Automated Rainout Shelter Research Articles

Response of Retail Lawn Seed Products during Acute Drought and Recovery

Consumers often have multiple choices when purchasing retail lawn products in stores. In this study, we evaluated the acute drought performance of locally available retail lawn seed products (mixtures or blends) at two mowing heights of 2.5 and 3 inches. We hypothesized that the species present in the products and the height-of-cut differentially influence the drought resistance and recovery of the mixtures and blends. In Fall 2016 and 2017, 28 different products consisting of 25 mixtures and 3 blends of turfgrass seeds were established under a fully automated rainout shelter at the St. Paul campus of the University of Minnesota. The drought treatments lasted for 67 days in 2017, and 52 days in 2018; both the 2017 and 2018 treatments were followed by a recovery period. Data were obtained during acute drought treatments and recovery periods for visual turfgrass quality and green turfgrass cover using digital images of the plots. During the first year, several products displayed higher green stability (or the ability to remain green) at the 3-inch height-of-cut compared with the 2.5-inch height-of-cut. Products with tall fescue (Schedonorus arundinaceus) and fine fescue (Festuca sp.) as dominant species generally performed better during the drought treatments, whereas an increasing presence of perennial ryegrass (Lolium perenne) and kentucky bluegrass (Poa pratensis) decreased the visual drought performance of the products. During the recovery period, an effect of the interaction between mowing height and the date of data collection on the percentage of green cover was observed: the lower mowing height improved the early recovery of green cover after acute drought. These findings suggest that consumers in the upper midwestern United States and areas with a climate similar climate to that of St. Paul, MN, who are challenged with multiple choices of lawn seed products should choose products containing a higher tall fescue content and adjust their mowing heights to optimize recovery.

Design of Automated Rainout Shelter to Conduct Experiment on Drought Tolerant Maize Genotype

Uneven and low precipitation areas of Nepal are continuously suffering from drought and received low productivity because of unavailability of suitable drought tolerant maize genotype. An attempt has been made first time in Nepal by constructing an automated rainout shelter with soil moisture based automated drip irrigation system at National Maize Research Program in 2018-2019 to conduct an experiment on drought tolerant maize genotype. The rainout shelters automatically covers the cropping area as soon as the rain sensor received a single drop of precipitation and also if the light intensity decreased to value set in the control panel. Likewise, the soil water level in different treatments were maintained on the basis of the treatment controlled with automatic drip irrigation system set to irrigate at threshold value set in the microcontroller. The complete system had found very useful in determining accurate amount of water required to cultivate drought tolerant maize genotype. We have tested drought tolerant variety RampurSo3Fo8 under 10 level of irrigation and it was determined that 495.2 mm of water is maximum level of water to produce highest yield of 3.32 t/ha whereas 445.6 mm to 247.6 mm of water could can be manage to produce competitive yield without any reduction. An experiment under such kind of infrastructure provide useful information on irrigation management practices required for drought variety in the natural environment. The research output also guides farmers and agriculturist in making Nepalese agricultural more sustainable, mechanized and productive.

The impact of seed deficiency on productivity and on negative drought effect in semi‐natural grassland

AbstractQuestionsVegetative re‐sprouting and recruitment from seed determine grassland recovery after severe drought, but the mechanisms determining vegetation composition are not fully understood. We ask how the timing of drought and seed availability modify the drought legacy effects on composition and function in a temperate, semi‐natural grassland.LocationNegrentino, southern Alps, Switzerland.MethodsUnder automated rainout shelters, we simulated extreme seasonal drought events in a late summer and in the following spring, added rainwater to simulate normal conditions in no‐drought controls and maintained haymaking at times of normal practice. Towards the end of the summer drought, we added seeds of ten local species in a three‐factor split‐plot arrangement with seven blocks as the replicated unit. We measured fine‐scale variation in soil depth. We assessed the biomass of graminoids and forbs at regular harvesting dates and the species frequencies of established plants and recruits before treatment start, repeating these assessments for three years thereafter. We measured the biomass proportions of post‐drought annual recruit cohorts in year 4 after drought.ResultsOne‐time seed addition augmented recruits, modified species composition and enhanced species diversity; these effects propagated to increased reproductive shoots of recruits and community biomass four years later. Single and repeated seasonal droughts only caused low adult plant mortality but clearly reduced recruitment from seed, while post‐drought establishment was slightly enhanced. Seed augmentation compensated the negative spring drought effect on forb recruits and in turn mitigated the negative impact of drought on species diversity after drought.ConclusionsOur experiment shows that seed deficiency limits productivity and that seed deficiency compensation can help to stabilize diversity and productivity in semi‐natural grassland. Releasing the current constraints of management on seed supply in grassland would therefore assist in mitigating negative drought impacts.

