Dale Bumpers Small Farms Research Center

Abstract Soils that contain high P levels can become a primary source of dissolved reactive P (DRP) in runoff, and thus contribute to accelerated eutrophication of surface waters. In a previous study on Captina soil, several soil test P (STP) methods gave results that were significantly correlated to DRP levels in runoff, but distilled H 2 O and NH 4 ‐oxalate methods gave the best correlations. Because results might differ on other soils, runoff studies were conducted on three additional Ultisols to identify the most consistent STP method for predicting runoff DRP levels, and determine effects of site hydrology on correlations between STP and runoff DRP concentrations. Surface soil (0–2 cm depth) of pasture plots was analyzed by Mehlich III, Olsen, Morgan, Bray‐Kurtz P1, NH 4 ‐oxalate, and distilled H 2 0 methods. Also, P saturation of each soil was determined by three different methods. Simulated rain (75 mm h −1 ) produced 30 min of runoff from each plot. All correlations of STP to runoff DRP were significant ( P < 0.01) regardless of soil series or STP method, with most STP methods giving high correlations ( r > 0.90) on all three soils. For given level of H 2 O‐extractable STP, low runoff volumes coincided with low DRP concentrations. Therefore, when each DRP concentration was divided by volume of plot runoff, correlations to H 2 O‐extractable STP had the same ( P < 0.05) regression line for every soil. This suggests the importance of site hydrology in determining P loss in runoff, and may provide a means of developing a single relationship for a range of soil series.

OBJECTIVE: To determine prevalence of anthelmintic resistance on sheep and goat farms in the southeastern United States. DESIGN: Cross-sectional study. ANIMALS: Sheep and goats from 46 farms in 8 southern states, Puerto Rico, and St Croix in the US Virgin Islands. PROCEDURES: Parasite eggs were isolated from fecal samples, and susceptibility to benzimidazole, imidathiazole, and avermectin-milbemycin anthelmintics was evaluated with a commercial larval development assay. RESULTS: Haemonchus contortus was the most common parasite on 44 of 46 farms; Trichostrongylus colubriformis was the second most commonly identified parasite. Haemonchus contortus from 45 (98%), 25 (54%), 35 (76%), and 11 (24%) farms were resistant to benzimidazole, levamisole, ivermectin, and moxidectin, respectively. Resistance to all 3 classes of anthelmintics was detected on 22 (48%) farms, and resistance to all 3 classes plus moxidectin was detected on 8 farms (17%). CONCLUSIONS AND CLINICAL RELEVANCE: Findings provided strong evidence that anthelmintic resistance is a serious problem on small ruminant farms throughout the southeastern United States. Owing to the frequent movement of animals among regions, the prevalence of resistance in other regions of the United States is likely to also be high. Consequently, testing of parasite eggs for anthelmintic resistance should be a routine part of parasite management on small ruminant farms.

After a brief history of ergot alkaloids and ergotism, this review focuses on the metabolism and mechanisms of action of the ergot alkaloids. The authors provide models of how these alkaloids afflict grazing livestock under complex animal-plant/endophyte-environmental interactions. Alkaloid chemistry is presented to orient the reader to the structure-function relationships that are known to exist. Where appropriate, the medical literature is used to aid interpretation of livestock research and to provide insight into potential modes of action and alkaloid metabolism where these are not known for livestock. In closing the paper, we discuss management of ergot alkaloid intoxication in livestock and future research needs for this field of study.

Soil microorganisms play essential roles in soil organic matter dynamics and nutrient cycling in agroecosystems and have been used as soil quality indicators. The response of soil microbial communities to land management is complex and the long-term impacts of cropping systems on soil microbes is largely unknown. Therefore, changes in soil bacterial community composition were assessed in response to cropping sequences and bio-covers at long-term no-tillage sites. Main effects of four different cropping sequences of corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean (Glycine max L.) were rotated in four year phases for 12-yrs at two Tennessee Research and Education Centers in a randomized complete block design with split-block treatments of four winter bio-covers: hairy vetch (Vicia villosa L.), wheat (Triticum aestivum L.), poultry litter, and a fallow control. Using Illumina high-throughput sequencing of 16S rRNA genes, bacterial community composition was determined. Composition, diversity, and relative abundance of specific taxa were correlated per cropping system, bio-cover, and their interaction. We found that i) richness and diversity varied temporally and spatially, coinciding with soil carbon, pH, nutrient levels, and climatic variability; ii) community composition varied by cropping system, with continuous corn, soybean, and the corn-soybean rotation presenting a hybrid of the continuous corn and soybean communities; however, continuous cotton resulted in the most varied assemblage; iii) bio-covers asserted the greatest influence on microbial communities; specifically poultry litter treatments differed from cover crops (all of which received inorganic-N). Consequently, microbial diversity was greatest under nutrient rich bio-covers (poultry litter) and high residue producing, less pesticide-intensive cropping sequences (soybean and corn compared to cotton), suggesting a more dynamic soil ecology under these no-till cropping systems. This suggests that nutrient management (inorganic fertilizers vs. animal manure) and greater crop rotations (within 4-yr phases) may directly drive phylogenetic community structure and subsequent ecosystem services across agricultural landscapes.

