Pasture Crops Research Articles

Productivity and carbon footprint of perennial grass–forage legume intercropping strategies with high or low nitrogen fertilizer input

A three-season field experiment was established and repeated twice with spring barley used as cover crop for different perennial grass-legume intercrops followed by a full year pasture cropping and winter wheat after sward incorporation. Two fertilization regimes were applied with plots fertilized with either a high or a low rate of mineral nitrogen (N) fertilizer. Life cycle assessment (LCA) was used to evaluate the carbon footprint (global warming potential) of the grassland management including measured nitrous oxide (N2O) emissions after sward incorporation.Without applying any mineral N fertilizer, the forage legume pure stand, especially red clover, was able to produce about 15tabovegrounddrymatterha−1year−1 saving around 325kgmineralNfertilizerha−1 compared to the cocksfoot and tall fescue grass treatments. The pure stand ryegrass yielded around 3t DM more than red clover in the high fertilizer treatment. Nitrous oxide emissions were highest in the treatments containing legumes. The LCA showed that the low input N systems had markedly lower carbon footprint values than crops from the high N input system with the pure stand legumes without N fertilization having the lowest carbon footprint. Thus, a reduction in N fertilizer application rates in the low input systems offsets increased N2O emissions after forage legume treatments compared to grass plots due to the N fertilizer production-related emissions. When including the subsequent wheat yield in the total aboveground production across the three-season rotation, the pure stand red clover without N application and pure stand ryegrass treatments with the highest N input equalled. The present study illustrate how leguminous biological nitrogen fixation (BNF) represents an important low impact renewable N source without reducing crop yields and thereby farmers earnings.

Carbon and nitrogen cycling in an integrated soybean-beef cattle production system under different grazing intensities

Abstract:The objective of this work was to evaluate the effect of grazing intensity on the decomposition of cover crop pasture, dung, and soybean residues, as well as the C and N release rates from these residues in a long-term integrated soybean-beef cattle system under no-tillage. The experiment was initiated in 2001, with soybean cultivated in summer and black oat + Italian ryegrass in winter. The treatments consisted of four sward heights (10, 20, 30, and 40 cm), plus an ungrazed area, as the control. In 2009-2011, residues from pasture, dung, and soybean stems and leaves were placed in nylon-mesh litter bags and allowed to decompose for up to 258 days. With increasing grazing intensity, residual dry matter of the pasture decreased and that of dung increased. Pasture and dung lignin concentrations and C release rates were lower with moderate grazing intensity. C and N release rates from soybean residues are not affected by grazing intensity. The moderate grazing intensity produces higher quality residues, both for pasture and dung. Total C and N release is influenced by the greater residual dry matter produced when pastures were either lightly grazed or ungrazed.

Statistical methods for analysis of multi-harvest data from perennial pasture variety selection trials

Variety selection in perennial pasture crops involves identifying best varieties from data collected from multiple harvest times in field trials. For accurate selection, the statistical methods for analysing such data need to account for the spatial and temporal correlation typically present. This paper provides an approach for analysing multi-harvest data from variety selection trials in which there may be a large number of harvest times. Methods are presented for modelling the variety by harvest effects while accounting for the spatial and temporal correlation between observations. These methods provide an improvement in model fit compared to separate analyses for each harvest, and provide insight into variety by harvest interactions. The approach is illustrated using two traits from a lucerne variety selection trial. The proposed method provides variety predictions allowing for the natural sources of variation and correlation in multi-harvest data.

