Farm-scale Study Research Articles

Optimising POXC effective sensitivity as a soil indicator in Australian soils

The continuum of soil organic carbon is currently not well represented by any single metric. Permanganate oxidizable carbon (POXC) has been widely utilized as a soil condition indicator due to its correlation with biological indicators and sensitivity to management effects over relatively short time periods. However, the ability of POXC to represent the continuum of soil organic carbon, and how this could improve the characterization of management effects, has not been sufficiently explored. This study investigated the relationship between permanganate concentration and POXC across nine permanganate concentrations ranging from 3 to 300 mM. An initial investigation was performed on ten cropped and uncropped topsoil pairs representing a diverse range of soil types across New South Wales, Australia, and an additional 52 sites were investigated in a farm-scale study. POXC was observed to increase monotonically and non-linearly with increasing permanganate concentration. POXC characteristics were developed by fitting a logistic function to the observed data, which facilitated calculation of the area under the curve (POXCAUC) and the theoretical maximum POXC (POXCmax). The utility of the POXC characteristic was demonstrated with highly significant differences (p ≤ 0.002) observed in POXCAUC between cropped and uncropped sites. POXCAUC also displayed larger probability test statistics compared to any single permanganate concentration. The investigation also revealed that if a single concentration were to be utilized for australian soils, the 50 mM concentration was more effective at discerning land use effects in clayey (p = 0.000) and sandy (p = 0.049) sites compared to the widely adopted 20 mM concentration (p = 0.001; p = 0.312).

Predicting Long-Term Effects of Alternative Management Practices in Conventional and Organic Agricultural Systems on Soil Carbon Stocks Using the DayCent Model

Recently, many countries have introduced policies that promote sustainable agricultural practices, such as reducing synthetic nitrogen fertiliser and promoting diversified crop rotation. While such management changes might represent an opportunity for the agricultural sector to mitigate the impacts of climate change through carbon (C) sequestration in soils, there are still uncertainties due to the scarcity of reliable long-term data to prove this assumption. In this study, we applied the DayCent model using empirical data from a farm-scale study and an experimental trial study at Nafferton farm in the UK, to assess the long-term effects of contrasting agricultural systems (conventional vs. organic), grazing regimes (non-grazed vs. grazed), arable systems with ley phases, mineral vs. compost fertility sources and conventional vs. organic crop rotation on soil C stocks (0–0.20 m depth). The simulations showed that grazing and higher ley time proportions can increase soil C stocks for a period of at least 30 years, regardless of the agricultural system used (average increase in rates of 0.25 ± 0.02 Mg ha−1 yr−1). Compost fertiliser promoted soil C accumulation for the same period (average increase in rates of 0.3 Mg ha−1 yr−1), but its magnitude was dependent on the choice of crops in the rotation. However, ley time proportions higher than 40% of the full crop rotation did not improve soil C accumulation further. We conclude that the DayCent model can be used to identify the quantity of and the effective period for which management practices can be used to target mitigation efforts, but the balance between sustainability and productivity aspects warrants further research.

Effects of Cashew Nut Shell Liquid on Hindgut Fermentation and Microbiota of Chickens

Cashew nut shell liquid (CNSL), a feed additive for chickens, was evaluated for its influence on the hindgut environment by determining fermentation and bacterial profiles using cecal contents, fecal slurry and pure cultures. A farm-scale study showed that CNSL feeding to broiler chickens from 0 to 42 days of age improved body weight gain and lowered mortality. Cecal levels of short chain fatty acids increased with CNSL feeding, while ammonia and indole levels decreased. Feeding CNSL decreased the relative abundance of cecal bacteria belonging to some clostridial groups and Ruminococcaceae. In particular, Clostridium perfringens was undetectable following CNSL feeding. A pure culture study showed that CNSL (≥ 6.25 μg/ml) inhibited C. perfringens growth, accompanied by cell surface disruption based on electron microscopic observation. Fermentation profiles of slurry cultures prepared from feces of chickens were altered by CNSL supplementation toward less ammonia production. The lowered ammonia was correlated positively with the abundance of unclassified Lachnospiraceae and unclassified Ruminococcaceae, and negatively with unclassified Enterobacteriaceae and Sutterella. These results suggest that CNSL could exert its beneficial influence on the hindgut health of chickens through impacting the microbiota.