Carbon stored in soils contributes to a variety of soil functions, including biomass production, water storage and filtering, biodiversity maintenance, and many other ecosystem services. Understanding soil organic carbon (SOC) spatial distribution and projection of its future condition is essential for future CO2 emission estimates and management options for storing carbon. However, modeling SOC spatiotemporal dynamics is challenging due to the inherent spatial heterogeneity and data limitation. The present study developed a spatially explicit prediction model in which the spatial relationship between SOC observation and seventeen environmental variables was established using the Cubist regression tree algorithm. The model was used to compile a baseline SOC stock map for the top 30 cm soil depth in the State of Wisconsin (WI) at a 90 m × 90 m grid resolution. Temporal SOC trend was assessed by comparing baseline and future SOC stock maps based on the space-for-time substitution model. SOC prediction for future considers land use, precipitation and temperature for the year 2050 at medium (A1B) CO2 emissions scenario of the Intergovernmental Panel on Climate Change. Field soil observations were related to factors that are known to influence SOC distribution using the digital soil mapping framework. The model was validated on 25% test profiles (R2: 0.38; RMSE: 0.64; ME: −0.03) that were not used during model training that used the remaining 75% of the data (R2: 0.76; RMSE: 0.40; ME: −0.006). In addition, maps of the model error, and areal extent of Cubist prediction rules were reported. The model identified soil parent material and land use as key drivers of SOC distribution including temperature and precipitation. Among the terrain attributes, elevation, mass-balance index, mid-slope position, slope-length factor and wind effect were important. Results showed that Wisconsin soils had an average baseline SOC stock of 90 Mg ha−1 and the distribution was highly variable (CV: 64%). It was estimated that WI soils would have an additional 20 Mg ha−1 SOC by the year 2050 under changing land use and climate. Histosols and Spodosols were expected to lose 19 Mg ha−1 and 4 Mg ha−1, respectively, while Mollisols were expected to accumulate the largest SOC stock (62 Mg ha−1). All land-use types would be accumulating SOC by 2050 except for wetlands (−34 Mg C ha−1). This study found that Wisconsin soils will continue to sequester more carbon in the coming decades and most of the Driftless Area will be sequestering the greatest SOC (+63 Mg C ha−1). Most of the SOC would be lost from the Northern Lakes and Forests ecological zone (−12 Mg C ha−1). The study highlighted areas of potential C sequestration and areas under threat of C loss. The maps generated in this study would be highly useful in farm management and environmental policy decisions at different spatial levels in Wisconsin.

Abstract Plant–pollinator interactions are mediated by floral signals and by the quantity and quality of floral rewards. Biotic and abiotic disturbances can influence plant reproductive success through both direct effects on plant performance and indirect effects on pollinator attraction. In this study, we examined the effects of drought on buckwheat ( Fagopyrum esculentum Moensch), a globally cultivated plant that is prone to drought stress, dependent on insect pollinators for reproduction, and increasingly utilized in on‐farm conservation. Between drought‐stressed and control plants, we compared: nectar quantity and chemical composition, pollen quantity, floral volatile emissions, visits by both managed and wild pollinators, and plant reproductive success. Drought‐stressed plants produced significantly fewer flowers and less nectar per flower, though pollen quantity per flower was unaffected. Nectar from drought‐stressed plants had a lower proportion of sucrose relative to total sugars, though overall sugar concentration was unaffected. Significantly fewer bumble bees, honey bees, and flies were recorded on drought‐stressed plants. While there was no significant difference in the quantity of total floral volatile emissions, volatile compositions differed, with drought‐stressed plants having higher emissions of ( Z )‐3‐hexenol, isobutyraldehyde, 2‐methylbutanal, and 3‐methylbutanal. Finally, drought stress had negative effects on seed set and total seed mass per plant. Our results show that drought stress can have significant effects on floral traits and pollinator attraction, reducing plant reproductive success, and the nectar resources available to pollinators. Thus, the potential value of this plant in pollinator conservation and as a honey plant may be reduced under drought stress.

