Dryland Cotton Research Articles

Impact of Cover Crop on Nutrient Losses in an Upland Soil

ABSTRACT Nutrient losses through leaching and surface runoff are the main problems in no-till upland soils in Mississippi. A two-year study was conducted in 2016 and 2017 on an Atwood silt loam soil to evaluate the impact of winter wheat (Triticum aestivum L.) cover crop (WCC) in no-till dryland cotton (Gossypium hirsutum L.) received poultry litter (PL) on nitrogen (N) and phosphorus (P) losses in leached and surface runoff water. Experimental design comprised a split-plot with a 2 × 2 treatment arrangement replicated 3 times. Treatments included WCC and winter fallow (WF) were assigned to the main plots, while PL at the rate of 6.7 and 0 Mg ha−1 was assigned to the subplots. Wheat was planted after harvesting cotton and leachates were collected from October to April using suction cup lysimeters. Surface runoff was collected from the edge of the plots. Nitrate-N concentrations in leachate samples were 45% and 21% less with WCC (9.9 and 17.2 mg L−1) than winter fallow (WF) (18.2 and 22 mg L−1) in the first and second year, respectively. Residual soil NO3-N concentration at the top 15 cm depth before planting cotton was 41% greater with WF than with WCC. In each year, runoff volume and water-soluble P (WP) concentrations were greater with WCC than with WF. It appears that the cover crop utilizes N during its growth period and slowly releases it for the subsequent crops as evidenced by greater cotton dry matter, lint yield, and cotton N uptakes mainly in the first year.

Carbon exchange of a dryland cotton field and its relationship with PlanetScope remote sensing data

Agricultural systems experience numerous management-associated events during the growing season that can significantly influence seasonal and annual carbon balances. Measurements of carbon fluxes from agricultural fields using micrometeorological techniques such as eddy covariance can improve our understanding of management and weather-driven changes in carbon budgets. In-situ carbon flux data are also valuable in developing remote sensing-based models for extrapolation of biome-specific carbon budgets to higher spatial scales. In this study, net ecosystem carbon dioxide exchange (NEE) was continuously measured for two years (2017 and 2018) from a cotton (Gossypium hirsutum) field in College Station, Texas, USA. The measured NEE was partitioned into assimilatory (Gross Primary Production, GPP) and respiratory (Ecosystem respiration, Reco) fluxes. There were substantial differences in carbon fluxes between the two years, which were driven by variations in meteorological conditions and growth of weeds. Due to dry conditions, growing season carbon uptake in 2018 was reduced (883 g C m−2) compared to 2017 (947 g C m−2). While the growing season of 2018 was dry, the post-harvest off-season was remarkably wet with nearly 68% of the annual precipitation occurring after harvest (848 mm). This favored aggressive growth of weeds, resulting in substantial off-season carbon uptake in 2018 (374 g C m−2 in 2018 compared to 100 g C m−2 in 2017). Overall, the site was a net carbon source (175 g C m−2) in 2017, whereas it was a slight carbon sink (-5 g C m−2) in 2018. A significant correlation was found between satellite-derived normalized difference vegetation index (NDVI) and GPP (R2 0.78 in 2017 and 0.72 in 2018). Given that correlation, it would be possible to broaden these results to the wider region by estimating GPP with satellite data.

Comparison of evapotranspiration methods in the DSSAT Cropping System Model: I. Global sensitivity analysis