Improved Wheat Growth and Yield by Delayed Leaf Senescence Using Developmentally Regulated Expression of a Cytokinin Biosynthesis Gene.

Delaying leaf senescence in plants, especially under water stress conditions, can help to maintain the remobilization of stored nutrients in source–sink relationships, thus leading to improved crop yields. Leaf senescence can be delayed by plant hormones such as cytokinin. Here, the Isopentenyl transferase (IPT) gene, encoding a cytokinin biosynthesis enzyme, driven by a modified AtMYB32xs promoter was transformed into wheat. Transgenic wheat plants exhibited delayed leaf senescence, retaining chlorophyll for longer under controlled environment conditions. Selected independent transgenic events and their corresponding nulls were grown under field conditions for two consecutive years under well-watered and water stress treatments using automated rainout shelters. Three independent transgenic events had improved canopy green cover, lower canopy temperatures, and higher leaf water potential than their respective non-transgenic nulls, with no abnormality in morphology and phenology. Increased grain yield was observed in transgenic events under both water treatments, with the yield increase more pronounced under water stress (26–42%). These results have shown that delayed leaf senescence using the chimeric transgene AtMYB32xs-p::IPT can be a useful strategy to achieve grain yield gains in wheat and potentially other crops for sustainable food production.

Nitrous Oxide Emissions from Turfgrass Receiving Different Irrigation Amounts and Nitrogen Fertilizer Forms

Nitrous oxide is an important greenhouse gas associated with global climate change. Turfgrasses emit N2O when fertilized with N and irrigated. The development of management practices such as use of controlled‐release N fertilizers and/or deficit irrigation may reduce N2O emissions in turf soils. The objectives of this study were (i) to quantify the magnitude and patterns of N2O emissions in turfgrass, and (ii) to determine how irrigation and N fertilization may be managed to reduce N2O fluxes. Nitrous oxide emissions were measured for 2 yr in ‘Meyer’ zoysiagrass (Zoysia japonica Steud.) under an automated rainout shelter in Manhattan, KS, using static chambers. Two irrigation levels (66 [medium] and 33% [low] reference evapotranspiration replacement), and three N fertilization treatments (urea and polymer‐coated urea [PCU], both applied at a rate of 98 kg N ha−1 yr−1, and an unfertilized plot) were included. During two summers, N2O emissions were reduced by 6% with low (2.71 kg ha−1) vs. medium irrigation (2.88 kg ha−1) (P ≤ 0.001). Over the 2 yr, cumulative N2O emissions averaged 4.06 kg ha−1 in unfertilized turf and 4.5 kg ha−1 in PCU‐treated turf, which represent reductions of 28 and 20%, respectively, from urea‐treated turf (5.62 kg ha−1) (P ≤ 0.01). Results from this study indicate that the use of a controlled‐release fertilizer, such as PCU, and/or lower irrigation reduces N2O emissions in turfgrass.

Automated Rainout Shelter's Design for Well‐Defined Water Stress Field Phenotyping of Crop Plants

Field phenotyping to identify water stress‐tolerant crop genotypes is challenging due to uncertainty in the timing of rainfall. Rainout shelters offer a way of establishing controlled water stress environments by excluding untimely rain events. Here, we present a detailed description of custom‐designed rainout shelters. These shelters are fully automated and portable. The rainout shelters were constructed from steel arch frames and polyethylene cladding, which move on plastic road barriers. The three connected shelters, each 20 × 10 m, are rain sensor activated, solar powered and equipped with a motion sensor camera for remote monitoring. These rainout shelters have proven to be effective tools for field water stress phenotyping.

RNA Sequencing of Contaminated Seeds Reveals the State of the Seed Permissive for Pre-Harvest Aflatoxin Contamination and Points to a Potential Susceptibility Factor.