Investigating soybean (Glycine max L.) responses to irrigation on a large-scale farm in the humid climate of the Mississippi Delta region

The shallow Lower Mississippi River Valley Alluvial Aquifer, which supports irrigated agriculture in the Lower Mississippi Delta (LMD) region, is fast depleting from unsustainable water extractions for irrigations. The survival of irrigated agriculture in the region today hinges on enhancing the irrigation use efficiencies of the water pumped out. Furrow irrigation practices (surface or flood irrigation) dominate the LMD region's irrigated agriculture scenario. We investigated soybean productivity in response to irrigations applied through every furrow (FI), applied through alternate furrow (AFI), and rainfed (RF, no irrigation). Approximately half the volume of water applied in FI was applied in the AFI. The experiments were conducted in 2016, 2018, and 2020, which constituted the soybean phases of a corn-soybean rotation trial conducted on a clay soil in farm-scale plots (15 ha). The plots were equipped with eddy covariance systems for quantifying crop water use (ET, evapotranspiration). There was no appreciable difference in soybean grain yield between FI and AFI, but RF yielded significantly lower than FI and AFI. Leaf area index was also significantly lower in RF compared to FI and AFI. Across the three years, the average reduction in soybean yield was only 2% in AFI, while it was 24% in RF compared to FI. Average grain yields were 4507, 4413, and 3422 kg ha−1; seasonal ET were 549, 562, and 527 mm; and water use efficiencies (WUE) were 8, 8, and 7 kg ha−1 mm−1 in FI, AFI, and RF, respectively. This large farm-scale study demonstrated that grain yields from irrigating soybean through alternate furrows were comparable to irrigating through every furrow, thus saving about half the water pumped out of the aquifer. This unique study was conducted in farm-scale fields; as such, the results obtained directly apply to a farm environment, so they are ready for recommendation to soybean farmers for adoption without further field trials.

Soil nutrient availability and microclimate are influenced more by genotype than by planting stock type in hybrid poplar bioenergy buffers on farmland

Bioenergy buffers planted with fast-growing woody crops such as hybrid poplars (Populus spp.) are increasingly integrated into agricultural land to enhance the provision of ecosystem services. Genotype and planting stock type selection may influence buffer establishment success and soil properties, which may affect buffer functions such as soil nutrient removal, hydrological regulation (i.e. soil dewatering) or local climate regulation (i.e. temperature reduction). This farm-scale study tested the effects of two unrelated hybrid poplar genotypes (P. deltoides × P. nigra, genotype D × N-3570 and P. maximowiczii × P. balsamifera, genotype M × B-915311) and two planting stock types (unrooted whips and bare-root stocks) on biomass growth, soil nutrient availability and soil microclimate in 15 m wide bioenergy buffers located downslope of hayfields in the cold temperate region of southern Québec, Canada. Poplar genotype had an important effect on biomass growth, soil microclimate and the supply rates of several macronutrients and micronutrients, while planting stock type had little effect on these variables. The P. maximowiczii × P. balsamifera genotype produced the highest biomass and had generally lower nutrient availability in the soil, but not for soil NO3, which was less available under the P. deltoides × P. nigra genotype. Compared to the hayfield soils, only the P. maximowiczii × P. balsamifera genotype maintained a lower supply rate of available P in the buffer soil. Compared to the hayfield soils, NH4 supply rates were lower in the buffers for both genotypes, while NO3 supply rates were similar or higher. Both genotypes had the capacity to maintain cooler soil temperatures and lower moisture content in the soil of the buffer compared to the adjacent hayfields, but this capacity was greater for the P. maximowiczii × P. balsamifera genotype. Because plant-soil interactions are strongly affected by hybrid poplar genetics, genotype selection is an important consideration in the design of multifunctional agricultural buffers. In temperate agroecosystems, future studies should try to identify productive poplar genotypes that would decrease topsoil NO3 and P availability and reduce soil water content in order to minimize potential N and P losses from buffer soils during runoff events.