Global sensitivity analysis (GSA) is useful for evaluating the responsiveness of agroecosystem models to input parameter adjustments. Evaluations of model sensitivity for diverse water status conditions and evapotranspiration (ET) algorithms will facilitate better use of models to provide water management recommendations. The objective of this study was to conduct a GSA to identify influential parameters in the Decision Support System for Agrotechnology Transfer (DSSAT) Cropping System Model (CSM), specifically using the CROPGRO-Cotton module with data from cotton field studies conducted in 2000, 2001, and 2008 at Bushland, Texas. The field studies tested fully-irrigated, deficit-irrigated, and dryland cotton production in a semi-arid environment. Using high performance computing resources, a GSA was conducted to evaluate the sensitivity of 24 model outputs with respect to 37 model input parameters. The GSA was conducted for six different ET methodologies available in the model. With first-order sensitivity indices <0.05, nearly half of the tested input parameters did not influence any model output for any of the tested simulation scenarios. Among the parameters with first-order sensitivity indices >0.05, eleven were cultivar parameters that controlled crop development and growth, and five were soil parameters that specified initial soil water conditions, soil water limits, drainage rate, and root growth characteristics. The influences of another soil parameter and one ET parameter were relevant only for the ET methods that required them. Large differences in sensitivity indices were found based on the choice between two soil water evaporation methods. In addition to providing insights for other applications of this model, the results specifically informed further efforts to evaluate the model using measured data from the Bushland cotton studies to compare performance among the six ET methods, as reported in a companion paper.

Insectivorous bats foraging in cotton crop interiors is driven by moon illumination and insect abundance, but diversity benefits from woody vegetation cover

Landscape and biophysical determinants of insectivorous bat activity and community composition in space and time are central to understanding how growers can maximise bat-mediated pest control services in crops. We measured community composition, abundance, richness and foraging attempts of insectivorous bats in the centre of dryland cotton crops using acoustic sampling. We examined how bat activity was related to woody vegetation in the surrounding landscape, prey insect abundance, distance to crop edge, size of field, proximity to waterbodies and moon illumination to better understand insectivorous bat diversity and foraging in crop interiors. We collected a total of 9467 acoustic files including 1198 foraging attempts (feeding buzzes) of at least 21 insectivorous bat species. The bat assemblage in cotton crop interiors (richness and diversity) was positively related to woody vegetation foliage cover within 5–10 km of the crop, as well as Lepidoptera and Hymenoptera abundance, but was negatively related to distance from the field edge into the crop and moon illumination. Increased feeding attempts were linked to increased Lepidoptera and Hemiptera on nights of high moon illumination (> 75 %). Bat activity and foraging was also higher during nights of increased insect abundance, particularly Lepidoptera, indicating that bats track food resources. Our results highlight the importance of managing bat roosting habitat at different landscape scales to enhance bat diversity and foraging in crop interiors and thus insect consumption. Given the high bat feeding activity on nights of high moon illumination and increased Hemiptera abundance, the timing of insecticide sprays to target pests, such as Hemipteran sucking bugs, could be scheduled on nights of low moon illumination. Such information is useful in identifying conservation priorities for the management of bats in intensively farmed agroecosystems and should facilitate habitat management by growers to maximise crop pest protection services in crop interiors.

Net return and risk analysis of winter cover crops in dryland cotton systems

AbstractWinter cover crop and no‐till are two promising conservation practices to reduce soil erosion and promote long‐term sustainability. This research evaluates the net returns of two different tillage methods and five cover crop treatments in dryland cotton (Gossypium hirsutum L.) production and identifies risk‐efficient tillage and cover crop management practices. Four‐year field experiments (2013−2016) were conducted for a continuous cotton production system under conventional tillage and no‐till without a cover crop, as well as no‐till with cover crops including winter wheat (Triticum aestivum L.), crimson clover (Trifolium incarnatum L.), Austrian winter field pea (Pisum sativum L.), hairy vetch (Vicia villosa Roth), and mixed cover crops. Results showed no statistical differences in lint yields (P = .98) or net returns (P = .82). No‐till with crimson clover decreased yield variation compared to conventional tillage, while hairy vetch and mixed cover crops increased yield variation. The average net returns were US$454 and $461 ha−1 for conventional tillage and no‐till without a cover crop, respectively. The average net returns ranged from $346 to $389 ha−1 for the cover crop treatments. Producers have a higher probability of getting a higher net return if switching from conventional tillage to no‐till. The risk analysis results showed that no‐till without a cover crop was the most preferred practice by risk‐neutral, somewhat and rather risk‐averse producers. For very and extremely risk‐averse producers, no‐till with crimson clover was the most preferred management practice.

