1. Using satellite imagery to track spread of Old World bluestem in Kansas grasslands

Transcription

1 Number 223 December 18, Using satellite imagery to track spread of Old World bluestem in Kansas grasslands 1 2. Changes in soil carbon concentration and structural properties with deficit irrigation 3 3. Cover Your Acres Conference Set for Jan in Oberlin 7 1. Using satellite imagery to track spread of Old World bluestem in Kansas grasslands Old World bluestem (OWB) is a name used to describe both yellow OWB [Bothriochloa ischaemum (L.) Keng] and Caucasian bluestem [Bothriochloa bladhii (Retz) S.T. Blake]. Yellow OWB includes Turkestan bluestem and King Ranch bluestem. This species originates from northern Africa, Eurasia, and the Mediterranean. Caucasian bluestem is native to southern Asia and Australia. OWBs were introduced to the U.S. for conservation purposes and as a forage crop for haying and grazing. Seedings of OWBs in Kansas started in the 1930s and continued to some extent into the 1960s. In recent years OWBs have been used commonly in the southern Great Plains (Oklahoma and Texas) in grassland plantings and on Conservation Reserve Program (CRP) acres, but are not recommended for use in Kansas. Although a number of species are called bluestems, OWBs are not closely related to the native grasses little bluestem and big bluestem. Why are OWBs being used in Oklahoma and Texas, but not in Kansas? Cost of the seed, ease of establishment, and drought tolerance favors OWBs use in the southern Great Plains. In addition, OWBs are aggressive and prolific seed producers. Old world bluestems are adapted to high calcareous and high ph soils, and do well on any well- drained soil. But studies done in Kansas have indicated that OWB is lower in forage quality compared to native grasses and results in lower animal gains. It is unpalatable in comparison to desirable species. OWB can invade neighboring pastures 10 or more years after establishment. It can invade any time another species or mixture is overgrazed, stressed by drought or wildfire, or otherwise suppressed. Once OWB begins invading other pastures, it can be very difficult to control and manage. In Kansas, cattle will graze native grasses and leave the OWB almost untouched. Old World bluestem is much inferior in nutritional quality to little bluestem, big bluestem, Indiangrass, 1

2 switchgrass, sideoats grama, and other native grasses in Kansas. If OWB were to continue spreading on rangeland and pasture in Kansas, it could have a significant effect on cattle production. Old World bluestem is extremely invasive once it gets established. It is a bunch grass that spreads through seed dispersal. Where it becomes established, it grows in clumps, keeping other forages from becoming established and leaving significant amounts of soil unprotected and susceptible to erosion. Both photos above were taken on July 16, The photo on the left is of OWB showing its bunch grass nature compared to the more sod-forming nature of many of the native grasses. Notice in the OWB photo evidence of concentrated flow, rilling, and plant pedestalling with roots exposed at the surface. The native prairie photo at right shows a denser plant canopy and no evidence of soil erosion. In this photo, Walt Fick and Bethany Porter Gabrow, graduate student in Agronomy, are shown using a modified step-point sampling method to estimate plant species cover. Photos by Carol Blocksome, K-State Research and Extension. For these reasons and more, OWB is an undesirable forage grass in Kansas. It can be considered an invasive species. It can be controlled, but control becomes progressively more difficult and expensive the longer the grass is allowed to grow and spread. It is important, then, to know where OWB has become established in Kansas, and how far it has spread. To do this quickly and cheaply, we at the Department of Agronomy s Ecology & Agriculture Spatial Analysis Laboratory have begun investigating the use of satellite imagery to track this invasive species. Satellite imagery detects selected solar energy wavelengths that are differentially reflected and emitted by various types of land cover. The scanned imagery is then analyzed by computer to detect unique spectral patterns associated with different types of vegetation and vegetation conditions such as including vegetation health, quantity, and quality. In order to know what type of vegetation we are seeing when looking at satellite imagery of rangeland, we start by comparing imagery from a certain date with observations on the ground. We have taken observations at seven times during the growing season to record the spectral reflectance characteristics of OWB compared to other native prairie vegetation types in the visible (colors of the rainbow) and near and middle infrared wavelengths (730-2,500 nm) that are not discernable with the human eye. 2

