Showing papers in "Advances in Agronomy in 2015"

Chapter One – Mineral–Organic Associations: Formation, Properties, and Relevance in Soil Environments

Abstract: Minerals and organic matter (OM) may form intricate associations via myriad interactions. In soils, the associations of OM with mineral surfaces are mainly investigated because of their role in determining the long-term retention of OM. OM “must decay in order to release the energy and nutrients that drive live processes all over the planet” ( Janzen, 2006 ). Thus, the processes and mechanisms that retain OM in soil are a central concern to very different branches of environmental research. An agronomist may want to synchronize periods of high nutrient and energy release with the growth stages of a crop. An environmental chemist may wish to either immobilize an organic soil contaminant or enhance its decomposition into less harmful metabolites, while climate scientists need to understand the processes that mediate the production of potent greenhouse gases from decomposing OM. Associations of OM with pedogenic minerals (henceforth termed mineral–organic associations (MOAs)) are known to be key controls in these and many other processes. Here we strive to present an overview of the current knowledge on MOAs and identify key questions and future research needs.

Soil Spectroscopy: An Alternative to Wet Chemistry for Soil Monitoring

Abstract: The soil science community is facing a growing demand of regional, continental, and worldwide databases in order to monitor the status of the soil. However, the availability of such data is very scarce. Cost-effective tools to measure soil properties for large areas (e.g., Europe) are required. Soil spectroscopy has shown to be a fast, cost-effective, environmental-friendly, nondestructive, reproducible, and repeatable analytical technique. The main aim of this paper is to describe the state of the art of soil spectroscopy as well as its potential to facilitating soil monitoring. The factors constraining the application of soil spectroscopy as an alternative to traditional laboratory analyses, together with the limits of the technique, are addressed. The paper also highlights that the widespread use of spectroscopy to monitor the status of the soil should be encouraged by (1) the creation of a standard for the collection of laboratory soil spectra, to promote the sharing of spectral libraries, and (2) the scanning of existing soil archives, reducing the need for costly sampling campaigns. Finally, routine soil analysis using soil spectroscopy would be beneficial for the end users by a reduction in analytical costs, and an increased comparability of results between laboratories. This ambitious project will materialize only through (1) the establishment of local and regional partnerships among existent institutions able to generate the necessary technical competence, and (2) the support of international organizations. The Food and Agriculture Organization (FAO) of United Nations and the Joint Research Centre of the European Commission are well placed to promote the use of laboratory and field spectrometers for monitoring the state of soils.

Chapter Four - the challenge of the urine patch for managing nitrogen in grazed pasture systems.

Abstract: Ruminants excrete as much as 70–95% of the nitrogen (N) they consume. The urine patch is the conduit through which much of this N is recycled in grazed pasture systems. This chapter focuses on three key areas: urine patch characteristics and N cycling processes; implications for N cycling at the farm and paddock scale; and strategies available to mitigate N losses from the urine patch. The urine patch N loading rate is a key metric for quantifying and modeling fate of N; yet it is a derived value, relying on estimates of urine volume and N concentration, and the urine patch surface area, all of which are variable. Much is known about N cycling processes in the urine patch but further understanding of N loss, leaching of dissolved organic N, and mineralization–immobilization turnover is needed. Typical values (as a percentage of the deposited urinary N) were estimated as: 13% ammonia volatilization; 2% nitrous oxide emission; 20% nitrate leaching; 41% pasture uptake; 26% gross immobilization. The relative importance of each process is influenced by urine patch characteristics and environmental factors. Models are an important tool for scaling from the individual urine patch to the paddock and farm scale, though accounting for variability in urine patch characteristics, and spatial and temporal distribution, remains a challenge. Many potential management strategies to decrease N loss from the urine patch are still at the proof of concept stage with few actually deployed on the farm. Further research is required to integrate these into farm management systems.

The Use of Biostimulants for Enhancing Nutrient Uptake

Abstract: Fertilizer use in modern agriculture is highly inefficient; much of the applied fertilizer is released into the environment, causing environmental degradation. One way in which fertilizer use can be reduced without damaging plant nutrition is to enhance crop uptake of nutrients through the use of biostimulants. A broad definition of plant biostimulants, including substances sometimes categorized as biofertilizers or biopesticides, is used throughout this review: “Plant biostimulants are substances or materials, with the exception of nutrients and pesticides, which, when applied to plants, seeds, or growing substrates in specific formulations, have the capacity to modify physiological processes in plants in a way that provides potential benefits to growth, development, or stress response.” This definition includes a variety of substances, four of which will be reviewed in this article: seaweed extract, humic substances, amino acids, and plant-growth-promoting bacteria. We will concentrate on the positive effects of biostimulant application on plant nutrient uptake, and the underlying mechanisms, which include positive changes in soil structure or nutrient solubility, root morphology, plant physiology, and symbiotic relationships, will be discussed. Recommendations for future research directions include finding the most promising substances, isolating the active ingredients and clearly demonstrating the mechanisms by which they affect nutrient uptake. The beneficial effects and mechanisms must be consistently demonstrated in greenhouse and field experiments.