The Awareness of Palm Trees Farmers in the uses of Treated Wastewater in Irrigation

The primary purpose of the study was to determine the awareness of Palm trees farmers toward the uses of wastewater in Palm trees irrigation. The population size of the study was 304 farmers. Questionnaire were reviewed for content and face validity by a panel of experts from department of agricultural extension at the College of Food and Agricultural Sciences, King Saud University . A three point Likert -type scale was used. Cronbach’s alpha coefficient was found to be 0.85, which indicated the internal consistency of the scale. Findings were that: 98% of the farmers used treated wastewater in irrigating Palm trees, 54% of farmers irrigate fruits trees and 40% of farmers irrigate pasture crops with treated water. Seventy eight percent of farmers used flood irrigation, 44% of farmers do not known that they should not collect fruits that fall on the ground when using sewage .Nearly 41% of farmers do not known that they should stop irrigation with treated wastewater one week before harvesting. Significant differences at the level of 0.05 were detected in means of farmers in different levels in age, education, occupation, and experiences. Farmers with higher level of education, more experiences and older in age are more aware of health precautions and technical and laws of wastewater. It recommended that an extension programs be implement to raise awareness of farmers to reduce the risks when using wastewater in agriculture.

Summer Blight of White Clover (Trifolium repens) Caused by Rhizoctonia solani AG-1-IB in China.

White clover (Trifolium repens), also known as Dutch clover (family Fabaceae), is an herbaceous, perennial plant, widely planted as pasture crop and occasionally used as lawn plant. From June to September in 2012 and 2013, approximately 5 to 8% of the plants as garden lawn were infected in the areas surveyed in Tonghua County, Jinlin Province. Ash green and water-soaked lesions appeared initially on the petiole and leaves. Subsequently, petioles collapsed with soft watery rot followed by collapse of leaves and eventually the entire plant. Aerial hyphae appeared on all the infected parts, followed by production of light brown to brown sclerotia. Seven isolates with the morphological characteristics of Rhizoctonia solani Kühn were isolated from symptomatic petioles and leaves which were surface disinfested in 70% alcohol for 30 s and 0.5% sodium hypochlorite for 1 min and plated on potato dextrose agar (PDA). Hyphal tips were transferred to a fresh plate of PDA and the cultures were examined for morphological characters microscopically. Mycelia of all isolates were branched at right angles with a septum near the branch and a slight constriction at the branch base. Hyphal cells were determined to be multinucleate when stained with 1% safranin O and 3% KOH solution (1) and examined at 400× magnification with a microscope. The internal transcribed spacer (ITS) region of the nuclear rDNA was amplified by using the primers ITS4 and ITS5 (2). The ITS sequences of isolates BSYJ14 (GenBank Accession No. HF678123), BSYJ31 (HF571130), BSYY21 (HF678126), and BSY22 (KC572140) exhibited 100% identity with that of R. solani AG 1-1B (AB122138 and HQ185364). ITS sequences of another three isolates, BSYJ11 (HF678122), BSYJ32 (HF678125), and BSYJ12 (HF678121) exhibited 99% identity with the ITS sequence of R. solani AG 1-1B. Pathogenicity tests were performed on healthy, potted T. repens. Five potted plants were inoculated at the base of the petiole with a 0.6-cm diameter mycelial plug from 3-day-old PDA cultures for each isolate, and the inoculation sites were covered with moistened sterile absorbent cotton. Another five potted plants were inoculated with sterile PDA plugs as controls. All plants in the experiments were covered with plastic bags and kept in a greenhouse at 20 to 25°C for 72 h, then the plastic bags were removed. After 5 to 7 days, the symptoms of watery rot were observed on petioles and leaves of all plants inoculated with these isolates, while control plants remained healthy. R. solani AG 1-IB was re-isolated from all plants inoculated with the isolates. The isolates were confirmed by morphological characteristics of the hyphae and hyphal fusions with the original isolates. The pathogenicity test was carried out twice with similar results. R. solani has been reported to cause root rot on T. pratense in northwestern China (4) and summer blight on T. pratense in Japan (3). To our knowledge, this is the first report of R. solani AG 1-IB causing summer blight on T. repens in China.