Pre-harvest aflatoxin contamination (PAC) is a major problem facing peanut production worldwide. Produced by the ubiquitous soil fungus, Aspergillus flavus, aflatoxin is the most naturally occurring known carcinogen. The interaction between fungus and host resulting in PAC is complex, and breeding for PAC resistance has been slow. It has been shown that aflatoxin production can be induced by applying drought stress as peanut seeds mature. We have implemented an automated rainout shelter that controls temperature and moisture in the root and peg zone to induce aflatoxin production. Using polymerase chain reaction (PCR) and high performance liquid chromatography (HPLC), seeds meeting the following conditions were selected: infected with Aspergillus flavus and contaminated with aflatoxin; and not contaminated with aflatoxin. RNA sequencing analysis revealed groups of genes that describe the transcriptional state of contaminated vs. uncontaminated seed. These data suggest that fatty acid biosynthesis and abscisic acid (ABA) signaling are altered in contaminated seeds and point to a potential susceptibility factor, ABR1, as a repressor of ABA signaling that may play a role in permitting PAC.

Cotton Water Productivity and Growth Parameters in the Humid Southeast: Experimentation and Modeling

Abstract. A global challenge for the coming decades will be increasing food and fiber production with less water. This can be partially achieved by increasing water productivity (WP) or crop water use efficiency (WUE), i.e., yield or biomass produced per unit water used. Cotton ( L.) is a major rainfed and irrigated crop in the U.S. and worldwide. While there is abundant information on cotton water use and yield relationships in drier regions, relevant field data and modeling in humid regions is not well developed. Robust crop models help complement field experimentation and predict the impact of irrigation management on production. The Food and Agriculture Organization (FAO) of the United Nations has developed a crop model (AquaCrop) that has been parameterized for a number of crops including cotton, but not in a humid region. The objective of this study was twofold: (1) to quantify cotton water use and in-season biomass and growth parameters, and (2) to parameterize and validate AquaCrop to simulate cotton water use and productivity in the humid Southeast U.S., where water conservation and sustainability are emerging issues. Irrigation experiments were conducted from 2009 to 2011 under field conditions as well as under a newly installed automated rainout shelter at a Clemson University research site near Blackville, South Carolina. Extensive season-long soil, crop, and climate data were collected under irrigation regimes ranging from rainfed (i.e., no irrigation) to fully irrigated (i.e., meeting 100% of crop water needs). Season-long data collected in 2009 and 2011 under different irrigation regimes were used to parameterize the model. Cotton seasonal water use ranged from 320 mm at 33% irrigation to 718 mm at full irrigation, corresponding to average seed cotton yields of 2134 to 3682 kg ha -1 . Water use efficiency in the three years ranged from 0.48 to 0.71 kg of seed cotton per m 3 of water applied (irrigation and rainfall). Normalized water productivity for the local climate was nearly the same during the three years, averaging 12.5 g m -2 . Model parameterization was less demanding than expected, requiring adjustments of a few model parameters. Using the parameterized model with independent field data from 2010, the model simulated canopy cover, soil water content, aboveground dry biomass, and yield values that were highly correlated with measured values, with coefficients of determination (R 2 ) greater than 0.66. Seasonal crop water use was predicted within 5% for most treatments but underpredicted by as much as 18% for the 100% treatment at the shelter and for all irrigation treatments in 2010. The underprediction of crop water use corresponded to values of deep percolation simulated by AquaCrop. Field measurements were inadequate to verify deep percolation, but such measurements are suggested for future model investigations. Results of this study suggest that a properly parameterized AquaCrop model provides a useful tool to study yield response to water stress and evaluate the effects of drought and alternate management practices on productivity.

Response and Recovery Characteristics of Kentucky Bluegrass Cultivars to Extended Drought

During drought, authorities may impose water restrictions for irrigation with little regard for damage to turfgrass. Our objectives were to evaluate the performance of Kentucky bluegrass (Poa pratensis L.) (KBG) cultivars during a prolonged dry down and subsequent recovery in the transition zone near Manhattan, KS, USA. Irrigation was withheld from 30 bluegrasses for 82 days in 2010 and 62 days in 2011. Rainfall was excluded from the study area with an automated rainout shelter. Digital images were collected every one to two weeks during dry down and recovery to obtain percent green turfgrass coverage. All cultivars were predominantly brown (0 to 3% green cover) by the end of the 82‐day dry down in 2010, and less brown (7 to 27% green cover) by the end of the 62‐day dry down in 2011, probably because all plots inadvertently received 1.54 inches of precipitation during the 2011 dry down. All 30 bluegrasses recovered after lengthy dry downs in both years, but recovery was slower in 2010 because of greater drought stress during the longer dry down. Differences in performance were observed among cultivars during the dry downs and recoveries, but were inconsistent between years. Exceptions during the dry down were Apollo and Bedazzled, which lost green cover more slowly than other cultivars; Apollo also recovered more quickly after drought than other cultivars. Bluegrasses have excellent recuperative ability even after severe drought, and are good choices for areas where extended bans on turfgrass irrigation are possible.