Comparing dryland cotton upland fibre quality from on-board spindle and stripper harvesting systems

On-board spindle and brush type stripper round module harvest systems were evaluated on commercial field scale for dryland Upland cotton in Australia over two harvest seasons. Observations on harvester performance, including harvesting efficiency, harvest loss, seed cotton yield and lint turn out were conducted at three locations, during the 2017 and 2018 cotton growing seasons, with a single variety. Fibre quality was measured by High Volume Instrumentation (HVI™) and Advanced Fiber Information System (AFIS) and analysed to determine if there were any significant differences between the two harvesting systems. The stripper harvesters had higher productivity (i.e. hectares per hour), harvested more material with lower harvest loss than the spindle harvesters. The seed cotton harvested by the stripper systems contained plant material which resulted in a lower lint turn out than the spindle harvester although the yield in bales ha−1 was still higher. There were no significant differences in fibre quality as measured by the HVI except for colour and trash. The significant differences in colour and trash did not affect the economic return to the grower as the visual colour and trash grades were below, i.e. better than, the Australian base grade. There were also no significant differences in the fibre quality as measured by AFIS. It is hypothesised that the reasons for this was due to the appropriate timing and application of defoliation, harvesting when moisture content ≤ 12%, reduced leaf allowing for gentler ginning and mature fibre.

Optimizing Dryland Crop Management to Regional Climate via Simulation. Part I: U.S. Southern High Plains Cotton Production

Over semi-arid agricultural regions such as the U.S. Southern High Plains (SHP) producers of dryland crops need to know which management practices increase yields and decrease production risk. Here, a modelling approach is used to explore management options (MO) that increase dryland cotton yields and estimate those practice’s yield risk effects under current SHP climate conditions. To simulate current dryland yield variability, dense distributions of lint yield outcomes were generated using the CROPGRO-Cotton crop model driven by weather inputs from 21 SHP weather stations during 2005-2016. Management effects were explored by repeating simulations over 32 MOs defined by 4 planting dates, 4 planting densities, and applying or not applying nitrogen. Both earlier planting date and decreased plant density increased median simulated yields, with earlier planting having the greatest positive yield effects. The MO that produced the highest median lint yields planted on the earliest planting date (May 15), at the lowest density (3 plants m-1), and applied no nitrogen. Recent SHP field studies generally confirm the earlier planting date effect, but suggest insignificant yield effects for different seeding rates. Even so, negligible yield effects and lower input costs favor lower seeding densities from a profit standpoint. These crop simulations demonstrate a modelling-based method for climate-related agricultural risk management, and suggest mid-May planting dates and low plant densities as part of management practices that increase yields and profits in dryland SHP cotton production.

Comparison of Two Tillage Practices in a Semi‐Arid Cotton–Grain Sorghum Rotation

Cotton and sorghum yield were more dependent on precipitation than tillage management. No‐till produced a greater cotton and sorghum crop yield in some years. Economic analyses indicate a reduction of costs with no‐till versus conventional practices. Conventional tillage (CT) cropping systems in semiarid regions of south Texas are associated with soil degradation and increasing fuel costs. The objective of the study was to evaluate the effects of no‐till (NT) compared with CT on a dryland cotton (Gossypium hirsutum L.)–grain sorghum [Sorghum bicolor (L.) Moench] rotation system with respect to crop yields, yield stability, soil moisture and structure, and economics. The experiment (four replicated plots of each crop and tillage treatment annually) was conducted on a Vertisol at Corpus Christi, TX, from 2011 to 2015. Cotton yield was similar among tillage treatments, except for the drought year of 2013 when 86% greater yield occurred with NT and above average precipitation year of 2015 (15% greater yield for NT). Sorghum yield was impacted by tillage in 2012 when NT produced 33% greater yield than CT, whereas, in 2015, CT produced 28% greater yield. Yields were stable across crops and tillage treatment. Soil moisture was not impacted by tillage treatment; however, tillage caused bulk density to increase at 15‐ to 30‐cm depth compared with 0‐ to 15‐cm depth. All soil chemical properties remained constant, except NT had greater total soil N than CT in 2015. Cash costs for CT were greater than NT for both crops, and net cash farm income was positive only for NT cotton. No‐till is a viable alternative for dryland farmers in this region because of stable yields and increased income.

