order to reduce NH3 emissions, but relatively little is known about the effect of such treatment on C and N dynamics during acidification, storage, and after soil application. A laboratory study was performed, and the CO2 emissions from a high–dry matter slurry (HDM), a low–dry matter slurry (LDM), and the same respective acidified slurries (AHDM and ALDM) were followed during a storage period and after soil incorporation. The N-mineralization and nitrification processes, as well as microbial-biomass activity were also estimated in soil receiving both the acidified and nonacidified materials. We observed a strong CO2 emission during the acidification process, and acidification led to a small increase in CO2 emissions (≈ 11%) during storage of AHDM relative to HDM. No effect of LDM acidification on CO2 emissions during storage was observed. About 30% of C released during storage of AHDM was inorganic C, and for ALDM the C release was exclusively inorganic. Soil application of AHDM and ALDM led to a decrease in soil respiration, nitrification, and microbial-biomass-C values, relative to soil application of HDM and LDM, respectively. Furthermore, it was shown that this effect was more pronounced in ALDM- than AHDM-treated soil. Considering both steps (storage and soil application), acidification led to a significant decrease of C losses and lower C losses were observed from LDM slurries than from HDM slurries.

Nitrogen availability of various biogas residues applied to ryegrass.

Abstract: Biogas plants in Germany are producing an increasing amount of biogas residues to be recycled via agricultural crop production. To test whether the wide range of various substrates used in the anaerobic digestion can affect the chemical composition and nutrient availability, seven biogas residues derived from different substrates were investigated with respect to their N supply to ryegrass. Both the short-term and the long-term N availability were studied in a 309-d pot experiment lasting for five successive growth cycles each starting with a fertilizer application. The organic fertilizers were applied based on an equal amount of ammonium-N (300 mg N per pot) and compared to mineral N from ammonium nitrate of equal dosage. Biogas residues varied greatly in their chemical composition (ammonium-N 0.20% to 0.51%, Ntotal 0.36% to 0.75%, and Corg 1.85% to 4.75% in fresh matter). After the first growth cycle, the N availability of the biogas residues applied based on ammonium-N was at least equal to that from ammonium nitrate. Differences in N offtake after one fertilizer application were negatively correlated to the Corg : Norg ratio of the organic fertilizers. After five successive fertilizer applications, the N utilization of most of the organic fertilizers was increased compared to that of the mineral fertilizer. It is concluded that biogas residues provide plant-available N at least corresponding to their ammonium content and that the accumulation of organic N in soil through repeated application of biogas residues contributes to N release.

Effects of boron excess in nutrient solution on growth, mineral nutrition, and physiological parameters of Jatropha curcas seedlings.

Abstract: Jatropha curcas L. has recently attracted the attention of the international research community due to its potential as a biodiesel crop. In addition, its high resistance to drought and salinity is well known. Under arid and semiarid conditions, boron (B) concentrations in irrigation water can be higher than desired when water from industry, urban areas, or desalination is used. However, the growth and physiological responses of J. curcas plants to B excess in the irrigation water are unknown. Therefore, a greenhouse experiment was conducted to study the effects of B excess in the nutrient solution (0.25, 2, 4.5, and 7 mg L1 B, applied as H3BO3) on plant growth, mineral concentration in the different plant tissues, photosynthesis, water relations, chlorophyll fluorescence, chlorophyll concentration (as SPAD values), and composition of carbohydrates. Plant growth decreased with increasing B concentration in the nutrient solution; growth reduction was higher for roots than for leaves or stems. The B concentration increased in all plant tissues, in the following order: leaf > root > stem. These data indicate that the roots of J. curcas are more sensitive to B toxicity than the leaves and that B has restricted mobility inside these plants, accumulating mainly in the basal and middle leaves via the transpiration stream. Increasing B concentration in leaves decreased the ACO2 and the stomatal conductance, but the leaf water parameters were not affected. The data for chlorophyll concentration and chlorophyll fluorescence indicated that nonstomatal factors were involved in the ACO2 decline, whereas decreases in the parameters of PSII photochemistry due to B toxicity suggest that there was structural damage in chloroplasts. There was also a general tendency for a decrease in nonstructural carbohydrates in all plant tissues, possibly due to the decline in ACO2. With excess B, the concentrations of K and Mg increased in leaves due to a decrease in the growth, while a typical antagonistic effect between B and P was evident from the P concentration decrease in leaves. In summary, J. curcas should be considered a B-sensitive plant, as a leaf B concentration of 1.2 mg (g dw)1 caused a growth decline of approximately 30%.