Soil Biogeochemistry, Plant Physiology, and Phytoremediation of Cadmium-Contaminated Soils

Abstract: Cadmium (Cd) loading in soil and the environment has been accelerated worldwide due to enhanced industrialization and intensified agricultural production, particularly in the developing countries. Soil Cd pollution, resulting from both anthropogenic and geogenic sources, has posed an increasing challenge to soil quality and food security as well as to human health. Compared with other heavy metals such as copper (Cu) and lead (Pb), Cd demonstrates greater mobility along food chain and in the environment. Cd is harmful to human health and potentially toxic to biota at lower concentrations. Therefore, it is imperative to develop management strategies for control of pollution sources and remediation of contaminated soils. Extensive studies have been conducted in recent years to understand biogeochemical processes of Cd in soils, its cycle in agroecosystems, impacts on soil quality and food security, and the remediation of Cd-contaminated soils. Phytoremediation as an emergent technology has stimulated refreshed interest since it is cost effective and ecofriendly, especially the use of metal hyperaccumulating plants to extract or mine heavy metals from contaminated soils. Progress has been made in the understanding of mechanisms that govern Cd accumulation and detoxification in accumulating plants. This review provides recent progress in soil biogeochemistry and plant physiology of Cd, mechanisms of hyperaccumulation of Cd in plant, remediation strategies including chemical and microbiological enhancement, and optimization of field management practices, in the hope to stimulate more research in the future.

Driver-Pressure-State-Impact-Response (DPSIR) analysis and risk assessment for soil compaction-A European perspective

Abstract: Compaction of subsoil is a hidden but persistent damage that impairs a range of soil functions and ecosystem services. We analyzed the soil compaction issue in the Driver-Pressure-State-Impact-Response (DPSIR) context. The driving force (DPSIR-D) is the farmers' efforts to sustain economic viability. This entails a steady increase in the size and weight of the agricultural machinery (DPSIR-P) exerting the specific pressures on the soil system. Simulations using historical data for agricultural machinery show significant increases in the mechanical stresses exerted on the soil profile during the last five decades. Surveys and comparative measurements (DPSIR-S) in the literature indicate that much of the European subsoil is compacted to critical levels for cropping. This calls for changes in agricultural management (DPSIR-R). Mechanical stresses impact the soil (DPSIR-I) by reducing the volume, dimensions, and interconnections of soil pores. Subsequent impacts on ecosystem services (subtle DPSIR-I aspects) include a decrease in crop production, an impaired soil filtering of pollutants, and the risk of higher greenhouse gas emissions. The natural ability of compacted subsoil to recover is poor. We highlight the need to expand the DPSIR concept to include a risk assessment methodology to identify sustainable management systems. Risk assessment involves the evaluation of the mechanistic cause–effect chain of the compaction process. Measured data as well as modeling indicate that contemporary tires are not able to carry the loads frequently inflicted on wet soil without exerting critical stresses on deep subsoil layers. We suggest the use of online modeling tools that combine existing knowledge. Such tools may also create maps of vulnerable areas from the field to the continent scale. Groups of stakeholders including researchers, farmers and their consultants, and policy-makers need to identify sustainable traffic systems that secure both presently focused ecosystem services as well as nonuse soil values (the bequest for future generations).

Phosphorus Recovery and Reuse from Waste Streams

Abstract: Phosphorus (P) is a macronutrient essential for all living organisms. Regrettably, it is a finite resource since phosphate rock (PR) is the main material used for production of P fertilizers. Globally, the demand for quality PR is escalating due to many factors including increasing human population. Inevitably, the demand for PR will exceed its supply capacity. This condition will be very difficult to manage as living systems have no alternative for P. Moreover, P use efficiency is low; only 15–20% of applied P is used by crops and animals. Globally, the remaining P is shunted into various waste streams. These waste streams include large quantities of effluents rich in P from both municipal and industrial wastewater treatment systems and manure from livestock production. The P present in these waste streams poses a threat to the environment by nutrient enrichment resulting in serious ecological issues such as eutrophication of waterways. However, P in these waste streams, if economically recovered, can contribute to a sustainable management of P resources. This review covers the following aspects: global importance of P as an essential nutrient; efficient and sustainable utilization of P; waste stream production, their suitability for P recovery, and limitations; current and emerging technologies for recovery of P; and the use of recovered P material. Finally, future research needs are identified associated with P recovery from waste streams and reuse in agriculture.

Weedy (Red) Rice: An Emerging Constraint to Global Rice Production

Abstract: Ongoing increases in the human population necessitate that rice will continue to be a critical aspect of food security for the twenty-first century. While production must increase in the coming decades to meet demand, such increases will be accompanied by diminished natural resources and rising production costs that will alter how rice is grown and managed. Such resource constraints are the impetus for the ongoing transition from traditional flooding and transplanting to direct-seeded rice (DSR). However, such a transition can result in an increase in pest pressures, especially weeds. Rice production can be particularly vulnerable to weed competition, with significant yield losses (i.e., >50%) occurring. Among pernicious weeds, weedy (red) rice (Oryza sativa L.) is increasingly recognized as a major constraint in achieving maximum yield in DSR. Weedy rice is congeneric to crop rice with phenotypic similarity; hence, its ability to negatively influence qualitative and quantitative aspects of production is substantial. As rice will continue to serve as a cornerstone for future food security and sustainability, a comprehensive assessment of weedy rice impacts associated with increasing adoption of DSR is both timely and critical. In this chapter, we examine the biological basis for the competitive ability of weedy rice, including its evolution, ecophysiology, and genetics; quantify spatial–temporal shifts in its distribution and spread; and emphasize and outline a number of regional and global management strategies for its detection and control. Lastly, a number of critical research areas are suggested that deserve additional scrutiny with respect to weedy rice management.