Impact assessment of Bt maize expressing the Cry1Ab and Cry2Ab protein simultaneously on non-target arthropods.

Transgenic maize expressing the Cry1Ab and Cry2Ab protein simultaneously from Bacillus thuringiensis (Bt-maize) has been grown for farm-scale study to investigate its potential impact to non-target arthropod (NTA). The trials were conducted between Bt maize 2A-7 and its parental line (B73-329) in Beijing, China, over 3years. Richness (C), Shannon index (H), Pielou index (J), Simpson index (D), and Bray-Curtis index were used to evaluate the population dynamics and biodiversity of the dominant arthropods from per 50 plants in crop field. The mainly abundant groups were Aphidoidea, Araneae, Coccinellidae, Anthocoridae, and Thripidae which represented about 90% of the total number of NTA. Although the abundance of NTA varied from year to year, there is no significant difference between Bt maize and non-Bt maize field. Fluctuations were found at individual sample dates, but the trend of these descriptors remained consistent. Further analysis showed the biodiversity indexes of the dominant arthropods C, H, J, D, and Bray-Curtis dissimilarity between Bt maize producing Cry1Ab and Cry2Ab toxin simultaneously and its parental line had no significant difference except for some sampling dates. These results suggested that Bt maize is compatible with the NTAs and provides further evidence of the ecological impact of genetically modified maize.

Strategic Grazing in Beef-Pastures for Improved Soil Health and Reduced Runoff-Nitrate-A Step towards Sustainability

Generally, improvement in the soil health of pasturelands can result in amplified ecosystem services which can help improve the overall sustainability of the system. The extent to which specific best management practices have this effect has yet to be established. A farm-scale study was conducted in eight beef-pastures in the Southern Piedmont of Georgia, from 2015 to 2018, to assess the effect of strategic-grazing (STR) and continuous-grazing hay distribution (CHD) on soil health indicators and runoff nitrate losses. In 2016, four pastures were converted to the STR system and four were grazed using the CHD system. Post-treatment, in 2018, the STR system had significantly greater POXC (by 87.1, 63.4, and 55.6 mg ha−1 at 0–5, 5–10, and 10–20 cm, respectively) as compared to CHD system. Soil respiration was also greater in the STR system (by 235 mg CO2 m-2 24 h−1) and less nitrate was lost in the runoff (by 0.21 kg ha−1) as compared to the CHD system. Cattle exclusion and overseeding vulnerable areas of pastures in STR pastures facilitated nitrogen mineralization and uptake. Our results showed that the STR grazing system could improve the sustainability of grazing systems by storing more labile carbon, efficiently mineralizing soil nitrogen, and lowering runoff nitrate losses.

Spatial and Temporal Genetic Diversity of the Peach Potato Aphid Myzus persicae (Sulzer) in Tunisia.