A financial analysis and life-cycle carbon emissions assessment of oil palm waste biochar exports from Indonesia for use in Australian broad-acre agriculture

ABSTRACTOil palm waste from South Sumatra may represent an abundant source of biochar for beneficial agronomic use in Australian broad-acre farming systems. Here a cost–benefit analysis and carbon footprint of biochar applied to three different Australian broad-acre crops are presented, covering application rates of between 1 and 40 Mg ha−1 and considering either the effect of the biochar on yield or the effect of the biochar on reduced fertilizer requirement. Yield and nutrient efficiency effects are assumed to be constant across all crops. Analysis reveals that empty fruit bunch biochar could be produced in South Sumatra and transported to the farm gate in Australia at a minimum acceptable sale price per Mg of USD $266 to the biochar manufacturer. Despite assumed uniformity of the biochar effect, the return on investment for the biochar user from the perspective of yield increase varied significantly by crop (sugarcane: 67% return on investment [ROI], irrigated cotton: 43% ROI, dry land cotton: −22% ROI, wheat: −72% ROI). The study found that the average carbon footprint in CO2e over 100 years was −691 kg Mg−1 biochar when used to influence crop yield, and −286 kg Mg−1 biochar when used to reduce fertilizer requirements.

Planting Geometry Effects on the Growth and Yield of Dryland Cotton

The declining Ogallala Aquifer beneath the Southern High Plains may necessitate dryland crop production and cotton (Gossypium hirsutum L.) is a well-adapted and potentially profitable alternative crop. The limited growing season duration of the Texas Panhandle and southwestern Kansas, however, imposes significant production risk due to incomplete boll maturation. Emphasizing earlier boll production that is usually confined to sites on lower fruiting branches may reduce risk, but offsetting high planting densities are needed to maintain desirable lint yield. Our objectives were to quantify planting: 1) row width and 2) in-row spacing effects on growth, yield, and fiber quality of dryland cotton. Field tests of row widths from 0.25 to 0.76 m and plant densities with in-row spacing ranging from 0.075 to 0.15 m were conducted from 1999 to 2005 on a nearly level Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) managed in a wheat (Triticum aestivum L.), cotton, fallow (W-Ctn-F) rotation. To expand the basis of comparison, cotton growth and yields were simulated using GOSSYM and long-term (1958-2000) weather records from Bushland, TX, as input for all combinations of 0.38 or 0.76 m row widths and plant spacing of 0.075, 0.10 and 0.15 m. Experimental and computer simulated plant height and harvested boll number increased significantly with increased row spacing and, occasionally, in-row plant spacing. Modeled lint yield for 0.38 m rows decreased by approximately 50% compared with the 582 kg·ha-1 yield for conventional row spacing, which was practically duplicated by field observations in 2001 and 2004. Measured fiber quality occasionally improved with conventional row spacing over ultra-narrow rows, but was unaffected by plant spacing. Because narrow rows and frequent plant spacing did not improve lint yield or fiber quality of dryland cotton, we do not recommend this strategy to overcome a thermally limited growing season.