The influence of land use and management on soil carbon levels for crop-pasture systems in Central New South Wales, Australia

Changes in land use and management have been proposed as a way to increase soil organic carbon (SOC) in crop and pasture systems. Some of the proposed activities to improve SOC are the introduction of pasture phases in cropping systems, stubble retention, no-till cropping, improved fertilisation, introduction of more productive pasture species and grazing management. There is also growing interest in novel farming systems, such as pasture cropping (intercropping cereal crops with established perennial pastures), which may improve SOC. However, there have been few broad scale surveys to determine whether these land management changes have an impact on commercial farms. In this study, comparisons of land use were established for mixed farming and pasture cropping systems in the slopes region (average annual rainfall: 500–650mm) and for cropping and pasture in the plains region (average annual rainfall: 300–500mm) of Central West NSW, Australia. The survey aimed to determine the difference in SOC stocks (Mg C ha−1) and the composition of three soil organic carbon fractions (particulate – POC, humus – HUM and resistant – ROC). The influences of management actions and pasture composition were also assessed across pasture and cropping land uses. Cropping systems had lower SOC stocks in the soil than pasture systems in each region, but pasture cropping was not different from perennial pasture. Generally, there were larger differences in the POC due to land use and management than the other SOC fractions. Management practices in cropping systems explained greater variability in SOC than in pastures. For cropping systems, higher amounts of P fertiliser were associated with higher SOC, POC and ROC while higher amounts of N fertiliser were associated with lower SOC, POC and ROC. For pastures, the proportion of bare ground was associated with lower SOC and POC. These associations indicate there is an opportunity to increase SOC by converting cropping land to permanent pasture, increasing the frequency of pasture phases, changing crop fertiliser regimes and reducing bare ground in pastures, but further work is needed to verify the causality behind these associations.

Characterization of Soil Organic Matter in Aggregates and Size-Density Fractions by Solid State 13C CPMAS NMR Spectroscopy

Understanding the changes in soil organic matter (SOM) composition during aggregate formation is crucial to explain the stabilization of SOM in aggregates. The objectives of this study were to investigate (i) the composition of SOM associated with different aggregates and size-density fractions and (ii) the role of selective preservation in determining the composition of organic matter in aggregate and size-density fractions. Surface soil samples were collected from an Alfisol on the Northern Tablelands of NSW, Australia, with contrasting land uses of native pasture, crop–pasture rotation and woodland. Solid-state 13C cross-polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy was used to determine the SOM composition in macroaggregates (250–2000 μm), microaggregates (53–250 μm), and <53-μm fraction. The chemical composition of light fraction (LF), coarse particulate organic matter (cPOM), fine particulate organic matter (fPOM), and mineral-associated soil organic matter (mSOM) were also determined. The major constituent of SOM of aggregate size fractions was O-alkyl carbon, which represented 44–57% of the total signal acquired, whereas alkyl carbon contributed 16–27%. There was a progressive increase in alkyl carbon content with decrease in aggregate size. Results suggest that SOM associated with the <53-μm fraction was at a more advanced stage of decomposition than that of macroaggregates and microaggregates. The LF and cPOM were dominated by O-alkyl carbon while alkyl carbon content was high in fPOM and mSOM. Interestingly, the relative change in O-alkyl, alkyl, and aromatic carbon between aggregates and SOM fractions revealed that microbial synthesis and decomposition of organic matter along with selective preservation of alkyl and aromatic carbon play significant roles in determining the composition of organic matter in aggregates.

Variability in germination behaviour ofPaspalum dilatatumPoir. seeds is genotype dependent