The peach potato aphid, Myzus persicae (Sulzer), is a worldwide pest of many crops, and the most important aphid pest of peach and potato crops in Tunisia, mainly due to virus transmission, for which insecticides are frequently applied. We studied the genetic structure of M. persicae populations in Tunisia, in order to further our understanding of the biotic and abiotic factors shaping populations and to predict their evolutionary responses to the present management practices. We monitored peach orchards and seed potato crops in different seasons and regions from 2011–2013 and in 2016 (19 populations), assessing the genetic diversity of M. persicae at six microsatellite loci. Temporal and spatial changes in the frequency and distribution of 397 genotypes in 548 sampled aphids were studied. Only 37 genotypes were found more than once (clonal amplification), as most genotypes were found only once (91.60% in peach; 88.73% in potato crops). A similarly high genetic diversity was observed in aphids sampled from peach (G/N = 0.76; Ho = 0.617) and potato (G/N = 0.70; Ho = 0.641). Only a weak genetic differentiation among populations was found, mainly between geographic locations. Clustering analysis revealed genotypes to be grouped mainly according to host plant. The availability of the primary host, high proportion of unique genotypes, high genetic diversity and lack of structuring suggest that the aphid reproduces mainly through cyclical parthenogenesis in Tunisia. On the other hand, we provide a farm-scale study that shows how easily M. persicae can colonize different areas and hosts, which may have important implications in relation to plant virus vectoring.

Intermittent agitation of liquid manure: effects on methane, microbial activity, and temperature in a farm-scale study

ABSTRACTLiquid manure storages are a significant source of methane (CH4) emissions. Farmers commonly agitate (stir) liquid manure prior to field application to homogenize nutrients and solids. During agitation, manure undergoes mechanical stress and is exposed to the air, disrupting anaerobic conditions. This on-farm study aimed to better understand the effects of agitation on CH4 emissions, and explore the potential for intentional agitation (three times) to disrupt the exponential increase of CH4 emissions in spring and summer. Results showed that agitation substantially increased manure temperature in the study year compared to the previous year, particularly at upper- and mid-depths of the stored manure. The temporal pattern of CH4 emissions was altered by reduced emissions over the subsequent week, followed by an increase during the second week. Microbial analysis indicated that the activity of archaea and methanogens increased after each agitation event, but there was little change in the populations of methanogens, archaea, and bacteria. Overall, CH4 emissions were higher than any of the previous three years, likely due to warmer manure temperatures that were higher than the previous years (despite similar air temperatures). Therefore, intermittent manure agitation with the frequency, duration, and intensity used in this study is not recommended as a CH4 emission mitigation practice.Implications: The potential to mitigate methane emissions from liquid manure storages by strategically timed agitation was evaluated in a detailed farm-scale study. Agitation was conducted with readily-available farm equipment, and targeted at the early summer to disrupt methanogenic communities when CH4 emissions increase exponentially. Methane emissions were reduced for about one week after agitation. However, agitation led to increased manure temperature, and was associated with increased activity of methanogens. Overall, agitation was associated with similar or higher methane emissions. Therefore, agitation is not recommended as a mitigation strategy.

Weeds and ground-dwelling predators' response to two different weed management systems in glyphosate-tolerant cotton: A farm-scale study.

The use of glyphosate, as a post-emergence broad-spectrum herbicide in genetically modified glyphosate-tolerant (GT) cotton, supposes a big change in weed management programs with respect to a conventional regime. Thus, alterations in arable flora and arthropod fauna must be considered when evaluating their potential impacts. A 3-year farm-scale study was conducted in a 2-ha GT cotton crop, in southern Spain, to compare the effects of conventional and glyphosate herbicide regimes on weed abundance and diversity and their consequences for ground-dwelling predators. Surveys reveal that weed density was relatively low within all treatments with a few dominant species, with significantly higher weed densities and modifications of the floristic composition in glyphosate-treated plots that led to an increase in the abundance of Portulaca oleracea and to a reduction in plant diversity. The activity-density of the main predatory arthropod taxa (spiders, ground beetles, rove beetles and earwigs) varied among years, but no significant differences were obtained between conventional and glyphosate herbicide regimes. However, significant differences between treatments were obtained for ground beetles species richness and diversity, being higher under the glyphosate herbicide regime, and a positive correlation with weed density could be established for both parameters. The implications of these findings to weed control in GT cotton are discussed.