An investigation of farm-scale adaptation options for cotton production in the face of future climate change and water allocation policies in southern Queensland, Australia

Modelling cotton production at the farm-scale provides insight into the importance of water management options in adapting to climate change, especially given the renewed focus of government policies on irrigation water access and allocations. Using an irrigated cotton farm in southern Queensland as a case study, we investigated two possible adaptation strategies in response to changes in water resources from projected climate change (CSIRO Mk3.5, A1FI scenario). The modelled farm produced irrigated cotton, wheat, maize, and non-irrigated sorghum. The adaptation Strategy 1 allowed the substitution of current (baseline) production system with a system of less intensive cotton (2m row spacing) and a maximum of 2 in-crop irrigations instead of 4. Whereas Strategy 2 allowed for the production option of dryland cotton in the rotation and implied as much 2m row spacing cotton planting as possible depending on the other cropping rules regardless of the state of water storages. These two strategies were examined using a bio-economic farm enterprise model by evaluating the effects of projected changes in yield, water use and farm profitability (gross margin, GM), which resulted from crops competing for resources (i.e. irrigation water). Results showed 14% less water available in the 2030s and 2050s compared to the baseline (1960–2010), as a result of climate change and water policy decisions, thereby reducing the input costs. Under Strategy 1 there were 12.1% and 4.4% yield decreases in 2030 and 2050, respectively; while under Strategy 2 the inter-annual yield variability and proportion of low yields (<5bales/ha) increased over the same periods. Without adaptation GMs were reduced by 27% and 43% in 2030 and 2050, respectively. Strategy 1 resulted in 8.8% increase and 15.8% decrease in 2030 and 2050, respectively. However with Strategy 2, GM increases were observed (49% and 12%, respectively in 2030 and 2050). Moreover, without appropriate adaptation options, the enterprise would have to reduce the area of irrigated cotton, causing reductions in farm business gross margins. Our findings suggested that decreased water availability would not significantly impact the cotton production system and profitability if suitable adaptation options are available.

Modeling the effects of management and elevation on West Texas dryland cotton production

As the Ogallala Aquifer depletes there is a need to identify management options that might make un-irrigated cotton production sustainable over the U.S. Southern High Plains (SHP). To explore those options, the CSM-CROPGRO-Cotton model was used to simulate the effects of planting options and elevation effects on SHP dryland cotton production. Of the management variables that define the 56 planting options simulated, planting date and density account for the most variability in median SHP yields. Cooler SHP growing seasons have the effect of reducing median lint yields relative to those simulated over the lower elevations of the nearby Rolling Plains. This effect is not as evident in median Rolling Plains yields, which suggests it can be traced to the cooler growing environment of the higher SHP elevations. Also, at both higher and lower elevations lower planting densities maximize median yields, while higher densities result in the lowest yields. These results suggest that the yield suppressing effect of the SHP region’s cooler growing conditions might be compensated for by planting early whenever possible and planting at lower densities. The clear decreasing effect on median yields at higher elevation also suggests the possibility of SHP cotton production moving to the lower elevations of the nearby Rolling Plains as Ogallala Aquifer levels drop.

Modeling the effects of land use change from cotton (Gossypium hirsutum L.) to perennial bioenergy grasses on watershed hydrology and water quality under changing climate

Assessing the impacts of biofuel-induced land use change on hydrology, water quality and crop yield under the current and future climate scenarios enables selection of appropriate land uses and associated best management practices under the changing climate. In this study, the impacts of land use change from cotton (Gossypium hirsutum L.) to perennial grasses in the Double Mountain Fork Brazos watershed in the Texas High Plains were assessed using the Soil and Water Assessment Tool (SWAT). While switchgrass (Panicum virgatum L.) was assumed to replace cotton in irrigated areas, dryland cotton was replaced by Miscanthus×giganteus under the hypothetical land use change scenarios. Climate change impacts were assessed based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections of 19 General Circulation Models (GCMs) under two Representative Concentration Pathway (RCP) emission scenarios of RCP4.5 and RCP8.5 during two 30-year periods of middle (2040–2069) and end (2070–2099) of the 21st century. Median irrigation water use of cotton was simulated to decrease by 41%–61% in the future when compared to historic (1994–2009) period based on projections by 19 GCMs. Under the future climate change scenarios, when compared to cotton, median annual irrigation water use by switchgrass reduced by 62%–89%. Simulated future median total nitrogen load decreased by 30%–40% under perennial grasses when compared to future cotton land use. The median irrigated switchgrass yield decreased by 16%–28%, but the median dryland Miscanthus yield increased by 32%–38% under the future climate change scenarios.