Advances in Host Plant and Rhizobium Genomics to Enhance Symbiotic Nitrogen Fixation in Grain Legumes

Abstract: Legumes form symbiotic relationship with root-nodule, rhizobia. The nitrogen (N2) fixed by legumes is a renewable source and of great importance to agriculture. Symbiotic nitrogen fixation (SNF) is constrained by multiple stresses and alleviating them would improve SNF contribution to agroecosystems. Genetic differences in adaptation tolerance to various stresses are known in both host plant and rhizobium. The discovery and use of promiscuous germplasm in soybean led to the release of high-yielding cultivars in Africa. High N2-fixing soybean cultivars are commercially grown in Australia and some countries in Africa and South America and those of pea in Russia. SNF is a complex trait, governed by multigenes with varying effects. Few major quantitative trait loci (QTL) and candidate genes underlying QTL are reported in grain and model legumes. Nodulating genes in model legumes are cloned and orthologs determined in grain legumes. Single nucleotide polymorphism (SNP) markers from nodulation genes are available in common bean and soybean. Genomes of chickpea, pigeonpea, and soybean; and genomes of several rhizobium species are decoded. Expression studies revealed few genes associated with SNF in model and grain legumes. Advances in host plant and rhizobium genomics are helping identify DNA markers to aid breeding of legume cultivars with high symbiotic efficiency. A paradigm shift is needed by breeding programs to simultaneously improve host plant and rhizobium to harness the strength of positive symbiotic interactions in cultivar development. Computation models based on metabolic reconstruction pathways are providing greater insights to explore genotype–phenotype relationships in SNF. Models to simulate the response of N2 fixation to a range of environmental variables and crop growth are assisting researchers to quantify SNF for efficient and sustainable agricultural production systems. Such knowledge helps identifying bottlenecks in specific legume–rhizobia systems that could be overcome by legume breeding to enhance SNF. This review discusses the recent developments to improve SNF and productivity of grain legumes.

Advances and Perspectives to Improve the Phosphorus Availability in Cropping Systems for Agroecological Phosphorus Management

Abstract: Phosphorus (P) is a limiting nutrient for the productivity of many agroecosystems, and the depletion of global mineral P reserves is of concern for global food security. On the other hand, overfertilization with P and its subsequent export through runoff can cause eutrophication of water bodies and natural terrestrial habitats. An important challenge is therefore to develop productive farming systems in which P availability in soils is increased, while reducing mineral P inputs, outputs, and negative off-site impacts. Increasing the P availability in cropping systems requires several approaches including management of soil properties and P amendments, agroecology of cropping systems, and plant breeding. The objective of the present review is to identify new research perspectives in agronomy and emerging strategies to improve the P availability in cropping systems. For this purpose, we explore the following: (1) the use of renewable waste-derived P resources (including crop residues, excreta, struvite, and biochar) to improve P availability, particularly the impacts of applications of such renewable P sources on the chemical properties of the soil, soil organic matter dynamics, soil microbial and rhizospheric activity, and, ultimately, P availability; (2) the effects of multispecies cropping system on P availability, notably the incorporation of the concepts of positive plant–soil feedback on P availability, previously demonstrated in grassland and forest ecosystems, to multispecies cropping systems; and (3) the identification of genetic traits of plant–microorganism relations involved in the tolerance of low-P soils to improve plant breeding outcomes. The challenge for sustainable management of P resources for agriculture is now to reengineer agricultural systems at several scales and to define P management strategies in cropping systems by combining the use of renewable P resources and the management of soil properties, multispecies cropping system, and crop cultivars that increase soil P availability.

Fusion of Soil and Remote Sensing Data to Model Soil Properties

Abstract: Grand global challenges of our time, such as food security and soil security, cannot be met without up-to-date, high-quality, high-resolution, spatiotemporal, and continuous soil and environmental data that characterize soil ecosystems. At local and regional scales, accurate and precise soil assessment is critical for management, soil health, and sustainability. This article presents integration pathways fusing lab- and field-based soil measurements, proximal and remote sensor data, environmental covariates, and/or methods within the framework of the Meta Soil Model which is poised to extend contemporary soil applications. The STEP-AWBH model allows to quantify soil-environmental covariates ( S : soil, T : topography, E : ecology, P : parent material, A : atmosphere, W : water, B : biota, H : human factors) of which numerous can be sensed. We present an in-depth overview of proximal and remote sensor technologies that are used in the realm of digital soil assessment. Specific attention is given to the fusion process of (1) proximal, (2) proximal/remote, and (3) remote sensors to directly sense or predict soil properties. We highlight the promises and perils of sensor-derived proxies that allow inferences on soil properties and their change. From our review it is evident that there is no such single sensor or method that fits all soil applications. In many studies the fusion/integration of data and methods enhance the capabilities to assess specific soil properties. We critically contrast the benefits and constraints of proximal and remote sensing, fusion of soil-environmental data, and integration pathways to mash data and methods into complex soil assessments.