Water Use Efficiency by Switchgrass Compared to a Native Grass or a Native Grass Alfalfa Mixture

Perennial grass systems are being evaluated as a bioenergy feedstock in the northern Great Plains. Inter-annual and inter-seasonal precipitation variation in this region will require efficient water use to maintain sufficient yield production to support a mature bioenergy industry. Objectives were to evaluate the impact of a May–June (early season) and a July–August (late season) drought on the water use efficiency (WUE), amount of water used, and biomass production in monocultures of switchgrass (Panicum virgatum L.), western wheatgrass (Pascopyrum smithii (Rydb.) A. Love), and a western wheatgrass–alfalfa (Medicago sativa L.) mixture using an automated rainout shelter. WUE was strongly driven by biomass accumulation and ranged from 5.6 to 7.4 g biomass mm−1 water for switchgrass to 1.06 to 2.07 g biomass mm−1 water used with western wheatgrass. Timing of water stress affected WUE more in western wheatgrass and the western wheatgrass–alfalfa mixture than switchgrass. Water deficit for the western wheatgrass–alfalfa mixture was 23 % lower than western wheatgrass (P = 0.0045) and 31 % lower than switchgrass (P < 0.0001) under the May–June stress water treatment, while switchgrass had a 37 and 38 % greater water deficit than did western wheatgrass or western wheatgrass–alfalfa mixture, respectively (P < 0.001) under the July–August water stress treatment. Water depletion was always greatest in the upper 30 cm. Switchgrass had greater WUE but resulted in greater soil water depletion at the end of the growing season compared to western wheatgrass and a western wheatgrass–alfalfa mixture which may be a concern under multi-year drought conditions.

Scheduling irrigation with a dynamic crop growth model and determining the relation between simulated drought stress and yield for peanut

A computer simulation model can be used as a tool to help explain the impact of drought stress on plant growth and development because it integrates the complex soil–plant-atmosphere system through a set of mathematical equations. The objectives of this study were to determine the impact of different irrigation scheduling regimes on peanut growth and development, to determine the capability of the CSM-CROPGRO-Peanut model to simulate growth and development of peanut, and to determine the relationship between yield and the two cumulative drought stress indices simulated by the peanut model. The CSM-CROPGRO-Peanut model was evaluated with experimental data collected during two field experiments that were conducted in four automated rainout shelters located at The University of Georgia, USA, in 2006 and 2007. Irrigation was applied when the simulated soil water content in the effective root zone dropped below a specific threshold value for the available soil water capacity (AWC). The irrigation treatments corresponded to irrigation thresholds (IT) of 30, 40, 60, and 90 % of AWC. The results showed that growth and development was reduced for the 30 and 40 % IT treatments which resulted in yield reductions that were 92 and 45 %, respectively, of the 90 % IT treatment. The Cropping System Model (CSM)-CROPGRO-Peanut model was able to accurately simulate growth and development of peanut grown under different irrigation treatments when compared to the observed data. We found an inverse relationship between the two simulated total cumulative drought stress indices for leaf growth (expansion) and photosynthesis and simulated pod yield. Knowing the cumulative drought stress value prior to harvest maturity could help with the prediction of potential harvestable yield.