Humus balancing in Central Europe—concepts, state of the art, and further challenges

Abstract: Humus-balancing methods are simple tools for the assessment of interactions between agricultural land use and soil organic matter (SOM). Aside from this commonality, approaches for humus balancing differ considerably with regard to their specific aim, scope, and methodical approach. The term “humus balance” covers both simple models to quantify SOM change in arable soils, or soil organic C (SOC) change in particular, and models that refer to the optimization of soil productivity in arable soils by calculating organic-fertilizer demand, without quantifying SOM or SOC change. This situation naturally has caused much discussion and misunderstandings. Against this background, the aim of this review is to systematically explore the different methodical approaches to humus balancing in order to contribute to a more sophisticated discussion of this model family, its opportunities, and limitations. As humus balancing has long history as well as special actual relevance in Germany, and, lately Switzerland, we focus on these countries and discuss the different approaches that are presently available and applied there. We argue that humus balances can be roughly categorized into “ecological” and “agronomical” approaches based on their specific concepts and methodology. Ecological humus balances comprise a strong link to quantitative SOM change, while humus balances of the agronomical family refer to the maintenance of soil productivity without a quantitative link to SOM change. Lately, some models have been presented that link the two concepts. However, we identify that humus-balancing methods often are insufficiently validated, partly because the validation of agronomical humus balances is not easily possible without a very comprehensive field-experimental basis. Further, the comparability of different approaches even within the two concept families is low at present, indicating the need for a comparative model evaluation for a proper assessment of the methods.

Soil phosphorus fractions after seven decades of fertilizer application in the Rengen Grassland Experiment.

Abstract: Declining global P reserves require a better understanding of P cycling in soil and related plant uptake. On managed grasslands, application of lime and fertilizer affects not only soil nutrient status, but also plant-species composition of the sward. We examined the P fractionation in the Rengen Grassland Experiment (RGE) on a naturally acid Stagnic Cambisol in the Eifel Mts. (Germany) 69 y after the setup of the experiment. A modified sequential Hedley fractionation was carried out for samples from 30 plots at 0–10 cm depth. Application of inorganic phosphorus fertilizer had diverse effects on inorganic (Pi) and organic P (Po) fractions. Resin-Pi, NaHCO3-Pi, NaHCO3-Po, NaOH-Pi, HCldil-Pi, HClconc-Pi, and HClconc-Po contents increased, while NaOH-Po significantly decreased and residual-P remained unaffected. Strongest enrichment occurred in the HCldil-Pi fraction, probably due to the chemical nature of the basic Thomas slag applied as P fertilizer. Without P fertilization, all fractions except residual-P were more or less depleted. Strong P limitation of the vegetation in the limed treatments without P led to lowered contents also for NaOH-Pi and NaOH-Po. However, NaOH-Po was largest in the Control and even exceeded the respective content in the treatments with P. It remained unclear why species adapted to a low soil P status did not access this P fraction though being P-limited. Published theory on the availability of Hedley P fractions does neither match P exploitation nor P nutritional status of the vegetation in the RGE. Regarding NaOH-Po as stable and HCldil-Pi as moderately labile led to a more realistic evaluation of plant P uptake. Evaluation of P availability on the basis of chemical extractions alone is questionable for conditions like in the RGE. On long-term grassland, plant-species composition has to be taken into account to estimate access of plants to soil P.

Interpretation of lysimeter weighing data affected by wind

Abstract: Weighing lysimeters are valuable devices for measuring water-balance components with high temporal resolution and high accuracy. However, some older lysimeter facilities still operate with lever-arm-counterbalance weighing systems that are sensitive to disturbances, e.g., forces exerted by wind. Filtering and averaging are commonly used for processing noisy raw data. We studied some data of a lever-arm weighing system and performed additional experiments in order to (1) determine the measurement accuracy of the current weighing scheme (facility, and measuring and averaging procedure) regarding wind effects, (2) describe the oscillation behavior, (3) test the mechanical performance of the system, and (4) adapt the averaging procedure with respect to improved interpretation of the weighing data. The measurement accuracy for a wind velocity < 5 m s–1, measured in 10 m height, was ≈ ± 0.4 kg (equivalent to ± 0.14 mm); at a higher wind velocity, the accuracy was three times lower, but there was no linear relationship. Additional experiments showed that the weighing system is oscillating with more or less irregular amplitudes. A loading–unloading experiment delivered proper results of the measured loads. The mechanical system reacted immediately, and no directional effects were found. However, small changes of < 1 kg could hardly be determined due to the oscillations. A time series of raw data measured every 2 s served as basis for improving the averaging method. A moving average from 64 values was computed representing the currently used method, and serving as reference. With this procedure an accuracy of ± 0.38 kg could be reached. Averaging 150 values led to an accuracy of ± 0.28 kg (0.1 mm) for a wind velocity < 5 m s–1.