Riparian buffer growth and soil nitrate supply are affected by tree species selection and black plastic mulching

Tree species selection in the design of agricultural riparian buffers is important to optimize particular ecosystem services, while vegetation management (weed treatment) is often critical in obtaining first-rate tree growth and survival. This farm-scale study took place along a 1km section of a headwater stream in southern Québec (southeastern Canada). Five tree species with contrasted ecological characteristics were planted (Populus×canadensis, Fraxinus pennsylvanica, Quercus macrocarpa, Quercus rubra and Pinus strobus), with black plastic (polyethylene) mulches as the vegetation management method, as well as a control with no vegetation management, all within a fenced herbaceous riparian buffer. Tree growth and survival were measured along with soil nutrient supply. Significant Species×Vegetation treatment interactions where observed for all growth variables (p<0.001), but also for soil nitrate (NO3) supply (p<0.01). All species benefited from the plastic mulch treatment, but varied greatly in their responses. After 5 years, mulched hybrid poplar produced 774 times more stem volume than red oak without mulch. Across all species/vegetation treatment combinations, a 13-fold variation in soil NO3 supply rate was observed during the 4th growing season. Compared to the other species, NO3 supply rate in hybrid poplar plots was 39–87% lower in the plastic mulch treatment and 48–62% lower in the control treatment. Significantly higher soil NO3 supply rates were observed beneath the mulches of non nitrophilous species (white pine and red oak). Red oak growth was negatively correlated with NO3 supply (R2=0.57, p<0.05) in the mulch treatment. Early-successional nitrophilous species (hybrid poplar and red ash) planted with the plastic mulch led to the lowest increase in soil NO3 and the greatest gains in buffer structural attributes (stem volume, diameter and height). Hybrid poplar growth was positively correlated with soil NO3 supply (R2=0.86, p<0.001) in the control treatment. Natural abandoned field/grassland invaders (white pine and bur oak) grew well without black plastic mulch, while the growth of non-mulched red oaks was marginal. In the control treatment, stem volume was a strong negative predictor (across all species) of soil NO3 supply (R2=0.91, p<0.05), indicating that under herbaceous vegetation competition larger trees have a greater ability to reduce soil NO3. This study provides evidence that particular tree species/vegetation management treatment combinations strongly influence early riparian buffer structural development and soil NO3 dynamics in agricultural riparian zones.

Farm-scale evaluation of the impact of Cry1Ab Bt maize on canopy nontarget arthropods: a 3-year study.

The cultivation of Cry1Ab-expressing genetically modified MON810 (Bt maize) has led to public concern in Europe, regarding its impact on nontarget arthropods (NTAs). We have assessed the potential effects of DKC 6451 YG (MON810) maize on canopy NTAs in a farm-scale study performed in Central Spain during 3 years. The study focused on hemipteran herbivores (leafhoppers and planthoppers) and hymenopteran parasitic wasps (mymarids) collected by yellow sticky traps, which accounted for 72% of the total number of insects studied. The dynamics and abundance of these groups varied among years, but no significant differences were found between Bt and non-Bt maize, indicating that Bt maize had no negative effect on these taxa. Nonetheless, the Cry1Ab toxin was detected in 2 different arthropods collected from Bt maize foliage, the cicadellids Zyginidia scutellaris and Empoasca spp. A retrospective power analysis on the arthropod abundance data for our field trials has determined that Z. scutellaris and the family Mymaridae have high capacity to detect differences between the Bt maize and its isogenic counterpart. The use of these canopy NTAs as surrogates for assessing environmental impacts of Bt maize is discussed.