3 In the case of OWB, its growth pattern is markedly different spectrally from other native grasses at various times of the year. This is true even though OWB and native grasses are all warm-season grasses. In June, for example, we have found there are significantly different spectral reflectance patterns between where there is OWB and native prairies dominated by native grasses. The biggest factor, however, is that of bare ground. Land dominated by OWB has much more bare ground for most of the growing season than land covered by native grasses. This information will allow us to better select the optimal times during the growing season when satellite images of the region can be used to identify areas of rangeland that dominated by OWB. The map below is from Google Earth. This is not strictly satellite imagery, but it shows how we can use remote sensing to identify areas of OWB. In this remote sensing map from Google Earth, the areas of OWB shows up clearly as an area of darker reddish brown in the center of the map. The dark "tendrils" in this map, by the way, are areas of red cedar. This is an image from an area of the Flint Hills just east of Tuttle Creek Reservoir, near Olsburg. -- Kevin Price, Professor of Remote Sensing, Natural Resources, GIS -- Bethany Porter Grabow, Agronomy Graduate Student -- Walt Fick, Rangeland and Pasture Management Specialist 2. Changes in soil carbon concentration and structural properties with deficit irrigation Supplemental irrigation is one of the potential practices to enhance carbon (C) sequestration in cultivated soils. This is particularly true when irrigation is combined with no-till and intensive cropping systems. Irrigation can increase soil C sequestration by 10 to 50% in some cases by 3

4 increasing crop biomass production -- depending on soil type, irrigation frequency, and cropping system. On the other hand, this gain in C accumulation is offset to some extent by faster soil organic matter decomposition through increased soil water content and biological activity due to irrigation. Studies have, for example, shown that C dioxide fluxes from irrigated soils are often greater than from nonirrigated soils. Irrigation also requires energy for pumping, which results in an increase in CO 2. This also offsets some of the C sequestered in the soil. In particular, the effects of deficit irrigation (also called limited irrigation) on soil organic and inorganic C sequestration, as well as soil physical properties, have not been well documented. Quantifying changes in soil C concentration as influenced by deficit irrigation is critical for assessing global C cycles. At K-State, we measured soil organic and inorganic C concentration and selected soil physical properties for two deficit irrigation experiments in western Kansas in spring Two linear-move sprinkler irrigation experiments, established at Garden City in 2004 and Tribune in 2001, were studied. There were six irrigation treatments at Garden City and three at Tribune. At Garden City, the irrigation amounts within the same level of treatment varied from year to year, depending on the rainfall amount and evapotranspiration rates. At this site, the amount of irrigation water applied averaged across 5 yr (from 2004 to 2008) for the six irrigation treatments was 66, 86, 117, 152, 182, and 217 mm, respectively. At Tribune, the irrigation amounts for the three treatments were 127, 254, and 381 mm per year, respectively. At this site, irrigation amounts remained constant each year. The cropping system was winter wheat-grain sorghum-sunflower-corn-corn at Garden City and sunflower-grain sorghum-soybean-corn at Tribune. These crop rotations were managed under no-till and each phase of the rotation was present each year. Measurements were taken prior to the second corn crop in the Garden City rotation and during the corn phase in the Tribune rotation. Deficit irrigation and organic and inorganic C concentration Deficit irrigation had moderate effects on soil organic C but had no effects on inorganic C concentration (Table 1). Effects on C concentration were, however, significant only within the 0- to 10-cm soil depth and not at deeper depths. Changes in soil C concentration were larger at Garden City than at Tribune. At Garden City, the soil organic C concentration on an area basis (under the highest irrigation level) was greater than under the lowest level by 1.5 times at the 0- to 10-cm soil depth. Based on these results, soil C concentration increased at a rate of about of 6.9 kg per hectare per year for every 1 mm increase in water applied. At Tribune, differences in soil C concentration among the three irrigation levels were not statistically significant at the 0- to 5-cm soil depth. For the 5- to 10-cm depth, however, soil organic C concentration increased by 2.4 gram per kilogram of soil in 8 years as the amount of water applied increased from 127 mm to 254 mm per year. The confinement of changes in C concentration to the 0- to 10-cm depth with deficit irrigation reflects the soil organic C stratification commonly observed in no-till systems as a result of crop 4