Purple versus green-leafed Ocimum basilicum: Which differences occur with regard to photosynthesis under boron toxicity?

Abstract: This study was undertaken to investigate how different cultivars of sweet basil (Ocimum basilicum) responded to boron (B) excess. Two purple-leafed and eight green-leafed cultivars were hydroponically grown for 20 d with 0.2 or 20 mg L–1 B in the nutrient solution. Leaf B concentration, gas exchanges, chlorophyll a fluorescence, and oxidative stress were determined at the end of the treatment along with the severity of leaf necrosis. A range of tolerance to B toxicity was found: the green cultivars were more susceptible than the purple-leafed ones characterized by a higher constitutive anthocyanin concentration. In all the genotypes B excess resulted in oxidative stress as determined by accumulation of malondialdehyde by-products (MDA), reduced photosynthesis, and the occurrence of leaf burn. A close correlation was found between leaf B accumulation and oxidative stress, as well as between oxidative stress and the severity of leaf burn. Net photosynthesis (Pn) was reduced due to both stomatal and nonstomatal limitations in the green cultivars whereas the reduction of Pn in the purple leaves was only attributable to stomatal factors. Chlorophyll a fluorescence revealed a decrease in the maximum quantum yield of PSII (Fv/Fm) and in the electron transport rate (ETR) in plants grown with B excess although less reduction was observed in the purple genotypes. The quantum yield of PSII (UPSII) decreased as a result of B toxicity only in the green cultivars. It is concluded that anthocyanins are involved in attenuation of the negative effects of B toxicity.

Potassium-fertilizer management in winter oilseed-rape production in China

Abstract: Optimal potassium (K) fertilization is beneficial for oilseed-rape (Brassica napus L.) yield and quality. However, the discrepancy between the high K demand of winter oilseed rape and low soil fertility and insufficient potassium input has limited the sustainable development of oilseed-rape production. A series of on-farm experiments in the key winter oilseed-rape domains of China was conducted from 2004 to 2010 to evaluate K-fertilizer management for winter oilseed rape. Currently, the average NH4OAc-extractable K content in the 0–20 cm soil layer is 89.1 mg kg–1 indicative of “slight deficiency”. In addition, farmers in China usually fail to use sufficient K fertilizer in oilseed-rape production, the average mineral-potassium-fertilizer input in 2010 being only 35 kg K ha–1, far lower than the recommended rate of potassium for winter oilseed rape. Adequate potassium fertilization significantly raises seed yield. The average yield-increase rate for the major production regions due to K-fertilizer application was 18.5%, and the average K fertilizer–use efficiency 36.1%. Based on the negative correlation between yield response to potassium fertilization and available soil K content, a soil-K-test index was established for winter oilseed rape with a threshold value for NH4OAc-extractable soil K of 135 mg kg–1. When available soil K-content is below this threshold value, more K fertilizer should be applied to achieve high seed yield and to increase soil fertility. The major challenge for K-fertilizer management in winter oilseed-rape production in China will be to guide farmers in the different regions in making reasonable use of K fertilizer through soil K-testing technology in order to maintain both seed yield and soil fertility.

Tonoplast Na+/H+ antiporters of newly developed maize (Zea mays) hybrids contribute to salt resistance during the second phase of salt stress

Abstract: To investigate the role of tonoplast Na+/H+ antiporters (ZmNHX) in salt-stress resistance newly developed maize (Zea mays L.) SR hybrids and cv. Across 8023 were tested under low (50 mM NaCl) and high salinity (200 mM NaCl). Resistance to Na+ toxicity was monitored in terms of shoot growth and number of necrotic leaf spots. At high salinity, the SR hybrids showed better shoot growth than Across 8023. SR 03 and SR 05 had a lower number of necrotic spots per leaf compared to SR 20 and Across 8023. Based on these results, SR 03 and SR 05 were classified as salt-resistant, and SR 20 and Across 8023 as salt-sensitive genotypes. At 200 mM NaCl, the salt-resistant hybrids SR 03 and SR 05 showed a significant upregulation of the tonoplast Na+/H+ antiporter (ZmNHX) in leaves compared with Across 8023 and SR 20. The salt stress–induced increase in transcription of ZmNHX may lead to enhanced tonoplast Na+/H+ antiport in leaves for SR 03 and SR 05. Hence, sequestration of Na+ into leaf vacuoles contributes to salt resistance of these genotypes by protecting the cytoplasm from Na+ toxicity. Relative transcription of ZmNHX in roots was only increased in SR 20, which may explain the efficient Na+ exclusion from shoots of SR 20.