AbstractDallisgrass (Paspalum dilatatumPoir.) is a warm‐season grass, native to South America. Its adoption as a pasture crop has been hindered by low seed germination and slow establishment. However, variability in germination behaviour for this species has never been systematically analysed. ForPaspalumspp., dry‐storage and moist cold or warm pre‐conditioning treatments have been reported as effective for the relief or breaking of seed dormancy. In the present work, seed germination responses at 32°C were assayed for sixteenP. dilatatumgenotypes, representing its known natural genetic variability, to two moist pre‐conditioning treatments (at 5 and 20°C) and without pre‐conditioning, and three seed storage periods (0, 3 and 6 months). Pre‐conditioning at 20°C showed high germination percentages (&gt;80%), with ratios equal to or higher than pre‐conditioning at 5°C, suggesting that cold is not required to break dormancy. Longer storage times resulted in increases in germination responses for most of the genotypes, while other biotypes showed no effect. BiotypesVirasoro andChirú showed a remarkably different behaviour with higher germination percentages of untreated freshly harvested seeds. Our results show that diversity for traits involved in seed germination exists among naturally occurringP. dilatatumgenotypes and the characterization of these traits should be addressed during ecotype characterization and evaluation of potential domesticates of this species.

Selection of crop cultivars suited to the location combined with astute management can reduce crop yield penalties in pasture cropping systems

Pasture cropping is an emerging farming-systems practice of southern Australia, in which winter grain crops are sown into an established stand of a winter-dormant, summer-growing perennial pasture. There is a pressing need to define times, locations and climates that are suitable for pasture cropping. To evaluate effects of management interventions, agro-environment, and possible interactions on crop and pasture productivity associated with pasture cropping, an AusFarm® simulation model was built to describe a pasture-cropping system based on annual crop and subtropical grass. The model was parameterised using data from field research on pasture cropping with barley cv. Buloke and a C4 subtropical grass, Gatton panic (Panicum maximum cv. Gatton), conducted at Moora, Western Australia. The simulation was run over 50 years using the historical climate data of five southern Australian locations (Cunderdin, Jerdacuttup, Mingenew, and Moora in Western Australia, and Karoonda in South Australia). Two wheat cultivars and one barley crop were considered for each location, to examine the impact of crop phenology on this farming system. Jerdacuttup and Moora favoured pasture cropping, with average barley-yield penalties of 10 and 12%. These locations were characterised by colder growing seasons, more plant-available water at anthesis, and more winter–spring rain. The cereal crops did not rely on stored soil moisture, growing instead on incident rain. The winter–spring growth of the Gatton panic pasture was highest at Mingenew. This generated a high yield penalty, 38% loss under pasture cropping, compared with the other locations. Changing the efficacy of a herbicide application to the pasture when the crop was sown had a strong effect on yield. Yield penalties at Moora and Mingenew reduced to 7 and 29%, respectively, when the proportion of live biomass killed by the herbicide was doubled. Utilisation of soil moisture by the Gatton panic pasture during summer and early autumn had little effect on subsequent grain yield, whereas reduced pasture growth during the winter–spring growing period had a substantial effect on crop yield. Pasture cropping can therefore succeed in agro-climatic regions where crops can be grown on incident rain and pasture growth is suppressed through low temperature or herbicide. Perennial pasture growth should be minimised during the crop growing period through the management of crop sowing date, nitrogen fertiliser application and C4 grass suppression to minimise the effect on stored soil water at crop anthesis.

Pasture cropping with C4 grasses in a barley–lupin rotation can increase production