Determining FAO-56 crop coefficients for peanut under different water stress levels

Accurate estimates of peanut (Arachis hypogaea L.) water requirements are needed for water conservation. The objective of this study was to evaluate the FAO-56 crop coefficients for peanut grown under various levels of water stress in a humid climate. Two experiments were conducted in three automated rainout shelters located at the University of Georgia Griffin Campus in Griffin, Georgia, USA in 2006 and 2007. Irrigation was applied when the modeled soil water content in the effective root zone dropped below a specific threshold of the available water content (AWC). The irrigation treatments corresponded to irrigation thresholds (IT) of 40, 60 and 90% of AWC. The soil water balance was used to compute observed evapotranspiration (ETcm) from measured soil water content at six different soil depths. The length of the four developmental stages was different than the values listed in FAO-56. The 2-year average absolute relative error of Kcini was 8, 19 and 6% for 40, 60 and 90% IT, respectively. For the 90% IT, the FAO-56 Kcmid and Kcend were almost identical to the 2-year averages of the observed Kcmid and Kcend, respectively. The findings of this study confirmed that the FAO-56 procedure was reasonably accurate for estimating peanut ET under water stress in a humid climate.

Evaluation of FAO-56 crop coefficient procedures for deficit irrigation management of cotton in a humid climate

The use of the FAO-56 reference evapotranspiration (ET o) approach for irrigation scheduling has been recommended worldwide because it provides reasonable results under a wide range of climatic conditions. The crop ET (ET c) can be obtained from ET o using a stage-dependent crop coefficient ( K c). The latter depends on canopy height and crop–soil surface resistance and albedo. The objective of this study was to evaluate the FAO-56 K c procedure under different deficit drip irrigation treatments for cotton grown in a humid climate. A cotton experiment was conducted in 2005 in three automated rainout shelters located at the University of Georgia Campus in Griffin, GA, USA. When the modeled soil water content in the effective root zone dropped below a specific threshold of the available water content (AWC), irrigation was applied until the soil water reached 100% of AWC. The irrigation treatments were 40, 60, and 90% irrigation thresholds (IT). For instance, for the 40% IT treatment irrigation was applied when the modeled soil water content dropped to permanent wilting point plus 40% of the total available soil water. Thus, the least irrigated treatment corresponded to the 40% IT and the most irrigated corresponded to the 90% IT. The observed daily ET c was estimated from daily soil moisture readings. The length of the initial, development, and mid-stages were the same among the different treatments. However, the length of the late-stage for the 40 and 60% IT was 5 and 3 days less than that for the 90% IT, respectively. The observed K c for the initial stage was 0.51, 0.9, and 0.99 for the 40, 60, and 90% IT, respectively. The FAO-56 K c for this stage was within a few percent from the observed K c. For the mid-stage, the 60 and 90% IT had a similar value for K c (about 1.2) which was higher than the 40% IT (0.92). The end of season K c for the 40% IT (0.1) was lower than for the 60% IT (0.38), which in turn was lower than the 90% IT (0.58). The FAO-56 proved to be an accurate method for estimating cotton ET c under deficit irrigation. The values for the initial, mid, and end K c and the length of the different developmental stages for the 90% IT can be used in humid climates for fully irrigated cotton. The use of such information will help in effective irrigation planning and more precise water management.

Interactive Effects of Drought and Grazing on Northern Great Plains Rangelands

Drought is common in rangeland environments and an understanding of its impacts on the structure and function of rangeland ecosystems is paramount for developing effective management strategies. This research was the second of a series of studies investigating the impacts of varying seasonal droughts on northern Great Plains rangelands. Research was conducted on native rangeland during the 1998 through 2001 growing seasons. Study plots were twelve 5 × 10 m nonweighing lysimeters. An automated rainout shelter was used to establish drought conditions on 6 lysimeters during April, May, and June of 1998 and 1999. Single-day, flash grazing events were imposed at the beginning of May, June, and July. Grazing treatments were 1) graze during the 2 years of drought and the year after; 2) graze during the 2 years of drought and rest the year after; and 3) rest all years. Results showed that the intense spring drought reduced soil water content in the upper 30 cm of the soil profile and subsequently reduced total herbage production 20% to 40%; cool-season perennial grasses were the primary contributor to the reduction and cool-season annual grasses were secondary. Periodic grazing during drought had minimal impact on herbage production, whereas impacts on nondrought plots ranged from moderate enhancement to moderate suppression, with effects varying depending on functional group. Results also showed that substantial recovery occurred during the 1st postdrought year, with near full recovery realized within 2 years.