Potential and Challenges of Rainfed Farming in India

Abstract: India ranks first in rainfed agriculture globally in both area (86 Mha) and the value of produce. Rainfed regions in India contribute substantially toward food grain production including 44% of rice, 87% of coarse cereals (sorghum (Sorghum bicolor), pearl millet (Pennisetum glaucum), maize (Zea mays)), and 85% of food legumes, 72% of oilseeds, 65% of cotton, and 90% of minor millets. Overall, the rainfed areas produce 40% of the food grains, support two-thirds of the livestock population, and are critical to food security, equity, and sustainability...

Occurrence, Detection, and Molecular and Metabolic Characterization of Heat-Resistant Fungi in Soils and Plants and Their Risk to Human Health

Abstract: Heat-resistant fungi are often factors causing spoilage of heat-processed products. Contamination of agricultural raw materials is often a result of their contact with soil. Materials contaminated by spores of heat-resistant fungi can be a risk to consumers' health because of toxic metabolites (mycotoxins) produced by these microorganisms. Due to resistance of fungi to high temperatures they are able to survive industry pasteurization process. Therefore, the only way to prevent the growth of these microorganisms in the product is suitable selection of material by conducting tests for the presence of heat-resistant fungi. The use of traditional culture methods is long and, therefore, does not apply in the selection of raw materials for production. However, time is a critical factor in assessing the acceptance or rejection of a given batch of raw material, due to the necessity of processing it fresh, which is very important especially in the case of fruit.

Advances in Structured Light Sensors Applications in Precision Agriculture and Livestock Farming

Abstract: The sustained growth of the world's population in the coming years will require an even greater role for agriculture to meet the food needs of humankind. To improve the productivity and competitiveness of the agricultural industry, it is necessary to develop new and affordable sensing technologies for agricultural operations. This kind of innovations should be implemented in a framework considering the farm, the crops, and their surroundings, with the aim of providing the farmer with information to take better decisions to enhance the production. This is the case of precision agriculture and precision livestock farming. This chapter reviews and discusses the use of structured light sensors in the characterization and phenotyping of crops in orchards and groves, weeds, and animals. As a result of a collaboration between researchers from Spain and Chile, opportunities for this type of sensors have been identified in these countries as examples of South American and European agriculture. In this context, several empirical case studies are presented regarding the use of structured light sensors for flower, fruit, branch, and trunk characterization considering depth and RGB (red-green-blue colors) information in avocados, lemons, apple, and pear orchards. Applications to weed detection and classification as well as to livestock phenotyping are also illustrated. Regarding the presented case studies, experimental and statistical results are provided showing the pros and cons of structured light sensors applied to agricultural environments. Additionally, several considerations are included for the use of this type of sensors to improve the agricultural process.

Weeds of Direct-Seeded Rice in Asia: Problems and Opportunities

Abstract: Rice production symbolizes the single largest land use for food production on the Earth. The significance of this cereal as a source of energy and income seems overwhelming for millions of people in Asia, representing 90% of global rice production and consumption. Estimates indicate that the burgeoning population will need 25% more rice by 2025 than today's consumption. As the demand for rice is increasing, its production in Asia is threatened by a dwindling natural resource base, socioeconomic limitations, and uncertainty of climatic optima. Transplanting in puddled soil with continuous flooding is a common method of rice crop establishment in Asia. There is a dire need to look for rice production technologies that not only cope with existing limitations of transplanted rice but also are viable, economical, and secure for future food demand.Direct seeding of rice has evolved as a potential alternative to the current detrimental practice of puddling and nursery transplanting. The associated benefits include higher water productivity, less labor and energy inputs, less methane emissions, elimination of time and edaphic conflicts in the rice-wheat cropping system, and early crop maturity. Realization of the yield potential and sustainability of this resource-conserving rice production technique lies primarily in sustainable weed management, since weeds have been recognized as the single largest biological constraint in direct-seeded rice (DSR). Weed competition can reduce DSR yield by 30-80% and even complete crop failure can occur under specific conditions. Understanding the dynamics and outcomes of weed-crop competition in DSR requires sound knowledge of weed ecology, besides production factors that influence both rice and weeds, as well as their association. Successful adoption of direct seeding at the farmers' level in Asia will largely depend on whether farmers can control weeds and prevent shifts in weed populations from intractable weeds to more difficult-to-control weeds as a consequence of direct seeding. Sustainable weed management in DSR comprises all the factors that give DSR a competitive edge over weeds regarding acquisition and use of growth resources. This warrants the need to integrate various cultural practices with weed control measures in order to broaden the spectrum of activity against weed flora. A weed control program focusing entirely on herbicides is no longer ecologically sound, economically feasible, and effective against diverse weed flora and may result in the evolution of herbicide-resistant weed biotypes. Rotation of herbicides with contrasting modes of action in conjunction with cultural measures such as the use of weed-competitive rice cultivars, sowing time, stale seedbed technique, seeding rate, crop row spacing, fertilizer and water inputs and their application method/timing, and manual and mechanical hoeing can prove more effective and need to be optimized keeping in view the type and intensity of weed infestation. This chapter tries to unravel the dynamics of weed-crop competition in DSR. Technological issues, limitations associated with DSR, and opportunities to combat the weed menace are also discussed as a pragmatic approach for sustainable DSR production. A realistic approach to secure yield targets against weed competition will combine the abovementioned strategies and tactics in a coordinated manner. This chapter further suggests the need of multifaceted and interdisciplinary research into ecologically based weed management, as DSR seems inevitable in the near future.