Soil organic matter (SOM) is one of the most important soil-forming factors and complex with a chemical composition not fully known. The amount of SOM traditionally is estimated by stoichiometric determination of carbon dioxide (CO2) released from oxidation reaction with a chromium mixture, hence the term soil organic carbon (SOC). The two most common oxidation methods are Tyurin (T) and Walkley-Black (WB). However, the efficiency of organic carbon oxidation depends upon the conditions of the oxidation reduction (redox) reaction (temperature, reagent concentration, oxidation time), which vary for both methods. The lack of consistent results from the oxidation methods has led to widely different conversion factors. Although the Tyurin’s method has been slowly removed from some laboratories, there still remains a large number of samples, especially from Eurasia, that have been measured by this method for more than a century and continue at the present time. The objective of this research was to develop equations or pedotransfer functions (ptf) for converting SOC determined by the Tyurin method to current and more widely used methods, such as WB and dry combustion (DC). A comparative analysis was performed for the assessment of soil organic carbon content obtained by Tyurin and Walkley-Black methods for ten quality control soil samples and 100 field soil samples. The selected soils differed in their genesis, geographical origin, and organic carbon content. SOC determined by dry combustion, providing a maximum oxidation of organic carbon, was used as a standard for comparing Tyurin and WB methods. The conversion factors from Corg by DC developed from equations (ptf) were 1.15 and 1.30 for WB and Tyurin methods. The SOM measurement error for both methods did not exceed 20%. The relationship between the absorption of calibration solutions and the mass of sucrose carbon or the equivalent amount of iron (II) for the entire OC range in this study was very strong (r = 0.99). The values of the calibration function coefficients (A0, K) of the calibration functions A = A0 + Km (OC) for both methods, did not depend upon the nature of the reducing agent. The relative error of the K coefficients when using two reducing agents (Mohr’s salt or sucrose) was not more than δ2 ≤ 2.5%. Soil samples prepared using the Tyurin method experienced additional dispersion compared to the Walkley-Black method, which caused higher values in the measurement of SOC even after centrifugation of soil suspensions. The mean SOC measured value by the Tyurin method combined with 48 h settling time was comparable with the mean SOC measured by dry combustion. The established coefficients ensure that the results are transferable and consistent with the standard method. The results from this study facilitate the integration of the accumulated data that are analyzed by different methods across the Eurasian countries into one comprehensive database that could be incorporated into the global network for monitoring soil quality and carbon stocks

Poultry litter provides a rich source of nutrients for perennial forages, but the usual practice of surface-applying litter to pastures can degrade water quality by allowing nutrients to be transported from fields in surface runoff, while much of the NH4-N volatilizes. Incorporating litter into the soil can minimize such problems in tilled systems, but has not been used for perennial forage systems. In this study, we minimized disturbance of the crop, thatch, and soil structure by using a knifing technique to move litter into the root zone. Our objective was to determine effects of poultry litter incorporation on quantity and quality of runoff water. Field plots were constructed on a silt loam soil with well-established bermudagrass [Cynodon dactylon (L.) Pers.] and mixed grass forage. Each plot had 8 to 10% slopes, borders to isolate runoff, and a downslope trough with sampling pit. Poultry litter was applied (5.6 Mg ha(-1)) by one of three methods: surface-applied, incorporated, or surface-applied on soil-aeration cuts. There were six treatment replications and three controls (no litter). Nutrient concentrations and mass losses in runoff from incorporated litter were significantly lower (generally 80-95% less) than in runoff from surface-applied litter. By the second year of treatment, litter-incorporated soils had greater rain infiltration rates, water-holding capacities, and sediment retention than soils receiving surface-applied litter. Litter incorporation also showed a strong tendency to increase forage yield.