Genetic diversity and insecticide resistance during the growing season in the green peach aphid (Hemiptera: Aphididae) on primary and secondary hosts: a farm-scale study in Central Chile

The seasonal dynamics of neutral genetic diversity and the insecticide resistance mechanisms of insect pests at the farm scale are still poorly documented. Here this was addressed in the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) in Central Chile. Samples were collected from an insecticide sprayed peach (Prunus persica L.) orchard (primary host), and a sweet-pepper (Capsicum annum var. grossum L.) field (secondary host). In addition, aphids from weeds (secondary hosts) growing among these crops were also sampled. Many unique multilocus genotypes were found on peach trees, while secondary hosts were colonized mostly by the six most common genotypes, which were predominantly sensitive to insecticides. In both fields, a small but significant genetic differentiation was found between aphids on the crops vs. their weeds. Within-season comparisons showed genetic differentiation between early and late season samples from peach, as well as for weeds in the peach orchard. The knock-down resistance (kdr) mutation was detected mostly in the heterozygote state, often associated with modified acetylcholinesterase throughout the season for both crops. This mutation was found in high frequency, mainly in the peach orchard. The super-kdr mutation was found in very low frequencies in both crops. This study provides farm-scale evidence that the aphid M. persicae can be composed of slightly different genetic groups between contiguous populations of primary and secondary hosts exhibiting different dynamics of insecticide resistance through the growing season.

A Farm-Scale Test of Nitrogen Assimilation by Vegetated Buffer Systems Receiving Swine Lagoon Effluent by Overland Flow

A farm-scale study was conducted from 2000 to 2004 to determine the effectiveness of grass-forest vegetated buffers in assimilating nitrogen (N) from overland flow application of swine lagoon effluent. The rationale for the study was that replicated buffer plot studies had shown that vegetated buffers will effectively assimilate N, but it was not known whether or not they would work at a larger scale. The study was conducted on a commercial farm near Tifton, Georgia. Wastewater was pumped from a single-stage anaerobic lagoon to vegetated buffers composed of grass and mature or newly planted pines. The buffers approximated 60 m in length by 90 m in width. The upper 10 m of each buffer was in grass, while the downslope area was in mature or newly planted pines. Six buffers were instrumented for wastewater application and water quality monitoring. Two buffers received wastewater at a 1X rate (600 kg N ha-1 year-1), two at a 3/4X rate (450 kg N ha-1 year-1), and two served as controls. The wastewater was applied to the 10 m grassed portion of the buffers. Transects of shallow groundwater wells starting at the grass-forest interface and running downslope were used to monitor water quality N. The study showed mixed results concerning N assimilation by the buffers. Upslope land use changes by the producer during the study added significant N inputs to one set of buffers, and they were unable to assimilate sufficient N from both these inputs and the wastewater to protect shallow groundwater quality. In contrast, almost all samplings of shallow groundwater under the buffers receiving N only from the overland flow applied swine lagoon effluent showed nitrate (NO3-N) concentrations 20 and 30 m downslope to be lower than 10 mg L-1 (drinking water standard). On these buffers, NO3-N concentrations in shallow groundwater were near background levels five years after wastewater application commenced. The study indicated that the ratio of buffer area width to wastewater application area width on the landscape should be at least 1:1, and that buffers for protection of water quality should be continuous on the landscape. It was concluded from the study that buffers can be used at the farm scale to assimilate N from applied wastewater when they are sufficiently wide relative to waste application area, rate, and other N sources at the farm scale.

Abundance of non-target pests in transgenic Bt-maize: A farm scale study

The impact of transgenic Bt-maize, expressing the Cry1Ab protein, on aphids, leafhoppers, cutworms and wireworms was evaluated at the farm scale by comparing their abundance on Bt-plots and those sown with the isogenic variety over three consecu- tive growing seasons. The impact of Bt-maize was different on each of the three-herbivore groups. There were significantly more aphids on the Bt-maize but in terms of aphid species, the difference was only statistically significant for Sitobion avenae and not for the other three most abundant species (Metopolophium dirhodum, Rhopalosiphum padi and Macrosiphum euphorbiae). The analysis of aphid age structure showed consistently more individuals on Bt-plots; differences were significant for alates, apterous adults and young nymphs of R. padi, apterous adults and apterous fourth instar nymphs of S. avenae, alates, apterous adults and apterous fourth instar nymphs of M. dirhodum. Leafhoppers (Zyginidia scutellaris), particularly mature nymphs, were also more abundant on the Bt- maize. In spite of this there was no difference in leafhopper damage to Bt and non Bt-maize. The reasons for this are unclear but may be due to changes in Bt-maize that favoured aphids and leafhoppers. Differences in aphid and leafhopper densities were not high enough to affect yield. However, they may have affected the availability of prey for polyphagous predators such as Orius sp. The Bt- maize did not affect the incidence of cutworms (Agrotis segetum) or wireworms (Agriotes lineatus). These results indicate that Bt- maize does not have a negative impact on the non-target maize biocenosis at the farm scale.