Water-Yield Relations and Water Use Efficiency of Maize Under Nitrogen Fertigation for Semiarid Environments: Experiment and Synthesis

Abstract: We examined the main and interactive effects of nitrogen (N) and deficit irrigation (DI) on the yield response factor ( K y ), water use efficiency (WUE), and irrigation water use efficiency (IWUE) of silage maize from a semiarid region of Iran. Experiments were conducted in 2003 and 2004 that included three N fertigation rates (0, 150, and 200 kg N ha −1 N0, N150, and N200, respectively) and four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil water depletion, W1, W2, W3, and W4, respectively). The soil water content measurements showed that most of the water was extracted from the top 60 cm of the soil profile. DI increased WUE for all N fertilizer treatments with the maximum value being observed at the W2 level. The average of the IWUE for the two years of the study showed that the lowest IWUE was 1.38 kg m −3 for the N0W1 treatment, while the highest IWUE was 1.8 kg m −3 for the N200W3 treatment. A linear relationship was observed between evapotranspiration and the total biomass for all N fertilizer levels in 2003 and 2004. The minimum K y to water was obtained from the N0 level as 0.64 in 2003 whereas the maximum K y was recorded from the N200 level as 0.95 in 2004. This reveals that higher N rates application would enhance corn yield sensitivity to water stress. Overall, the sensitivity of the silage maize to water stress was affected by different planting date and nitrogen fertilizer levels. We also discuss emergent trends in water and nutrient management in light of the increased need for food security in the face of changing climate and growing populations.

Management-Induced Changes to Soil Organic Carbon in China: A Meta-analysis

Abstract: Soil carbon (C) sequestration is an environmentally friendly and efficient strategy to offset emissions of greenhouse gases and mitigate climate change. However, inappropriate farming practices can deplete soil organic carbon (SOC) stock and degrade soil quality. Thus, we conducted a meta-analysis to assess and identify the effects of improved farming practices on SOC sequestration in China by compiling a data set of 83 studies. The results indicated that SOC concentration and stocks at 0–30 cm depth significantly increased by 1.00 ± 0.26 g kg−1 and 0.97 ± 0.24 Mg ha−1 when plow tillage with residue removal was converted to no-till with residue retention (NT); 1.11 ± 0.21 g kg−1 and 2.09 ± 0.46 Mg ha−1 when no fertilization was changed to chemical fertilization (CF); and 1.99 ± 0.62 g kg−1 and 3.09 ± 0.99 Mg ha−1 when CF was changed to manure application (MF) (P < 0.05), respectively. However, increases in SOC were primarily observed in the surface layer and decreased with soil depth. Therefore, the adoption of NT and MF in conjunction with CF is an effective strategy to enhance SOC stock in the surface layer. Further, in single-crop farming regions, the effects are more significant at 0–10 cm depth; and the new equilibrium can occur within 11–20 years after the adoption of NT. In double-crop farming regions, conversion to MF enhanced the SOC at 0–20 cm depth over 16 years. Additional research is warranted to credibly assess the rates of residue and manure input, soil “C saturation,” and soil type on the potential SOC sink capacity in China's croplands.

Gypsum Soils—Their Morphology, Classification, Function, and Landscapes

Abstract: Gypsum soils are both a problem and a puzzle, which is precisely why they deserve attention. Gypseous (high-gypsum) soils generally occupy sparsely populated land with minimal land use intensity in arid and semiarid climates. Gypsum content in agricultural soils results in restricted water and nutrient retention and the potential for dissolution piping, primarily in response to irrigation. The corrosive effects of gypsum soils on concrete, metal, and building materials are also problematic. On the other hand, understanding the genesis and function of gypsiferous (low-gypsum) and gypseous soils is interesting and challenging, and our grasp of processes involved in the formation and behavior of these soils is critical for proper management for agricultural, rangeland, engineering, and construction purposes. The objective of this review was to examine the physical and chemical properties of gypsum and the impacts of these properties in the soil environment. The particular properties that gypsum presence imparts to soils affect soil development, including soil morphology. Accumulations of pedogenic gypsum influence water-holding capacity, nutrient and water availability for plants, root growth, and the standard concepts of soil texture and rupture resistance. Gypsum precipitation is also affected by the presence of more soluble salts. The development of physicochemical models that explain the formation and function of gypsiferous and gypseous soils is necessary if we hope to properly manage and maintain these unusual soils and their landscapes.

Biologically regulated nutrient supply systems: compost and arbuscular mycorrhizas - a review

Abstract: To achieve global food security, we will need to produce more food, and do so in an environmentally sustainable manner. Inorganic fertilizers have been instrumental in increasing food production, but with some fertilizers becoming increasingly scarce and expensive, we also need to consider other options for providing agricultural plants with nutrients. To this end, there has been increased interest in the potential to make better use of the nutrients tied up in organic matter; composts are an example of this, and are the focus of this review. Plant nutrient acquisition can be enhanced through the formation of arbuscular mycorrhizas (AM). The purpose of this review is to explore interactions between compost and AM, with an emphasis on the impacts of compost addition and formation and functioning of AM. Based on available literature, it is clear that the application of compost either has a positive or neutral effect on the formation of the symbiosis, and that dual application of compost and arbuscular mycorrhizal fungi (AMF) provides clear benefits to plants in terms of growth and nutrition. There is also emerging evidence that dual application also provides benefits in terms of soil structure. Taken together, the conclusion of this review is that the biologically regulated nutrient supply systems based on compost and AM are compatible.