Interactive Effects of Drought and Grazing on Northern Great Plains Rangelands

Drought is common in rangeland environments and an understanding of its impacts on the structure and function of rangeland ecosystems is paramount for developing effective management strategies. This research was the second of a series of studies investigating the impacts of varying seasonal droughts on northern Great Plains rangelands. Research was conducted on native rangeland during the 1998 through 2001 growing seasons. Study plots were twelve 5 3 10 m nonweighing lysimeters. An automated rainout shelter was used to establish drought conditions on 6 lysimeters during April, May, and June of 1998 and 1999. Single-day, flash grazing events were imposed at the beginning of May, June, and July. Grazing treatments were 1) graze during the 2 years of drought and the year after; 2) graze during the 2 years of drought and rest the year after; and 3) rest all years. Results showed that the intense spring drought reduced soil water content in the upper 30 cm of the soil profile and subsequently reduced total herbage production 20% to 40%; cool-season perennial grasses were the primary contributor to the reduction and cool-season annual grasses were secondary. Periodic grazing during drought had minimal impact on herbage production, whereas impacts on nondrought plots ranged from moderate enhancement to moderate suppression, with effects varying depending on functional group. Results also showed that substantial recovery occurred during the 1st postdrought year, with near full recovery realized within 2 years.

Drought and Grazing: IV. Blue Grama and Western Wheatgrass

An understanding of the impacts of grazing during and following drought on rangeland ecosystems is critical for developing effective drought management strategies. This study was designed to examine the effects of drought and grazing on blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] and western wheatgrass [Pascopyrum smithii Rydb. (Love)] tiller growth dynamics. Research was conducted from 1993 to 1996 at the Fort Keogh Livestock and Range Research Laboratory located near Miles City, Mont. An automated rainout shelter was used during 1994 to impose a severe late spring to early fall (May to October) drought on 6 of twelve, 5- x 10-m non-weighing lysimeters. Twice replicated grazing treatments were: 1) grazed both the year of (1994) and the year after (1995) drought; 2) grazed the year of and rested the year after drought; and 3) no grazing either year. Drought had minimal impact on tiller relative growth rates of plants grazed twice, although it reduced (P less than or equal to 0.01) rates of axillary tiller emergence for blue grama (79%) and western wheatgrass (91%), respectively. Defoliation periodically increased relative growth rates (P less than or equal to 0.05) and tiller emergence (P less than or equal to 0.01) of both species. Neither drought nor grazing affected tiller densities or tiller replacement rates of either species nor did they affect productivity of blue grama. Drought, however, reduced (P less than or equal to 0.01) productivity of western wheatgrass 50% in 1994 whereas grazing reduced productivity (P less than or equal to 0.01) by 46% in 1994 and 69% in 1995. Moderate stocking levels (40-50% utilization) during and after drought did not adversely affect the sustainability of these dominant native grasses. DOI:10.2458/azu_jrm_v55i1_eneboe

Drought and grazing: IV. Blue grama and western wheatgrass

An understanding of the impacts of grazing during and following drought on rangeland ecosystems is critical for developing effective drought management strategies. This study was designed to examine the effects of drought and grazing on blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] and western wheatgrass [Pascopyrum smithii Rydb. (Love)] tiller growth dynamics. Research was conducted from 1993 to 1996 at the Fort Keogh Livestock and Range Research Laboratory located near Miles City, Mont. An automated rainout shelter was used during 1994 to impose a severe late spring to early fall (May to October) drought on 6 of twelve, 5- x 10-m non-weighing lysimeters. Twice replicated grazing treatments were: 1) grazed both the year of (1994) and the year after (1995) drought; 2) grazed the year of and rested the year after drought; and 3) no grazing either year. Drought had minimal impact on tiller relative growth rates of plants grazed twice, although it reduced (P less than or equal to 0.01) rates of axillary tiller emergence for blue grama (79%) and western wheatgrass (91%). Defoliation periodically increased relative growth rates (P less than or equal to 0.05) and tiller emergence (P less than or equal to 0.01) of both species. Neither drought nor grazing affected tiller densities or tiller replacement rates of either species nor did they affect productivity of blue grama. Drought, however, reduced (P less than or equal to 0.01) productivity of western wheatgrass 50% in 1994 whereas grazing reduced productivity (P less than or equal to 0.01) by 46% in 1994 and 69% in 1995. Moderate stocking levels (40-50% utilization) during and after drought did not adversely affect the sustainability of these dominant native grasses.

