March - April 2005: Volume 60, Number 2

Table of Contents

Features
Do Erosion Control and Snakes Mix?
By Christopher Barton and Karen Kinkead

The Value of Carbon Credits
By Jeffery R. Williams, Jeffrey M. Peterson, and Sian Mooney

Getting Conservation on the Land Using GIS
By Sharyl Walker and Leon Wendte

Research

Departments

• Viewpoint—Clay Ogg
• Raise Your Voice
• Notebook
• Going Retro - Celebrating 60 Years of the JSWC 
• Conservogram

No-till translanting of vegetables and tobacco to reduce erosion and nutrient surface runoff
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 2)

D.C. Yoder, T.L. Cope, J.B. Wills, and H.P. Denton
ABSTRACT: Researchers in the University of Tennessee Begetable Initiative wanted convincing proof that no-till transplanted vegetables and tobacco reduced negative environmental impacts, as has been proven for no-till seeding of other crops. This led to a two-year replicated field plot study on two soils with slopes typical of east Tennessee agriculture, planted in tomatoes or tobacco with either a no-till transplanter or a more standard tillage-based system. The runoff from the plots was collected and analyzed for sediment and nutrient content. In comparison to the tillage-based system, no-till transplanting on average reduced erosion by 92 percent and average total Kjeldahl nitrogen surface movement off of the plots by 83 percent. The no-till transplanting also reduced total phosphorus and total nitrate plus nitrite surface water runoff significantly (at a = 0.05) in two of three comparisons. Results for total runoff showed no significant trend across tillage types, soils, or crops. Finally, phosphate surface water runoff was a very small portion of total phosphorus movement but showed mized results, with significantly higher no-till system values in two of three cases. These results demonstrate that no-till transplanting can substantially reduce the overall environmental impact of specialty crop production in comparison to tillage-based systems.

Keywords: Erosion, no-till, transplanting, vegetables

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Trends in recent reservoir sediment rates in Southwestern Ohio
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 2)

W.H. Renwick, K. Carlson, and J. Hayes-Bohanan
ABSTRACT: Soil erosion rates on U.S. cropland are declining. This decline can be expected to have two effects on sediment yield: 1) an overall decrease in sediment yield; and 2) an increasing importance of channel erosion relative to upland sediment sources. Here we examine recent sedimentation rates in 12 reservoirs in two southwest Ohio counties to determine whether sedimentation rates are declining, and whether there is evidence for a shift to channel sediment sources. One of the two counties is primarily urban with high local relief, while the other is primarily agricultural with low relief. In each case a large range of reservoir sizes was studied (<1 to >70 km² drainage area or <0.39 to > 271 mi²). Previous sediment surveys are available for some of the reservoirs studied. Measured sedimentation rates range from <100 to >1200 m³ km^-2 yr^-1. Sedimentation rates are generally higher in the urban county than the agricultural one. Comparison of recent (since ~1980) sedimentation rates with those from the mid-20th Century indicate that sedimentation rates are declining in the agricultural county, presumably as a result of improved soil conservation practices, while those in the urban county remain high. In the agricultural county sedimentation rates follow the normal pattern of decreasing sedimentation per unit drainage area with increasing drainage area, indicating that the channel systems in the area are likely functioning as sediment sinks. In contrast, in the urban county there is no decrease in sedimentation rate with increasing drainage area, indicating that the channels in that landscape are functioning as efficient conduits and/or net sediment sources. These trends highlight the need to update our reservoir sedimentation datatbases to determine whether the trends are local or widespread.

Keywords: Erosion, reservoir sedimentation, sediment delivery

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Assessment of groundwater use by wheat (Triticum Aestivum L.) in the Luancheng Xian Region and potential implications for water conservation in the Northwestern North China Plain
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 2)