Soybean mosaic virus (SMV) is a major viral pathogen, affecting soybean [Glycine max (L.) Merr.] production worldwide. The Rsv3 gene of soybean confers resistance to three of the most virulent strains (G5-G7) of SMV. The objectives of this study were to map Rsv3 and develop polymerase chain reaction (PCR) based markers for marker-assisted selection (MAS) purposes. Disease-response data were collected from two F(2) mapping populations, L29 (Rsv3) x Lee68 (rsv3) and Tousan 140 (Rsv3) x Lee68 (rsv3). Bulk segregant analysis based on amplified fragment length polymorphism (AFLP) markers demonstrated that the Rsv3 locus maps to the soybean molecular linkage group (MLG) B2 between restriction fragment length polymorphism (RFLP) markers A519 and Mng247. These two tightly linked RFLP markers were converted to PCR-based markers to expedite MAS. Sequence analysis of the Mng247 genomic region revealed similarity to the consensus sequence of a leucine-rich repeat (LRR) characteristic of the extracellular LRR class of disease resistance genes. Results from this study will be useful in pyramiding viral resistance genes and in cloning the Rsv3 gene.

ABSTRACT Knowledge of genetic diversity and relationships among breeding materials has a significant impact on crop improvement. Association between parental divergence and progeny performance has not been well documented in cotton ( Gossypium hirsutum L.). The objectives of this study were to estimate genetic diversity among selected cotton genotypes on the basis of simple sequence repeat (SSR) markers, and to investigate the relationship between genetic diversity and F 2 ‐bulk population performance. Five U.S. and four Australian cultivars, and two day‐neutral converted lines of G. hirsutum were genotyped by means of 90 SSR primer pairs providing 69 polymorphic marker loci. Genetic distance (GD) between genotypes ranged from 0.06 to 0.34 for the 11 parental genotypes. The highest GD (0.34) was observed between ST474 and the day‐neutral converted line B1388. The lowest GD (0.06) was detected between cultivars FM832 and FM975. The GD between day‐neutral converted lines and cultivars ranged from 0.26 to 0.34. Among the Australian cultivars, GD ranged from 0.06 to 0.19 while GD among U.S. cultivars varied from 0.10 to 0.22, indicating a narrow genetic base. Significant correlations between agronomic and fiber traits of F 2 ‐bulk populations and GD ranged from negative to positive depending on the traits, genetic background, and environment. On the basis of SSR markers, GD revealed a lack of genetic diversity among all genotypes and it was a poor predictor of overall F 2 performance. However, when genotypes with maximum range of GD were present, it was a better predictor for some traits.

Since the onset of land application of poultry litter, transportation of microorganisms, antibiotics, and disinfectants to new locations has occurred. While some studies provide evidence that antimicrobial resistance (AMR), an evolutionary phenomenon, could be influenced by animal production systems, other research suggests AMR originates in the environment from non-anthropogenic sources. In addition, AMR impacts the effective prevention and treatment of poultry illnesses and is increasingly a threat to global public health. Therefore, there is a need to understand the dissemination of AMR genes to the environment, particularly those directly relevant to animal health using the One Health Approach. This review focuses on the potential movement of resistance genes to the soil via land application of poultry litter. Additionally, we highlight impacts of AMR on microbial ecology and explore hypotheses explaining gene movement pathways from U.S. broiler operations to the environment. Current approaches for decreasing antibiotic use in U.S. poultry operations are also described in this review.