Nitrogenous gas emissions from soils and greenhouse gas effects.

Abstract: The Haber–Bosch process for synthesizing fertilizer nitrogen (N) is among the most important modern discoveries because it has enabled us to grow enough food for several billion more of us. At the same time, however, profusion of added “reactive” N has become a prominent ecological threat, globally, because a large fraction of applied N is lost from agricultural ecosystems. Nitrogen added to agricultural soils, in organic forms or as synthetic N fertilizers, has one of four fates; it can be assimilated by plants, lost to surface- or groundwater, retained in the soil, or lost to the atmosphere. The last of these is particularly worrisome because of links to climate change and other threats to the biosphere. Our aim is to summarize briefly the processes of atmospheric N emissions to the air from agricultural ecosystems, and to consider how management practices might reduce those emissions. Nitrogen gases emitted from soil emanate from naturally occurring biological processes regulated largely by three interactive factors: substrate availability, aeration, and temperature. Although these factors are partly dictated by weather and intrinsic soil properties, they are also influenced by management so that emissions can be heavily influenced by practices imposed on the land. Variables to consider in devising systems with reduced emissions include: forms, rate, and timing of fertilizer; tillage and residue management; crop rotation, including the use of legumes; and manuring practices. All of these need to be considered together to devise systems, tuned to local conditions, which not only reduce emissions but also meet growing demands for agricultural yields. Developing such systems, based on holistic understanding from many disciplines, is now critical to sustain the long-term productivity and vitality of our ecosystems.

Advances in Using Soft X-Ray Spectroscopy for Measurement of Soil Biogeochemical Processes

Abstract: Light elements are particularly important in biogeochemical processes. These include organic matter components and macronutrients (C, N, O, S, P), micronutrients (Na, Mg, K, Mg), mineral elements (Si, Al), and transition metals. Determining the chemical speciation of these light elements in environmental samples is important for understanding bioavailability, decomposition, contamination mobility, and nutrient cycling. Soft X-ray absorption spectroscopy is a useful tool available to probe the chemistry of atoms important in biogeochemical processes. X-ray absorption spectroscopy (XAS) probes the local bonding and coordination environment of these elements in whole samples. Bulk XAS techniques permit for high throughput, the study of whole soils, and high sampling density. These analyses are complementary to X-ray transmission microscopy techniques which are limited by low throughput, thin particles ( Despite these important applications, bulk soft XAS has not been extensively applied to environmental samples until recently. The primary reasons for this gap is the lack of beamline endstations that are suitable for “dirty” samples and the technical challenges related to acquiring and normalizing spectra from dilute samples. Many of these technical challenges have now been overcome through the development of energy-resolving detectors, proper detector positioning, and development of liquid cell applications. Technical developments and recent applications will be presented, showing how bulk soft X-ray XAS is now positioned to contribute significantly to advancing the characterization of soils and environmental samples.

Climate Change Effects on the Suitability of an Agricultural Area to Maize Cultivation: Application of a New Hybrid Land Evaluation System

Abstract: Climate change is likely to have a major impact on agricultural production in Mediterranean regions, due to higher temperatures and lower water availability for irrigation. A Hybrid Land Evaluation System (HLES) is proposed allowing a comparison between plant demands on the one hand and estimated future temperatures and soil water regimes on the other. A storyline is followed for each plant species hybrid and each soil mapping unit in the area to be studied, starting with step 1: evaluation of thermal conditions, followed by step 2: a traditional empirical land evaluation procedure identifying limiting features that are not covered by crop simulation models (such as flooding, surface stones, salt). Step 3 applies the quantitative Soil–Water–Atmosphere–Plant (SWAP) model and calculates soil water regimes and associated productions, at 100%, 80%, and 60% hypothetical irrigation water availability. HLES was applied in the Destra Sele area in Italy, comparing two climates: “reference” (1961–1990) and “future” (2021–2050), studying 11 maize hybrids and showing that in future, 6 hybrids suffered severely at 80% water availability and 7 could not meet requirements at 60%. HLES allows a proactive approach to future water allocation issues and provides data for genetic modification studies in terms of defining hydrological conditions for sites of native plants and for areas where new hybrids are to be introduced. HLES presents options, to be explored in close interaction with users, rather than one-way judgments.

Climate-Change Effects on Soils: Accelerated Weathering, Soil Carbon, and Elemental Cycling

Abstract: Climate change (i.e., high atmospheric carbon dioxide (CO 2 ) concentrations (≥400 ppm); increasing air temperatures (2–4 °C or greater); significant and/or abrupt changes in daily, seasonal, and interannual temperature; changes in the wet/dry cycles; intensive rainfall and/or heavy storms; extended periods of drought; extreme frost; heat waves and increased fire frequency) is and will significantly affect soil properties and fertility, water resources, food quantity and quality, and environmental quality. Biotic processes that consume atmospheric CO 2 and create organic carbon (C) that is either reprocessed to CO 2 or stored in soils, are the subject of active current investigations with great concern over the influence of climate change. In addition, abiotic C cycling and its influence on the inorganic C pool in soils is a fundamental global process in which acidic atmospheric CO 2 participates in the weathering of carbonate and silicate minerals, ultimately delivering bicarbonate and Ca 2+ or other cations that precipitate in the form of carbonates in soils or are transported to the rivers, lakes, and oceans. Soil responses to climate change will be complex, and there are many uncertainties and unresolved issues. The objective of the review is to initiate and further stimulate a discussion about some important and challenging aspects of climate-change effects on soils, such as accelerated weathering of soil minerals and resulting C and elemental fluxes in and out of soils, soil/geo-engineering methods used to increase C sequestration in soils, soil organic matter (SOM) protection, transformation and mineralization, and SOM temperature sensitivity. This review reports recent discoveries and identifies key research needs required to understand the effects of climate change on soils.