In southern Australia, intercropping, pasture cropping and overcropping have evolved as techniques to address environmental problems such as dryland salinity and wind erosion and to utilise soil water outside the conventional winter-dominant growing season. We paired three winter-dormant pastures, including two subtropical C4 perennial species (Rhodes grass, Chloris gayana; Gatton panic, Megathyrsus maximus) and the summer-active perennial C3 legume siratro (Macroptilium atropurpureum), with a conventional barley (Hordeum vulgare)–lupin (Lupinus angustifolius) rotation to explore the extent to which different summer-active species reduced crop yields. We also examined whether the competition for resources could be altered by supplying increased nitrogen to the crop and changing the row spacing of the pasture. Under high-input conditions, pasture reduced cereal crop yields by up to 26% and lupin yields by up to 29%. Under low-input conditions, pasture cropping did not significantly reduce crop yield, and frequently increased crop yields. With low inputs, barley yield increases in 2011 ranged from 23% to 31%. In lupins under low-input conditions, yield increases ranged from 91% to 106% in 2010 and from –6% to +39% in 2012. The impact of the crop on the pasture was less pronounced, where the timing of pasture growth was delayed by the crop, but absolute levels of production were not influenced by the crop. Row spacing altered the temporal dynamic of pasture production; initially, the pasture produced less than the narrow spaced equivalent, but after 2 years, production exceeded that in the narrow row. Across all pasture species in 2009 and 2012, winter pasture production reduced crop yield by 0.32 and 0.4 t grain/ha pasture biomass produced, implying that moderate yield losses occurred because pasture production was also moderate. In the other two years, winter pasture production did not affect crop yield, suggesting that the pasture was able to utilise resources surplus to crop requirements. In this environment, with this combination of crops and summer-active pastures, higher levels of inputs did not enhance crop yield in a pasture-cropping system. We suggest that grain yield losses are lower in the low-input system and this implies that, at some level, competition between the species was reduced in a nitrogen-limited environment and the extent of the competition depended on season.

Italian Ryegrass (Lolium perenne ssp. multiflorum) and Corn (Zea mays) Competition

Italian ryegrass is an annual/biennial grass that is typically used as a pasture crop or a cover crop along roadsides, rights-of-way, and industrial areas. Glyphosate-resistant (GR) Italian ryegrass populations have been documented around the world, mostly in orchard and vineyard situations. The first evidence of evolved GR Italian ryegrass in row/agronomic crops was reported from Washington County, Mississippi in 2005. GR Italian ryegrass populations can jeopardize preplant burndown options in reduced-tillage crop production systems, thereby, delaying planting operations. The effects of competition of Italian ryegrass on crop growth and yield are poorly understood. A field study was conducted in the 2012 growing season and repeated in the 2013 growing season. GR and susceptible (GS) Italian ryegrass populations were established in the greenhouse and transplanted in prepared corn row beds in the fall of 2011 and 2012 at 0, 1, 2, 3, and 4 plants·meter> of crop row. Italian ryegrass plants overwintered and developed over the following spring-summer. Glyphosate was applied at 1.26 kg·ae/ha (1.5× of labeled rate) in the spring to burndown the Italian ryegrass plants and corn was planted into the ryegrass residue 2 - 3 wk later. Current corn production practices were followed. Corn density (early and late season), height (early season), and yield and Italian ryegrass biomass (early-mid season) measurements were recorded during both years. Corn height was greater in 2012 than that in 2013 at comparable stages of the growing season, due to a cooler and wetter early season in 2013 than that in 2012. Averaged across weed densities, corn density (both early and late season) and yield were higher in the GS than those in the GR population, but Italian ryegrass biomass was similar for both populations. Averaged across Italian ryegrass populations, corn density (both early and late season), and yield were inversely proportional to Italian ryegrass density. In summary, Italian ryegrass significantly reduced corn density and yield and reduction was greater with the GR than that with the GS population. Studies are underway to study inter population competition in Italian ryegrass and investigate allelopathic effects of Italian ryegrass on selected crops.

Soil organic carbon mineralization rates in aggregates under contrasting land uses