Drought and grazing: IV. Blue grama and western wheatgrass

An understanding of the impacts of grazing during and following drought on rangeland ecosystems is critical for developing effective drought management strategies. This study was designed to examine the effects of drought and grazing on blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] and western wheatgrass [Pascopyrum smithii Rydb. (Love)] tiller growth dynamics. Research was conducted from 1993 to 1996 at the Fort Keogh Livestock and Range Research Laboratory located near Miles City, Mont. An automated rainout shelter was used during 1994 to impose a severe late spring to early fall (May to October) drought on 6 of twelve, 5- x 10-m non-weighing lysimeters. Twice replicated grazing treatments were: 1) grazed both the year of (1994) and the year after (1995) drought; 2) grazed the year of and rested the year after drought; and 3) no grazing either year. Drought had minimal impact on tiller relative growth rates of plants grazed twice, although it reduced (P less than or equal to 0.01) rates of axillary tiller emergence for blue grama (79%) and western wheatgrass (91%), respectively. Defoliation periodically increased relative growth rates (P less than or equal to 0.05) and tiller emergence (P less than or equal to 0.01) of both species. Neither drought nor grazing affected tiller densities or tiller replacement rates of either species nor did they affect productivity of blue grama. Drought, however, reduced (P less than or equal to 0.01) productivity of western wheatgrass 50% in 1994 whereas grazing reduced productivity (P less than or equal to 0.01) by 46% in 1994 and 69% in 1995. Moderate stocking levels (40-50% utilization) during and after drought did not adversely affect the sustainability of these dominant native grasses.

Drought and Grazing: IV. Blue Grama and Western Wheatgrass

An understanding of the impacts of grazing during and following drought on rangeland ecosystems is critical for developing effective drought management strategies. This study was designed to examine the effects of drought and grazing on blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] and western wheatgrass [Pascopyrum smithii Rydb. (Love)] tiller growth dynamics. Research was conducted from 1993 to 1996 at the Fort Keogh Livestock and Range Research Laboratory located near Miles City, Mont. An automated rainout shelter was used during 1994 to impose a severe late spring to early fall (May to October) drought on 6 of twelve, 5- x 10-m non-weighing lysimeters. Twice replicated grazing treatments were: 1) grazed both the year of (1994) and the year after (1995) drought; 2) grazed the year of and rested the year after drought; and 3) no grazing either year. Drought had minimal impact on tiller relative growth rates of plants grazed twice, although it reduced (P less than or equal to 0.01) rates of axillary tiller emergence for blue grama (79%) and western wheatgrass (91%), respectively. Defoliation periodically increased relative growth rates (P less than or equal to 0.05) and tiller emergence (P less than or equal to 0.01) of both species. Neither drought nor grazing affected tiller densities or tiller replacement rates of either species nor did they affect productivity of blue grama. Drought, however, reduced (P less than or equal to 0.01) productivity of western wheatgrass 50% in 1994 whereas grazing reduced productivity (P less than or equal to 0.01) by 46% in 1994 and 69% in 1995. Moderate stocking levels (40-50% utilization) during and after drought did not adversely affect the sustainability of these dominant native grasses. DOI:10.2458/azu_jrm_v55i1_eneboe

Drought and Grazing III: Root Dynamics and Germinable Seed Bank

Drought and herbivory frequently influence North American rangelands. While these influences may temporarily reduce vegetative cover, their mutual influence on the available seedbanks which might occupy new safe sites is unclear. We examine effects of drought and grazing upon pre- and post-drought plant root distribution and germinable seed bank to determine 1) if the response of root distributions to drought depends upon grazing use and 2) if the presence of germinable seeds is altered significantly by drought and grazing. Using twelve, 5 X 10 m non-weighing lysimeters with an automated rainout shelter, we documented root intercepts in situ using a minirhizotron from 1993-1996. Seed bank samples were incubated in a greenhouse to determine seedling emergence. Roots were fewer in shallow soil layers in grazed plots than ungrazed plots by the end of the study, irrespective of drought. Roots in deeper (Bw horizon) soil layers were fewer during drought, but were not influenced by grazing. Seed bank composition results suggest that perennial grasses were a small portion of the seed bank. Cool-season annual grass seeds accumulated after drought. Without drought, forb seed banks increased with grazing. Thus while shallow roots may decrease during drought, in the year following drought grazing may decrease aboveground net primary production, and allow large accumulations of cool-season annual grass seed in a northern mixed grass prairie. DOI:10.2458/azu_jrm_v54i3_hild