Color Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with endophyte (Neotyphodium coenophialum) infected (E+) or noninfected (E−) tall fescue seed. Eighteen crossbred (Angus ×Brangus) heifers were assigned to 6 pens and were fed chopped alfalfa hay for 5 d and chopped alfalfa hay plus a concentrate that contained E−tall fescue seed for 9 d during an adjustment period. An 11-d experimental period followed, with animals in 3 pens fed chopped alfalfa hay plus a concentrate with E+ seed and those in the other 3 pens fed chopped hay plus concentrate with E E−seed. Color Doppler ultrasound measurements (caudal artery area, peak systolic velocity, end diastolic velocity, mean velocity, heart rate, stroke volume, and flow rate) and serum prolactin were monitored during the adjustment (baseline measures) and during the experimental period. Three baseline measures were collected on d 3, 5, and 6 during the adjustment period for comparison to post E+ seed exposure. Statistical analyses compared the proportionate differences between baseline and response at 4, 28, 52, 76, 100, 172, and 268 h from initial feeding of E+ seed. Serum prolactin concentrations on both diets were lower (P <0.001) than baseline beginning at 4 h from the start of the experimental period. However, trends in serum prolactin concentrations for heifers on the E−diet suggested ambient temperature was affecting these concentrations. Caudal artery area in E+ heifers had declined (P <0.10) from baseline by 4 h and was consistently lower (P <0.05) for the remainder of the period. Heart rates for E+ heifers were lower than the baseline rate from 4 (P <0.10) to 100 (P <0.001) h, but were similar (P >0.10) to the baseline for 172 and 268 h measures. Blood flow in E+ heifers was consistently lower than the baseline from 4 (P <0.05) to 172 (P <0.001) h, but was similar to the baseline at 268 h when heart rate was similar to the baseline rate. Caudal artery areas for the E−diet were similar to baseline areas except at 100 h when it was greater than baseline. Heart rates and flow rates for E−heifers did not differ (P >0.10) from baseline measures during the experimental period. Results indicated that onset of toxicosis was within 4 h of cattle exposure to E+ tall fescue and is related to vasoconstriction and reduction in heart rate.

Reliable estimations of soil organic carbon (SOC) deficits in agroecosystems are crucial in evaluating the atmospheric C sequestration potential of agricultural soils and supporting management decisions. Nonetheless, the co-benefit on soil quality resulting from SOC accrual is rarely considered. Here, we assessed SOC saturation and soil physical quality in permanent grasslands (PG) and croplands (CR) by applying the C-saturation concept and the SOC:clay ratio as an indicator of soil physical quality to a set of long-term monitoring sites in western Switzerland. For this goal, we produced a new relationship between the silt + clay (SC) particles and the C stored in the mineral-associated fraction (MAOMC) and we assessed the assumption that grasslands can be used as C-saturated reference sites. The saturation in PG was not coincidental as it depended on the C accrual history. Hence, PG with the lowest MAOMC have not reached their C-saturation level and present a potential SOC storage under optimal management. The MAOMC saturation in CR was low (62 ± 4%) and corresponded to a deficit of −8.8 ± 1.2 mg C g−1 soil as compared to the current level in PG. The saturation was mainly affected by the proportion of temporary grassland in the crop rotation. The relative distribution of C between MAOM (∼80%) and the fine and coarse particulate organic matter (POM) was not affected by land-use types. The MAOMC saturation in this study (MAOMC = 0.372 × SC + 4.23) was similar to that reported in the litterature, but discrepancies appeared when the silt and clay contents were considered separately. SC was by far the main factor explaining MAOMC amount in PG (semi-partial R2: 0.66). In contrast to other studies, the C content of MAOM in PG (43 mg C g−1 SC) was not related to the SC content, suggesting a fixed maximal value in C-saturated soils. Nonetheless, MAOMC saturation may be underestimated as the least saturated PG might still accumulate MAOMC. Finally, the SOC:clay ratio was correlated with MAOMC saturation level in CR, but not in PG suggesting that targeting SOC accrual in CR optimizes the benefits between soil C storage and soil quality.

Spatial heterogeneity in environmental factors on the land surface moderates exchanges of water, energy, and greenhouse gases between the land and the atmosphere. However, appropriately representing this heterogeneity in earth system models remains a critical scientific challenge. We used a large dataset of environmental factors (n = 31) representing soil-forming factors, field observations of soil organic carbon (SOC) (n = 6213), and a machine-learning algorithm (Cubist) to analyze the scaling behavior of SOC across the conterminous United States. We found that various environmental factors are significant predictors of SOC stocks at different spatial scales. Out of the 31 environmental factors we investigated, only 13 were significant predictors of SOC stocks at spatial scales ranging from 100 m to 50 km. Overall, topographic variables had higher influence at finer scales, whereas climatic variables were more important at coarser scales. The model performance worsened with increasing scale or the spatial resolution of prediction (R2 = 0.38–0.65). The strength of environmental controls (median regression coefficient) on SOC weakened with scale, and we represented them using mathematical functions (R2 = 0.38–0.98). Both the mean and variance of SOC stocks decreased linearly with increasing the scale in soils of the conterminous United States. Fitted linear functions accounted for 81% and 82% of the variability in the mean and variance of SOC, respectively. We also found linear relationships among mean and high-order moments of SOC (R2 = 0.51–0.97). Improved understanding of the scaling behavior of SOC stocks and their environmental controllers can improve earth system model benchmarking and may eventually improve representation of the spatial heterogeneity of land surface biogeochemistry.