Models, developments, and perspectives of mutual legume intercropping

Abstract: This paper presents the current state of our knowledge of mutual legume intercropping, with an emphasis on its utilization in continental and Mediterranean climates. Its novelty is primarily reflected in the carefully designed schemes for two main forms of mutual legume intercropping. The first one is establishing perennial forage legumes, such as red clover, alfalfa, and sainfoin, with annual legume, such as pea, where the latter acts as a bioherbicide and concurrently contributes to the total forage yield in the first cut of the former. Another form is intercropping annual legumes with each other respecting the same time of sowing, that is, in fall or in spring, similar growth habit, especially stem length, time of maturity for cutting or harvest, and that one component has good standing ability and supports the other one that is susceptible to lodging. Since the prominently pioneering character of this research, most of the presented results, both published and unpublished, shown here for the first time, deal with forage and grain yield and its economic reliability in the form of land equivalent ratio, since this would surely be of the primary interest to the farmers to get introduced with. The first and rather advanced efforts have also been made in the physiology, anatomy, and biotic stress of both forms of mutual intercropping schemes. We anticipate that, together with further research in the said fields along with underground aspects, will make mutual legume intercropping one of the most promising answers for protein-rich food and feed worldwide.

Using Functional Traits to Assess the Services Provided by Cover Plants: A Review of Potentialities in Banana Cropping Systems

Abstract: Cover plant-based cropping systems have gained considerable attention over the last few years because of the recognized benefits of increasing the diversity of agrosystems to sustain services other than those pertaining to production. While agronomical tools and methods to assess these services in multispecies plant communities barely exist, trait-based approaches, originally developed in the field of comparative functional ecology, provide an appropriated framework to study the effects of plant diversity on agrosystems. The aim of this article is to discuss how a trait-based approach can be used to assess the services delivered in cover plant-based cropping system. We focus on semiperennial cropping systems based on cover plants, exemplified by the banana cropping systems. These systems are described in a first section to identify the services targeted. A second section, based on a literature survey, analyzes the processes associated with each service and identifies related effect traits of cover plants. A shortlist of markers to be used to assess agrosystem processes is proposed and hypothesis on trade-offs and synergies among services are formulated. In a third section, issues related to the scaling-up from plant traits to the services delivered by plant agricultural communities are discussed. Such an approach, originated in the field of ecology, appears highly promising to tackle agronomic issues and its application to agrosystems constitutes a challenging test of their genericity. It raises specific questions and stresses the need for new methodological developments, which could be part of a research agenda at the interface between the two disciplines.

Climate Change: Implications for Stakeholders in Genetic Resources and Seed Sector

Abstract: The characteristic of climatic change is increase in the frequency of extreme events that are likely to decrease crop yield. The geographic areas that are currently most food-insecure are likely to be most affected by changing climates. Climate change is likely to affect all dimensions of crop production. Agricultural crop production depends upon the timely availability of good-quality seeds in adequate quantity at affordable prices to the farming communities. Genetic diversity and breeding for improved stress-tolerant genotypes are key elements in tackling climate change. Plant genetic resources (PGRs) are important sources for developing new and improved varieties. The loss of these genetic resources due to climate change will deprive source of diversity and tolerance. Currently, more emphasis has been placed for ex situ conservation, while equally if not more urgency is required to conserve the PGRs in in situ. At present, a number of international agreements are enforced for germplasm exchange and utilization. Some of the important methods to develop and disseminate new cultivars include breeding new crop varieties for wider adaptation under adverse climatic conditions using both classical and modern approaches and seed production through participatory approaches. Participatory breeding programs have successfully led to the development and dissemination of varieties in cereals. Seed industry plays an important role in increasing productivity of crops. The adverse effect of climate change on the seed industry can be minimized by developing efficient seed management systems: breeding, seed production, seed certification, and seed trade. Some efficient systems include adjustment of crop calendars for quality seed production, management of pollinators, strengthening hybrid seed production, postharvest management of seed, seed treatment technologies, seed processing, and seed storage. For faster and timely development, partnerships (public and private) at various levels (regional and international) are crucial. There is an urgent need to strengthen both formal and informal seed systems including characterization of environment to find suitable geographic regions for quality seed production. For seed certification, harmonization of various international seed certification schemes/programs and seed testing procedures are essential. This will also help in efficient and safe movement of seed. To influence seed trade, the effective management of intellectual property rights, sanitary and phytosanitary certificates in addition to management of trade barriers, are all of prime importance for growth of the seed industry. In both developed and developing nations, public investments in plant breeding and seed industry are on the decline. This trend needs to be reversed by emphasizing the need to increase research funding to all stakeholders of genetic resources and seed industry to develop strategies to mitigate the negative impacts of climate change on agricultural systems.