Assessing the hydrologic and water quality impacts of biofuel‐induced changes in land use and management

AbstractThe Southern High Plains (SHP) of Texas, where cotton (Gossypium hirsutum L.) is grown in vast acreage, and the Texas Rolling Plains (TRP), which is dominated by an invasive brush, honey mesquite (Prosopis glandulosa) have the potential for biofuel production for meeting the U.S. bioenergy target of 2022. However, a shift in land use from cotton to perennial grasses and a change in land management such as the harvesting of mesquite for biofuel production can significantly affect regional hydrology and water quality. In this study, APEX and SWAT models were integrated to assess the impacts of replacing cotton with Alamo switchgrass (Panicum virgatum L.) and Miscanthus × giganteus in the upstream subwatershed and harvesting mesquite in the downstream subwatershed on water and nitrogen balances in the Double Mountain Fork Brazos watershed in the SHP and TRP regions. Simulated average (1994–2009) annual surface runoff from the baseline cotton areas decreased significantly (P &lt; 0.05) by 88%, and percolation increased by 28% under the perennial grasses scenario compared to the baseline cotton scenario. The soil water content enhanced significantly under the irrigated switchgrass scenario compared to the baseline irrigated cotton scenario from January to April and August to October. However, the soil water content was depleted significantly under the dryland Miscanthus scenario from April to July relative to the baseline dryland cotton scenario. The nitrate‐nitrogen (NO3‐N) and organic‐N loads in surface runoff and NO3‐N leaching to groundwater reduced significantly by 86%, 98%, and 100%, respectively, under the perennial grasses scenario. Similarly, surface runoff, and NO3‐N and organic‐N loads through surface runoff reduced significantly by 98.9%, 99.9%, and 99.5%, respectively, under the post‐mesquite‐harvest scenario. Perennial grasses exhibited superior ethanol production potential compared to mesquite. However, mesquite is an appropriate supplementary bioenergy source in the TRP region because of its standing biomass and rapid regrowth characteristics.

Simulated Effects of Winter Wheat Cover Crop on Cotton Production Systems of the Texas Rolling Plains

Abstract. Interest in cover crops has been increasing in the Texas Rolling Plains (TRP) region, mainly to improve soil health. However, there are concerns that cover crops could potentially reduce soil water and thereby affect the yield of subsequent cash crops. Previous field studies from this region have demonstrated mixed results, with some showing a reduction in cash crop yield due to cover crops and others indicating no significant impact of cover crops on subsequent cotton fiber yield. The objectives of this study were to (1) evaluate the CROPGRO-Cotton and CERES-Wheat modules within the cropping system model (CSM) of the Decision Support System for Agrotechnology Transfer (DSSAT) for the TRP region, and (2) use the evaluated model to assess the long-term effects of growing winter wheat as a cover crop on water balances and seed cotton yield under irrigated and dryland conditions. The two DSSAT crop modules were calibrated using measured data on soil water and crop yield from four treatments: (1) irrigated cotton without a cover crop (CwoC-I), (2) irrigated cotton with winter wheat as a cover crop (CwC-I), (3) dryland cotton without a cover crop (CwoC-D), and (4) dryland cotton with a winter wheat cover crop (CwC-D) at the Texas A&amp;amp;M AgriLife Research Station at Chillicothe from 2011 to 2015. The average percent error (PE) between the CSM-CROPGRO-Cotton simulated and measured seed cotton yield was -10.1% and -1.0% during the calibration and evaluation periods, respectively, and the percent root mean square error (%RMSE) was 11.9% during calibration and 27.6% during evaluation. For simulation of aboveground biomass by the CSM-CERES-Wheat model, the PE and %RMSE were 8.9% and 9.1%, respectively, during calibration and -0.9% and 21.8%, respectively, during evaluation. Results from the long-term (2001-2015) simulations indicated that there was no substantial reduction in average seed cotton yield and soil water due to growing winter wheat as a cover crop. Keywords: CERES-Wheat, Cover crop, Crop simulation model, CROPGRO-Cotton, DSSAT, Seed cotton yield, Soil water.