The inclusion of cover crops in cropping systems brings direct and indirect costs and benefits. Farmers will adopt and utilize cover crops as long as the perceived benefit of using them is positive. This paper examines the demographic and management factors affecting the adoption and perceived benefit (in terms of improved crop yield) of using winter annual cover crops. A double selectivity model of cover crop adoption and perceived yield gain was estimated using survey data of Alabama farmers examining cover crop use and management. Results may help in understanding factors shaping farmers' perceptions, adoption, and retention of cover crops.

Elucidating complex interactions of cover crops and crop residues on soil physicochemical properties is critical to sustaining soil productivity long-term. Our objective was to compare soil strength and chemistry (physiochemical), cover crop residue composition, and soil compaction following 15-years of cropping system implementation under non-tillage. Main effects were cropping sequences of soybean (Glycine max L.), corn (Zea mays L.), and cotton (Gossypium hirsutum L.), grown on a Loring silt loam, and sequences of corn and soybean on a Maury silt loam. Split-block treatments consisted of winter wheat (Triticum aestivum L.), Austrian winter pea (Pisum sativum L. sativum var. arvense) and hairy vetch (Vicia villosa Roth) cover crops, as well as poultry litter, and a fallow control. Soil physicochemical characteristics were evaluated at surface (0–15 cm) and sub-surface (15–30 cm) depths. Overall, soil physicochemical parameters were more affected by long-term cover crops and poultry litter in surface layers, whereas crop rotations impacted soil chemistry at sub-surface layers. High-nitrogen (N) containing cover crops had more desirable composition for soil biota (less recalcitrant), whereas corn had the highest soil carbon (C), N, and C:N ratio, likely owing to the greatest amount of residue being produced under this cropping sequence. Whole profile (0–1.2 m) assessment of soil compaction indicates: continuous cotton > continuous soybean > corn-soybean > continuous corn > corn-cotton, likely owing to greater planting and spraying traffic throughout the cotton production cycle. Study results help identify cropping system management effects on soil physicochemical properties under no-tillage and such data are needed for quantifying soil quality per soil conservation management.

Soil microorganisms are important for maintaining soil health, decomposing organic matter, and recycling nutrients in pasture systems. However, the impact of long-term conservation pasture management on soil microbial communities remains unclear. Therefore, soil microbiome responses to conservation pasture management is an important component of soil health, especially in the largest agricultural land-use in the US. The aim of this study was to identify soil microbiome community differences following 13-years of pasture management (hayed (no cattle), continuously grazed, rotationally grazed with a fenced, un-grazed and unfertilized buffer strip, and a control (no poultry litter or cattle manure inputs)). Since 2004, all pastures (excluding the control) received annual poultry litter at a rate of 5.6 Mg ha −1 . Soil samples were collected at a 0–15 cm depth from 2016–2017 either pre or post poultry litter applications, and bacterial communities were characterized using Illumina 16S rRNA gene amplicon sequencing. Overall, pasture management influenced soil microbial community structure, and effects were different by year ( P &lt; 0.05). Soils receiving no poultry litter or cattle manure had the lowest richness (Chao). Continuously grazed systems had greater ( P &lt; 0.05) soil community richness, which corresponded with greater soil pH and nutrients. Consequently, continuously grazed systems may increase soil diversity, owing to continuous nutrient-rich manure deposition; however, this management strategy may adversely affect aboveground plant communities and water quality. These results suggest conservation pasture management (e.g., rotationally grazed systems) may not improve microbial diversity, albeit, buffer strips were reduced nutrients and bacterial movement as evident by low diversity and fertility in these areas compared to areas with manure or poultry litter inputs. Overall, animal inputs (litter or manure) increased soil microbiome diversity and may be a mechanism for improved soil health.

Reproductive development in sexual plants is substantially more sensitive to high temperature stress than vegetative development, resulting in negative implications for food and fiber production under the moderate temperature increases projected to result from global climate change. High temperature exposure either during early pollen development or during the progamic phase of pollen development will negatively impact pollen performance and reproductive output; both phases of pollen development are considered exceptionally sensitive to moderate heat stress. However, moderately elevated temperatures either before or during the progamic phase can limit fertilization by negatively impacting important pollen pistil interactions required for successful pollen tube growth toward the ovules. This minireview identifies the impacts of heat stress on pollen-pistil interactions and sexual reproduction in angiosperms. A special emphasis is placed on the biochemical response of the pistil to moderately high temperature and the resultant influence on in vivo pollen performance and fertilization.

Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with endophyte (Neotyphodium coenophialum) noninfected (E-, 0 microg of ergovaline/g of DM), a 1:1 mixture of endophyte-infected and E- (E+E-; 0.39 microg of ergovaline/g of DM), or endophyte-infected (E+, 0.79 microg of ergovaline/g of DM) tall fescue (Lolium arundinaceum) seed. Eighteen crossbred (Angus x Brangus) heifers [345 +/- 19 kg (SD)] were assigned to individual pens and fed chopped alfalfa hay plus a concentrate that contained E- tall fescue seed for 7 d during an adjustment period. A 9-d experimental period followed with feeding treatments of chopped alfalfa hay plus a concentrate with E+, E-, or E+E- seed being assigned randomly to pens. Doppler ultrasound measurements (caudal artery luminal area, peak systolic velocity, end diastolic velocity, mean velocity, heart rate, and flow rate) and serum prolactin were monitored during the adjustment (3 baseline measures) and during the experimental period (7 measures). Statistical analyses compared proportionate differences between baseline and responses at 3, 27, 51, 75, 171, and 195 h from initial feeding of the experimental diets. Serum prolactin concentrations for E+ and E+E- diets were less (P < 0.001) than baseline concentrations beginning at 27 and 51 h, respectively, from initial feeding of the diets. Although baseline measures were taken when ambient temperatures were likely below thermoneutrality, caudal artery luminal cross-sectional area in E+ heifers had declined (P = 0.004) from baseline by 27 h and remained less (P < 0.02) until 195 h, and caudal artery luminal area declined (P = 0.004) in E+E- heifers from baseline by 51 h and remained less (P < 0.07) until 171 h. Blood flow rate was slower than the baseline rate at 51 h for E+ (P = 0.058) and E+E- (P = 0.02 heifers, but blood flow remained slower in E+E- heifers for 48 h, whereas it remained slower in E+ heifers for 96 h. Adjustments in artery luminal area and blood rate with the 3 diets appeared to parallel the increases in ambient temperature. Heifers fed a diet containing a larger amount of ergot alkaloids had less of a response to ambient temperature than heifers consuming the diet with less or no ergot alkaloids.

Unnecessary accumulation of phosphorus (P) in agricultural soils continues to degrade water quality and linked ecosystem services. Managing both soil loss and soil P fertility status is therefore crucial for eutrophication control, but the relative environmental benefits of these two mitigation measures, and the timescales over which they occur, remain unclear. To support policies toward reduced P loadings from agricultural soils, we examined the impact of soil conservation and lowering of soil test P (STP) in different regions with intensive farming (Europe, the United States, and Australia). Relationships between STP and soluble reactive P concentrations in land runoff suggested that eutrophication control targets would be more achievable if STP concentrations were kept at or below the current recommended threshold values for fertilizer response. Simulations using the Annual P Loss Estimator (APLE) model in three contrasting catchments predicted total P losses ranging from 0.52 to 0.88 kg ha −1 depending on soil P buffering and erosion vulnerability. Drawing down STP in all catchment soils to the threshold optimum for productivity reduced catchment P loss by between 18 and 40%, but this would take between 30 and 40+ years. In one catchment, STP drawdown was more effective in reducing P loss than erosion control, but combining both strategies was always the most effective and more rapid than erosion control alone. By accounting for both soil P buffering interactions and erosion vulnerability, the APLE model quickly provided reliable information on the magnitude and time frame of P loss reduction that can be realistically expected from soil and STP management. Greater precision in the sampling, analysis, and interpretation of STP, and more technical innovation to lower agronomic optimum STP concentrations on farms, is needed to foster long‐term sustainable management of soil P fertility in the future. Core Ideas Sensitive management of soils and soil P fertility is critical for limiting water quality degradation. Maintaining soil test P (STP) at or below the agronomic optimum reduces the eutrophication threat. STP drawdown in combination with erosion control reduced catchment P loss by up to 62%. The APLE model quickly quantified the magnitude and timescale of potential P loss reductions.