Chapter four - weed problems, ecology, and management options in conservation agriculture: issues and perspectives.

Abstract: The unsustainable exploitation of the inelastic resources for farming has led to a widespread degradation of soil resources, which has forced us to rethink our food production strategies into conservation agriculture (CA). It would be difficult to slow down the intensive-production process keeping in view, the demographic pressure. The present-day systems are posing challenges to land, water, and atmosphere, besides the biodiversity. CA involves minimal disturbance of the land, coupled with good agronomic principles such as crop residue management and crop rotation, with the application of chemicals for weed management. With a view to sustainable development in agriculture, CA is a concept trying to reconcile ecology, economy, and performance. Tillage is practiced since ages, for the preparation of field and making weed-free conditions and is an integral component of traditional agricultural systems. However, soil erosion was inevitable. The focal theme of CA revolves around reducing tillage operations. From a weed management point of view, soil tillage brought buried seeds to the upper layer and stimulated their germination and the maintenance of crop residues hampered the herbicide efficacy. However, there are reports of shift in weed population due to the adoption of CA as compared to the conventional agricultural practices posing a formidable challenge to the CA concept. The interaction of weed–crop system becomes too complex. Reduced tillage and zero tillage allowed seed to stay on the surface so that they become prey to the predators. The crop/cover crop residue may also release some chemicals, which may also reduce weed seed germination process. Understanding the weed seed ecology and weed ecology could aid in devising appropriate management options for successful implementation of CA. An integrated management encompassing selection of appropriate crop cultivar and cropping system coupled with CA principles would aid in the management of weeds. Understanding weed seed predation would add value to the management issues. Herbicide resistance need to be given due attention for chemical weed management.

Wetland Restoration and Creation for Nitrogen Removal: Challenges to Developing a Watershed-Scale Approach in the Chesapeake Bay Coastal Plain

Abstract: Concern for the health of the Chesapeake Bay and the establishment of the Bay Total Maximum Daily Load have led to growing interest in restoring and creating wetlands to mitigate agricultural nitrogen inputs. All Bay states have included wetland restoration in their watershed implementation plans (WIPs) to help meet their required reduction in nitrogen loading. In agricultural areas of the coastal plain, efforts to develop a watershed-scale approach to siting and designing wetlands have been met with considerable challenges. Nitrate loss is primarily attributed to base-flow conditions, and groundwater flow is multidimensional and highly variable, so accounting for nitrate transport connectivity between agricultural N source areas and potential wetland restoration areas is difficult. Socioeconomic and political challenges also constrain implementation. Our ability to account for subsurface connectivity may be improved with better assessment of hydrologic connectivity in areas with artificial drainage, catchment-scale studies of hydrogeomorphic predictions of hydrologic connectivity, and improved use of geospatial data. A coordinated monitoring program would improve our ability to estimate wetland nitrogen removal efficiencies across environmental and management conditions. The addition of a requirement that water quality should be an explicit objective of restorations included within WIP accounting would avoid the inclusion of projects with minimal water quality benefits. Research is also needed on farmer attitudes in the Chesapeake Bay watershed toward wetlands for water quality protection. These proposed actions would improve our ability to understand and implement wetland restoration as a component of our response to meet water quality objectives.

Bacterial Diseases of Crops: Elucidation of the Factors that Lead to Differences Between Field and Experimental Infections

Abstract: Diseases caused by plant pathogenic bacteria have attained great concern worldwide as they are responsible for severe economic losses throughout the cultivated areas. Although studies performed in experimental conditions have provided many new insights into chemical and molecular signaling between plants and bacterial pathogens during pathogenesis, little is known about the factors that interact in natural field conditions. In particular, a wide gap exists between these two systems in terms of disease occurrence and severity. This review attempts to highlight the possible reasons that make natural field conditions different from the experimental ones, which might be useful to bridge the current gap and to facilitate the development of adequate control measures.

Hydrological Aspects of Arsenic Contamination of Groundwater in Eastern India

Abstract: Arsenic in the Bengal Delta has been the topic of discussion for more than a decade since 73% of the population (more than 140 million people) are under deep stress for locating arsenic-free drinking water. Most of this arsenic is geogenic, having its source from the Himalayan metamorphic facies, and is carried down by major river systems and thereby accumulating on the fluvio-deltaic plains to the southeast. All the states on this path are to some extent have depicted the presence of arsenic in the subsurface groundwaters. Currently, there are two major pathways for ingesting arsenic: (1) by the drinking water; and (2) by the food chain. Various scales of health effects from skin lesions to major cancer outbreaks have been located distinctively and pathologically in about 43% of the affected population. Irrigation practices have exacerbated the lateral extent of high arsenic in this region. Secondary natural minerals Fe and Mn oxyhydroxides seem to adsorb both the valences of arsenic and, in the presence of labile organic carbon as in dissolved organic matter, help in releasing the arsenic into the groundwaters. Shallow to intermediate depth-reducing aquifers within the Holocene floodplains are the most contaminated and range from −1 . The Bengal Basin, within a few meters of sea level, has repercussions from infiltrating saline seawater, and the impacts of climate change makes the problem worse in this region. Switching groundwater wells, harvesting rainwater, and household small-scale filtration systems, are the three most effective remediation mechanisms known to the people of the Bengal Delta.