Evaluation of Stable Isotopes of Water to Determine Rainwater Infiltration in Soils under Conservation Reserve Program

The Conservation Reserve Program (CRP) is a USDA program introduced in 1985 to reduce soil erosion by increasing vegetative cover of highly erodible land. Participation in the CRP is done via contracts (10 - 15 years in length) and currently the total area of land under contract is set to decline as per the 2014 Farm Bill. The Texas High Plains (THP) leads the US with >900,000 ha enrolled in CRP. A potential long- term benefit of CRP is to increase soil organic matter and to improve soil structure leading to increased water infiltration. Our objective was to evaluate the feasibility of using stable isotopes of water to measure and compare infiltration of rain in land under CRP management to land under continuous dryland cotton in the THP. For this purpose we selected two sites, with soils in the Amarillo series, enrolled in CRP, one for 25 years and the second site for 22 years. Results from several rain events showed that stable isotopes of water are a method that can be used to evaluate the depth of rainwater infiltration for soils under CRP and dryland management.

The cost effectiveness of a policy to store carbon in Australian agricultural soils to abate greenhouse gas emissions

Data for cropping and pastoral enterprises in south eastern Australia were used in a cost-effectiveness analysis to assess the feasibility of abating greenhouse gas (GHG) emissions through storing soil carbon (C) as soil organic matter under the Australian government's Carbon Farming Initiative. We used the C credit value for 2013-14 of $24.15 per tonne of CO2- equivalent (CO2-e) and a C storage rate of 0.5 tonne C/hectare/year for conversion of cropland to pasture. Given that a change of enterprise is driven primarily by farmer returns, we found that none of the changes were feasible at current prices, with the exception of wheat to cattle or sheep in an irrigated system, and dryland cotton to cattle or sheep. Given that our model scenario assumed the most favourable economic factors, it is unlikely that increased soil C storage through a change from cropping to pasture can make a significant contribution to abating Australia's CO2 emissions. However, of greater concern to society is the methane emissions from grazing cattle or sheep, which would negate any gain in soil C under pasture, except for a switch from dryland cropping to sheep.

Cotton Growth, Yield, and Fiber Quality Response to Irrigation and Water Deficit in Soil of Varying Depth to a Sand Layer

Research was conducted in 2010 and 2011 at the West Tennessee Research and Education Center in Jackson, TN to investigate irrigation response in cotton. The objective of this study was to evaluate plant response to four different irrigation regimes by using main-stem node counts, quantification of canopy light interception, and canopy temperature, while making comparisons across two soils that vary in depth to a sandy layer. PHY 375 WRF cottonseed was planted in a no-tillage system in 9-m rows on 97-cm spacing with 10.5-12 seed m-1 of row. Irrigation was applied from drip tape lying in the row furrow at rates of 0, 1.27, 2.54, and 3.81 cm week-1. Comparisons were made across deep soils (no sand layer within the top 89 centimeters of soil) and shallow soils (sand layer within the top 61 centimeters of soil). Plant height, number of nodes, nodes above white flower (NAWF), canopy light interception, and canopy temperature were monitored during the blooming period of the crop each year to determine differences in irrigation response. Cotton plants grown in deep soils had higher vegetative biomass, total number of nodes, plant height, light interception, fiber quality, yield, and reduced canopy temperature compared to plants grown in the shallow soil. Similarly, irrigation increased cotton plant vegetative biomass, total number of nodes, plant height, light interception, fiber quality, yield, and reduced canopy temperature compared to dryland cotton. Results from this trial indicate that differences in physiological growth patterns, canopy density, canopy temperature, lint yield, and fiber quality are evident when compared across irrigation amounts and soil depths.