Impact of farm-scale Bt maize on abundance of predatory arthropods in Spain

Transgenic maize expressing the Cry1Ab toxin from Bacillus thuringiensis (Bt-maize) has been grown in Spain since 1998, representing about 5% of the total maize area. As part of a Spanish specific monitoring program for Bt maize, a farm-scale study was initiated in 2000 to assess the potential impacts of Bt maize on predatory arthropods. The trials were conducted at two maize growing areas (Lleida and Madrid) over 3 years. In each locality three treatments (each with 3–4 replicates of 0.4–0.7 ha) were arranged in a completely randomised block design, Bt-maize (cv. Compa CB) being compared with the isogenic cv. Dracma under conventional farm practices, with or without the insecticide (imidacloprid) seed treatment. Predator abundance was monitored from late May to mid September in Lleida and from mid June to mid September in Madrid by visual surveys and pitfall traps. Anthocoridae, Coccinellidae, and Araneae represented about 90% of the total number of predators recorded in visual samplings whereas Carabidae and Araneae were the two prevalent predator groups (85–90% of the total predators) collected in pitfall traps. Their abundance varied from year to year and between locations, but no clear tendencies related to Bt maize was recorded. Insecticide treatment reduced anthocorid numbers occasionally but no consistent effects were found for the rest of predators. Our data suggest that Bt maize is compatible with the naturally occurring predators.

A Systems Approach to Assess Farm-scale Nutrient and Trace Element Dynamics: A Case Study at the Öjebyn Dairy Farm

A systems analysis approach was used to assess farmscale nutrient and trace element sustainability by combining full-scale field experiments with specific studies of nutrient release from mineral weathering and trace-element cycling. At the Ojebyn dairy farm in northern Sweden, a farm-scale case study including phosphorus (P), potassium (K), and zinc (Zn) was run to compare organic and conventional agricultural management practices. By combining different element-balance approaches (at farmgate, barn, and field scales) and further adapting these to the FARMFLOW model, we were able to combine mass flows and pools within the subsystems and establish links between subsystems in order to make farm-scale predictions. It was found that internal element flows on the farm are large and that there are farm internal sources (Zn) and loss terms (K). The approaches developed and tested at the Ojebyn farm are promising and considered generally adaptable to any farm.

A farm-scale study on the use of clinoptilolite zeolite and De-Odorase ® for reducing odour and ammonia emissions from broiler houses

Intensive poultry farms are frequently the subject of odour complaints and are also known emitters of ammonia. In this paper an experiment is described which compared the effectiveness of two abatement compounds, clinoptilolite and De-Odorase ®, when used in broiler production. Two sites were used which had almost identical buildings, each with two rooms, and the same strain of bird. Clinoptilolite was used on one site and De-Odorase ® on the other. Once a week ventilation rate, ammonia concentration and odour concentration were measured, to determine the effects of the additives. We also measured temperature, relative humidity and carbon dioxide concentration to confirm that the control and test rooms had similar micro-climates. In the room treated with clinoptilolite the ammonia concentration was statistically significantly higher than in the control and the total mass of ammonia emitted was 50% greater. In the De-Odorase ® experiment the mean ammonia concentration in the treated room in the final week was 38% lower than in the control and the total mass of ammonia emitted from the treated room was 50% lower. There was no statistically significant reduction in the odour concentration or odour emission rate for either of the additives used.