Measuring soil organic carbon (SOC) mineralization in macro-aggregates (250–2000μm), micro-aggregates (250–53μm) and the <53μm fraction helps to understand how spatial separation of SOC inside soil aggregates regulates its dynamics. We hypothesized that (i) compared with macro-aggregates SOC mineralization rate of micro-aggregates would be slower, (ii) adsorption of SOC on <53μm fraction decreases the SOC mineralization rate, and (iii) land use has a significant influence on SOC decomposition rate. To test these hypotheses we collected topsoil from Dermosol (Acrisols in FAO Soil Classification) sites under three contrasting land uses namely native pasture (NP), crop–pasture rotation (CP) and woodland (WL). Macro-aggregates, micro-aggregates and the <53μm fraction were separated from bulk soil by wet sieving. The three aggregate size ranges were then incubated for six months and CO2 evolution was measured at different time intervals. The chemically stable SOC of <53μm fraction of macro-aggregates, micro-aggregates and the <53μm fraction (separated by wet sieving) was measured by oxidation of SOC with 10% H2O2. On average, cumulative mineralization, Cmin (gCO2–Ckg−1 aggregate) of the <53μm fraction, was 28% lower than that of macro-aggregates and micro-aggregates. However, SOC mineralized (SOCmin) was similar in all size fractions. The size of slow SOC pool (percent of SOC concentration in aggregates) was also significantly higher in the <53μm fraction and ranged from 58 to 96%, across aggregate sizes. However, the chemically stable SOC (percent of SOC concentration in aggregates) was significantly higher in macro-aggregates and micro-aggregates than that of the <53μm fraction. Mean residence time (MRT) of slow SOC pool (MRTs) was higher in the <53μm fraction than for either macro-aggregates or micro-aggregates. Among the land uses NP had higher SOCmin compared with CP and WL. In conclusion, the insignificant difference in SOCmin, slow SOC pool sizes and MRTs between macro-aggregates and micro-aggregates indicated that SOC mineralization rate and thus the protection of SOC was similar in both macro-aggregates and micro-aggregates.

Agronomic and environmental impacts of pasture–crop rotations in temperate North and South America

Agriculture has become increasingly specialized in response to political, regulatory, sociological, and economic pressures to meet market demands of an ever-larger food and fiber processing sector. However, there is a growing concern with specialized agricultural systems, because of increasingly negative responses on the environment from declining soil quality to eutrophication of water bodies and enhanced greenhouse gas emissions. Literature from North and South America was reviewed that showed (i) strong positive production outcomes of crops grown following pastures, (ii) enhancement of soil organic matter with perennial pastures, particularly in the surface soil, (iii) improvement in water infiltration and water quality, and (iv) synergies between crop and livestock systems in system-wide evaluations of production and environmental quality. Therefore, agricultural soils would benefit from the re-introduction of perennial grasses and legumes into the landscape (i.e. temporally and/or spatially) by regaining soil organic matter and strengthening their capacity for long-term productivity and environmental resiliency.

Remote Sensing for sustainable agriculture

Worldwide agricultural production encompasses 3500 million ha of pasture and fodder crops and 1559 million ha of cultivated lands, of which 28% is prime land, 52% is good land, and 20% is marginal ...

Qualidade da água em microbacias hidrográficas com diferentes coberturas do solo no sul do Espírito Santo

O objetivo deste trabalho foi avaliar a qualidade das águas superficiais e subterrâneas em microbacias hidrográficas caracterizadas por diferentes coberturas do solo: pastagem, floresta e cafeeiro. Foi desenvolvido um índice de qualidade de água utilizando a análise de componentes principais, que proporcionou a redução das 13 características de qualidade em duas componentes, que explicaram 91,2% da variância total. As águas superficiais e subterrâneas das microbacias foram adequadas ao consumo humano, após tratamento convencional, ao longo de todo o período estudado, exceto a água subterrânea da microbacia coberta com pastagem no período de estiagem.

Land use intensity and cropping sequence effects on aggregate stability and C storage in a Vertisol and a Mollisol