Plant Growth Stage-Specific Injury and Economic Injury Level for Verde Plant Bug, &lt;I&gt;Creontiades signatus&lt;/I&gt; (Hemiptera: Miridae), on Cotton: Effect of Bloom Period of Infestation

Verde plant bugs, Creontiades signatus Distant (Hemiptera: Miridae), were released onto caged cotton, Cossypium hirsutum L., for a 1-wk period to characterize the effects of insect density and bloom period of infestation on cotton injury and yield in 2011 and 2012, Corpus Christi, TX. When plants were infested during early bloom (10-11 nodes above first white flower), a linear decline in fruit retention and boll load and a linear increase in boll injury were detected as verde plant bug infestation levels increased from an average of 0.5 to 4 bugs per plant. Lint and seed yield per plant showed a corresponding decline. Fruit retention, boll load, and yield were not affected on plants infested 1 wk later at peak bloom (8-9 nodes above first white flower), even though boll injury increased as infestation levels increased. Second-year testing verified boll injury but not yield loss, when infestations occurred at peak bloom. Incidence of cotton boll rot, known to be associated with verde plant bug feeding, was low to modest (< 1% [2012] to 12% [2011] of bolls with disease symptoms), and drought stress persisted throughout the study. Caging effect was minimal: a 10% fruit retention decline was associated with caging, and the effect was not detectable in the other measurements. Overall, reduced fruit retention and boll load caused by verde plant bug were important contributors to yield decline, damage potential was greatest during the early bloom period of infestation, and a simple linear response best described the yield response-insect density relationship at early bloom. Confirmation that cotton after peak bloom was less prone to verde plant bug injury and an early bloom-specific economic injury level were key findings that can improve integrated pest management decision-making for dryland cotton, at least under low-rainfall growing conditions.

Overview of the Bushland Evapotranspiration and Agricultural Remote sensing EXperiment 2008 (BEAREX08): A field experiment evaluating methods for quantifying ET at multiple scales

In 2008, scientists from seven federal and state institutions worked together to investigate temporal and spatial variations of evapotranspiration (ET) and surface energy balance in a semi-arid irrigated and dryland agricultural region of the Southern High Plains in the Texas Panhandle. This Bushland Evapotranspiration and Agricultural Remote sensing EXperiment 2008 (BEAREX08) involved determination of micrometeorological fluxes (surface energy balance) in four weighing lysimeter fields (each 4.7ha) containing irrigated and dryland cotton and in nearby bare soil, wheat stubble and rangeland fields using nine eddy covariance stations, three large aperture scintillometers, and three Bowen ratio systems. In coordination with satellite overpasses, flux and remote sensing aircraft flew transects over the surrounding fields and region encompassing an area contributing fluxes from 10 to 30km upwind of the USDA-ARS lysimeter site. Tethered balloon soundings were conducted over the irrigated fields to investigate the effect of advection on local boundary layer development. Local ET was measured using four large weighing lysimeters, while field scale estimates were made by soil water balance with a network of neutron probe profile water sites and from the stationary flux systems. Aircraft and satellite imagery were obtained at different spatial and temporal resolutions. Plot-scale experiments dealt with row orientation and crop height effects on spatial and temporal patterns of soil surface temperature, soil water content, soil heat flux, evaporation from soil in the interrow, plant transpiration and canopy and soil radiation fluxes. The BEAREX08 field experiment was unique in its assessment of ET fluxes over a broad range in spatial scales; comparing direct and indirect methods at local scales with remote sensing based methods and models using aircraft and satellite imagery at local to regional scales, and comparing mass balance-based ET ground truth with eddy covariance and remote sensing-based methods. Here we present an overview of the experiment and a summary of preliminary findings described in this special issue of AWR. Our understanding of the role of advection in the measurement and modeling of ET is advanced by these papers integrating measurements and model estimates.