5 residue accumulation at the soil surface. Continued application of high levels of irrigation for extended periods of time, more than 10 years, may reduce organic C stratification. Carbon balance It is important to establish a C balance between gains and losses under deficit irrigation. As indicated earlier, while higher levels of irrigation may increase C sequestration by increasing biomass C input, it also increases CO 2 emissions by increasing the amount of energy needed for pumping water over limited irrigation. Estimates indicate that CO 2 emissions from pumping water under full irrigation can be as high as 0.33 Mg C per hectare per year. If energy needed for pumping water is reduced by 70% (as an example) through deficit irrigation, the CO 2 emissions from energy use under this irrigation strategy may be only 0.10 Mg C per hectare per year, a reduction of 0.23 Mg C. It is also important to measure soil CO 2 and CH 4 emissions under deficit irrigation to accurately determine the C budget. Deficit irrigation and soil physical properties Changes in irrigation strategies had no significant effect on bulk density and particle-size distribution (data not shown) but increased the mean weight diameter of wet aggregates (Table 1). Plots receiving high amounts of irrigation water had more macroaggregates but had fewer microaggregates than plots receiving low amounts of water. Aggregate size and stability increased with the irrigation-induced increase in soil organic C concentration, particularly at Garden City. This suggests that increases in soil organic C concentration due to irrigation can improve soil structural development and reduce the soil s susceptibility to erosion. Summary Deficit irrigation had some significant effects on soil organic C concentration and wet aggregate stability near the soil surface, but had no effects on bulk density, particle-size distribution, and soil inorganic C concentration after 5 and 8 years of irrigation management. Soil organic C concentration and wet aggregate stability increased in the 0- to 10-cm soil depth with an increase in the amount of water applied. Overall, an increase in the amount of irrigation water applied increases soil C concentration and improves soil structural properties near the soil surface, but the magnitude of impacts varies with site. 5

6 Table 1. Deficit irrigation impacts on soil organic C concentration and mean weight diameter of soil aggregates for two sites in western Kansas. (Means accompanied by a lowercase letter within each column and soil depth are not significantly different.) Site Garden City Tribune Garden City Tribune Annual irrigation amount Soil depth Soil organic C Soil organic C Mean weight diameter of soil aggregates (mm) (cm) (g/kg) (Mg/ha) (mm) b 6.1b 0.9a ab 7.6ab 1.2a ab 7.1ab 1.2a 0 to ab 8.3ab 1.1a ab 7.5ab 1.0a a 8.9a 1.2a a 6.8a 0.4a to a 8.2a 0.8a a 8.6a 0.7a a 5.1b 0.7a a 5.9ab 0.7a to a 5.3ab 0.6a a 5.4ab 0.7a a 6.7ab 0.9a a 7.5a 1.0a b 5.1a 0.5b to a 6.6a 0.6ab ab 5.9a 0.9a -- Humberto Blanco, Applied Soil Physics and Soil Conservation, Agricultural Research Center - Hays hblanco@ksu.edu -- Norman L. Klocke, Irrigation Engineer, Southwest Research-Extension Center nklocke@ksu.edu -- Alan J. Schlegel, Soil Scientist, Southwest Research-Extension Center - Tribune. schlegel@ksu.edu -- Loyd R. Stone, Soil Water Management stoner@ksu.edu 6

7 3. Cover Your Acres Conference Set for Jan in Oberlin Kansas State University and the Northwest Kansas Crop Residue Alliance are teaming up to sponsor the Cover Your Acres Winter Conference Jan , 2010 in Oberlin, Kan. The conference will be at the Gateway Civic Center, starting with registration both days from 7:45 to 8:15 a.m. The program will begin at 8:20 a.m. in the Exhibit Hall. The program will be the same each day, so participants can attend the day that best fits their schedule. The fee to attend is $18 per person if paid by Jan. 12. After that date and at the door the fee is $45. The fee includes lunch, all conference proceedings, break refreshments and access to all exhibits and presentations. Participants have numerous presentations to choose from. Topics will include: * Weed control in fallow * State of fertilizer * Fertilizing for no-till * Implementing forages in no-till rotations * Plant nutrition * Micronutrients and major crops * New sunflower production strategies * Grain marketing strategies to enhance profitability * CRP conversion to crop production * Livestock risk protection * Cover crops for western Kansas * Does stacked corn pay on dryland * Long-term crop rotation results * And more Continuing education credits for 1A commercial pesticide applicators have been approved and certified crop advisor credits have been applied for. More information is available by calling , or log onto the website at -- Mary Lou Peter, News Coordinator, Department of Communications mlpeter@ksu.edu -- Brian Olson, Northwest Area Crops and Soils Specialist bolson@ksu.edu These e-updates are a regular weekly item from K-State Extension Agronomy and Steve Watson, Agronomy e-update Editor. All of the Research and Extension faculty in Agronomy will be involved as sources from time to time. If you have any questions or suggestions for topics you'd like to have us address in this weekly update, contact Steve Watson, swatson@ksu.edu, or Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader jshroyer@ksu.edu 7