The relevant change in land use due mainly to the rapid expansion of soybean cropping towards areas traditionally occupied for livestock purposes or with native grasslands of South America may have negative consequences on soil organic carbon (SOC) storage and aggregate stability, although the effect may be different between soils with contrasting aggregation agents. The aim of our work was to assess the impact of the land use, measured as the intensification and/or frequency of a given crop, on SOC storage and aggregate stability in two soils differing in their main agents of aggregation. The study was conducted in a Mollisol and a Vertisol of Argentina. Eleven cropped fields (agricultural and crop–pasture rotation) under no-tillage and one uncropped situation (pristine native grassland) were selected in each soil type. The fraction of annual time with plant cover (as a measure of the intensification in the land use) and the frequency of a given crop in the cropping sequence over a 6-year period were calculated. Undisturbed soil samples were collected from each soil at 0–5, 5–15 and 15–30cm depths. The SOC stocks in equivalent soil mass were calculated using the native grassland as the baseline system. Aggregate stability was evaluated using a method that involved three pretreatments: fast wetting, stirring after prewetting and slow wetting. The intensification improved the aggregate stability in the Mollisol, whereas a low impact of land use on aggregate stability was recorded in the Vertisol. Overall, both the intensification sequence index and the soybean cropping frequency were the best indexes to evaluate the impact of land use on aggregate stability and SOC storage, mainly in the Mollisol. The stirring after prewetting pretreatment was mainly associated with SOC concentration in the Mollisol, appearing as a method with high potential capacity to discriminate land use in the Mollisol, in which the SOC is the main aggregation agent. In contrast, the slow wetting pretreatment was more appropriate to evaluate the impact of land use in the Vertisol. The approach used to evaluate the land use, which included agricultural lands, crop–pasture rotation and native grasslands, evaluated through indexes of occupation with plant cover, was more suitable for the Mollisol than for the Vertisol. This reveals that the evaluation of land use through several indexes should be based on the soil type.

Combining management based indices with environmental parameters to explain regional variation in soil carbon under dryland cropping in South Australia

Identifying drivers of variation in soil organic carbon (OC) at a regional scale is often hampered by a lack of historical management information. Focusing on red-brown-earth soils (Chromosol) under dryland agriculture in the Mid-North and Eyre Peninsula of South Australia, our aims were 2-fold: (i) to provide a baseline of soil OC stocks (0.3 m) and OC fractions (mid-infrared predictions of particulate, humus, and resistant OC in 0.1 m samples) in cropping and crop-pasture systems; and (ii) to evaluate whether the inclusion of management-based indices could assist in explaining regional-level variation in OC stocks and fractions. Soil OC stocks in both regions varied ~20 Mg ha–1, with higher OC stocks in the Mid-North (38 Mg ha–1) than the Eyre Peninsula (29.1 Mg ha–1). The humus OC fraction was the dominant fraction, while the particulate OC was the most variable. Environmental variables only partially explained soil OC variability, with vapour pressure deficit (VPD) offering the greatest potential and likely acting as an integrator of temperature and moisture on plant growth and decomposition processes. Differences between broad-scale cropping and crop–pasture systems were limited. In the Mid-North, variability in soil OC stocks and fractions was high, and could not be explained by environmental or management variables. Higher soil OC concentrations (0.1 m) in the Eyre Peninsula cropping than crop–pasture soils were largely accounted for in the particulate OC fraction and are therefore unlikely to represent a long-term stable OC pool. Use of the management data in index format added some explanatory power to the variability in OC stocks over the main environmental variables (VPD, slope) within the Eyre Peninsula cropping soils only. In the wider context, the management data were useful in interpreting differences between regional findings and highlighted difficulties in using uninformed, broad-scale management categories.

Potential for biological nitrification inhibition to reduce nitrification and N2O emissions in pasture crop–livestock systems