A farm scale study on the use of De-Odorase ® for reducing odour and ammonia emissions from intensive fattening piggeries

An experiment was mounted at a large fattening piggery in Slovenia, during which different groups each of 600 weaned pigs were housed and grown in different fattening rooms for 60 days (from age 24 days to age 84 days). All rooms were mechanically ventilated and had fully-slatted floors with slurry channels beneath. De-Odorase ® † † De-Odorase is a registered trademark of Alltech Biotechnology Center. was added to the diet of the treated groups of pigs at the rates recommended by the suppliers, e.g. for grower feed, 65 g/t. De-Odorase ® was also added daily (3·2 g suspended in 10 l of water) to the upstream ends of the slurry channels. Once a week, the ammonia concentration in the air inside each fattening room was measured at each of four positions, using Dräger tubes, and the ventilation rate was computed from the cross-sectional area of each fan outlet and the average velocity of the air emerging from each. Also, air samples were taken from immediately outside three of the fans serving each room, and their odour concentrations were measured by olfactometry. Hence, weekly values of emission rates of both ammonia and odour could be calculated. Ammonia concentration was significantly lower ( P = 0·001) in the De-Odorase ®-treated buildings than in the control buildings. The average reduction in ammonia concentration over a 7 week period was 26%. Ammonia emission rate was also reduced by 26% through the use of the additive. This reduction was significant at P = 0·048. Neither odour concentration nor odour emission rate was significantly reduced through the use of the additive. The additive did not significantly influence the rate of live-weight gain by the pigs.

Agronomy of Dryland Corn Production at the Northern Fringe of the Great Plains

The farming systems of the semi-arid northern Great Plains, including the Canadian Prairies, suffer from overdependence on a narrow range of crops, particularly wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Diversification of economically competitive cropping would greatly enhance the long-term viability and sustainability of agriculture in this large and important region of North America. The expansion of corn (Zea mays L.) production into the coolest and driest fringe of the northern Great Plains (e.g., southern Alberta) represents one attempt at diversification. This expansion has largely been on irrigated land, but semi-arid dryland production of corn appears promising. Eight years of research on dryland corn in southern Alberta focused on hybrid evaluation, irrigated and dryland comparisons, genotypic responses to drought and density stress, optimum plant density, paired row studies, weed control trials, and a 3-yr farm-scale study of three corn-based rotations. Grain yields of 35 bu/acre on summerfallow were obtained with currently available hybrids for the 2840 growing-degree-day (GDD) area around Medicine Hat in southern Alberta. Hybrids that yielded well on irrigation tended to yield well on dryland, and the hybrid most tolerant of stress on dryland had a short anthesis-to-silking interval. Optimum plant densities on dryland are about 12 000 plants/acre, compared with 24 000 on irrigation (annual rainfall of 14 to 16 in.). Dryland yields were more variable than irrigated yields; the lowest yields on dryland were 31 bu/acre (37% of the highest yields), whereas with irrigation the lowest yields were 81 bu/acre (66% of the highest yields). Averaged over five location-year combinations, paired rows (two rows 8 in. apart on 30-in. centers) resulted in a 10 bu/acre advantage over conventional 30-in. rows. The low crop density on dryland allowed late flushes of Russian thistle (Salsola iberica Sennen and Pau) and kochia, [Kochia scoparia (L.) Schrad.] to flourish. A herbicide combination to control this was identified: pre-plant atrazine combined with postemergence 2,4-D. Rotation results indicated that corn after corn yielded 18 bu/acre vs. 35 bu/acre for corn after fallow (similar to cereal yields). Corn shows potential as an alternative dryland crop on the fringes of the northern Great Plains, and may find its place either in a corn-fallow rotation or in a winter wheat-corn-fallow rotation.