Agriculture and livestock production systems are two major emitters of greenhouse gases. Methane with a GWP (global warming potential) of 21, and nitrous oxide (N2O) with a GWP of 300, are largely emitted from animal production agriculture, where livestock production is based on pasture and feed grains. The principal biological processes involved in N2O emissions are nitrification and denitrification. Biological nitrification inhibition (BNI) is the natural ability of certain plant species to release nitrification inhibitors from their roots that suppress nitrifier activity, thus reducing soil nitrification and N2O emission. Recent methodological developments (e.g. bioluminescence assay to detect BNIs in plant root systems) have led to significant advances in our ability to quantify and characterize the BNI function. Synthesis and release of BNIs from plants is a highly regulated process triggered by the presence of NH4+ in the rhizosphere, which results in the inhibitor being released precisely where the majority of the soil-nitrifier population resides. Among the tropical pasture grasses, the BNI function is strongest (i.e. BNI capacity) in Brachiaria sp. Some feed-grain crops such as sorghum also have significant BNI capacity present in their root systems. The chemical identity of some of these BNIs has now been established, and their mode of inhibitory action on Nitrosomonas has been characterized. The ability of the BNI function in Brachiaria pastures to suppress N2O emissions and soil nitrification potential has been demonstrated; however, its potential role in controlling N2O emissions in agro-pastoral systems is under investigation. Here we present the current status of our understanding on how the BNI functions in Brachiaria pastures and feed-grain crops such as sorghum can be exploited both genetically and, from a production system's perspective, to develop low-nitrifying and low N2O-emitting production systems that would be economically profitable and ecologically sustainable.

Condição estrutural de um argissolo no Rio Grande do Sul, em floresta nativa, em pastagem cultivada e em povoamento com eucalipto

http://dx.doi.org/10.5902/198050987564Objetivou-se definir limites críticos dos atributos físico-hídricos em áreas sob floresta e pastagem e avaliar a intensidade de compactação desses usos em um Argissolo Vermelho distrófico no Sul do Brasil. Os usos do solo constituíram-se de: Floresta - composta por espécies arbóreas e arbustivas; Pastagem - com cinco anos de idade, constituída de braquiária brizanta (Brachiaria brizantha) consorciada com pensacola (Paspalum lourai) e trevo (Trifolium sp.); Eucalipto 20 - povoamento de Eucalyptus saligna com vinte anos de idade, sendo realizado o preparo convencional do solo para implantação do povoamento; Eucalipto 4,5 - plantio clonal de Eucalyptus saligna conduzido em 2a rotação, com 4,5 anos de idade. Foram avaliadas a condutividade hidráulica do solo saturado, a porosidade (macro, micro e total) e a densidade do solo. O eucalipto tem potencial para ser utilizado em áreas de recuperação, sem objetivo comercial. A compactação aumenta a densidade e diminui a macroporosidade e porosidade total do solo até a camada de 0,40 m em eucalipto com fins comerciais e até a camada de 0,10 m em pastagem. Valores baseados em restrições ao crescimento e rendimento de culturas anuais ou no intervalo hídrico ótimo têm potencial para serem utilizados para culturas perenes e pastagem.

Early Season Host Plants of &lt;I&gt;Apolygus lucorum&lt;/I&gt; (Heteroptera: Miridae) in Northern China

Apolygus lucorum (Meyer-Dür) (Heteroptera: Miridae) has become a severe pest of cotton and many other crops in northern China as a result of the widespread adoption of Bacillus thuringiensis (Berliner) cotton, with a corresponding reduction of broad-spectrum insecticide application in cotton fields. From the middle of April to middle June, A. lucorum feeds and develops on other host plants before dispersing to cotton fields. Effective suppression of A. lucorum populations before they enter cotton fields may be an excellent strategy for reducing the occurrence and damage of their subsequent generations in cotton fields. For that, basic information about the host plant range of A. lucorum during the early season is needed. Between 2006 and 2010, a total of 94 plant species from 41 families covering 39,956 square meters of land in natural conditions were sampled using the standard white pan beat method. Sixty-six plant species, including 45 weeds, 10 fruit trees, 5 timber trees, 4 pasture crops, and 2 arable crops were found to be hosts of A. lucorum. Among these species, Descurainia sophia (L.) Webb ex Prantl, Humulus scandens (Loureiro) Merrill, Zizyphus jujuba Miller, Vitis vinifera L., Viciafaba L., and Medicago sativa L. were identified as dominant host species because of their wide distribution and high population densities of A. lucorum. The results of this study provide useful information about the early season host range of A. lucorum, which can be used to develop effective strategies to control the pest before its dispersal to cotton fields.