C. Hu, J.A. Delgado, X. Zhang, and L. Ma
ABSTRACT: Agricultural sustainability in China, especially in the North China Plain, is highly dependent on water resource availability. Land management has changed dramatically in this region since the 1970's when a more intensive practice of winter wheat (Triticum aestivum L.) and summer corn (Zea mays L.) in one-year rotation started causing excessive exploitation of groundwater to meet crop water needs for high yield productivity. Over fifth percent of the area in the northwestern region of the North China Plain is irrigated using groundwater. Over ninety percent of Luancheng Xian county is in groundwater-irrigated winter wheat - corn rotation. In addition the irrigation management practices, agricultural management practices, soil textural classes (mostly loam soils) and climate are similar throughout the Northwestern North China Plain and the Luancheng Xian county. Our objectives were to identify whether land use is a factor contributing to groundwater table decline in Luancheng Xian county of the North China PLain and to use long term small plot studies from 1998 to 2002 to evaluate the potential of limited irrigation based on wheat stage of growth as a viable water-saving practice to reduce consumptive use and stabilize the groundwater table.
      Assessment of groundwater resources for the Luancheng Xian county found that groundwater levels have been dropping at a rate of 0.8 m yr-1 (P < 0.001). This occurred during a time of significantly lower precipitation that explained about 91 percent of the groundwater depletion rate (P < 0.001). The drop in groundwater levels was also correlated (r²=0.71) with the increased area planted to wheat (P<0.001). At this current rate of groundwater use, the resource will be depleted within three decades. A more efficient management system that increases water use efficiency or amount of grain produced per unit of water use is needed for sustainability of the cropped areas. We found that irrigation scheduling based on wheat stage of growth can significantly increase water use efficiency when we target application of two key 60 mm irrigation events at the jointing and heading stages of growth when compared to traditional irrigation management practices taht use four irrigation events (240 mm) (P <0.05). Although simulated Penman-Monteith evapotranspiration from 1998 to 2002 was significantly correlated with measured values (P<0.001), Penman-Monteith evapotranspiration values were higher than evapotranspiration measure with weighing lysimeters (P < 0.05). Our 1998 to 2002 studies suggest that there is potential to use stage of growth and water budget models for irrigation scheduling in the Northwestern North China Plain and cut water use by nearly fifty percent without significantly reducing grain yields. It is imperative that these practices tested in small plots now be demonstrated in commercial applications to conserve groundwater resources and maintain agricultural sustainability needed to feed China's increasing population.

Keywords: Groundwater conservation, North China Plain, water use efficiency

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Tillage effects on rainfall partitioning and sediment yield from an ultisol in Central Alabama
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 2)

C.C. Truman, J.N. Shaw, and D.W. Reeves
ABSTRACT: Coastal Plain soils in the Southeast have been intensively cropped, traditionally managed under conventional tillage practices, and are susceptible to erosion. Conservation tillage systems have significant potential as a management tool for row crop production, expecially on sandy surface soils of the Coastal Plain because they reduce soil loss and conserve water. We quantified rainfall partitioning and sediment delievery from a Plinthic Pauleudult-Typic Hapludult soil complex (loamy sand surface) located in the in Coastal Plain region of Alabama managed under conventional- and no-till systems for 10 years. Conventional till and no-till treatments were evaluated with and without surface (Black Oat, Avena strigosa Schreb.) residue (0-9600 kg ha^-1) and with and without paratilling (non-inversion subsoiling to 40 cm). Field plots (~60 m²) represented eight treatment combinations, two tillage treatments (conventional till, no-till), two residue management treatments, residue removed or left in place (+R), and two non-inversion, deep tillage treatments, paratilled, non-paratilled, with each treatment combination replicated four times. Two 1-m² rainfall simulator plots were established on one tillage-reside-deep tillage treatment replicate. Each 1-m² plot received 2 h of simulated rainfall (50 mm h^-1). Runoff and sediment delivery were continuously measured from each flat, level-sloping 1-m² plot (slope=1 percent). No-till plots had at least two times less runoff and four times less sediment delivery compared to conventional till plots. Runoff was greatest for conventional till, residue removed, non-paratilled plots (58 percent of the rainfall amount), and lowest for no-till, residue left in place, paratilled plots (4 percent of the rainfall amount). About 42 percent of the rainfall infiltrated in the conventional till, residue removed, non-paratilled plots (worst-case scenario) compared to about 96 percent for the no-till, residue left in place, paratilled plots (best-case scenario), resulting in only 2.8 days of water for cropuse in conventiaonl till, residue removed, non-paratilled plots and 6.9 days of water for crop use in no-till, residue left in place, paratilled plots (2.5-fold difference). Removing residue resulted in 18 percent more runoff as a rainfall percentage (18 percent less infiltration) for no-till plots and 25 percent more runoff (25 percent less infiltration) for conventional till plots, and accounted for 38 to 76 percent of the differences in runoff and sediment transported from no-till and conventional till plots. For conventional till and no-till plots, removing surface residue increased sediment yield by 1.5 and 7 times. Paratilling resulted in 10 percent less runoff as a rainfall percentage (10 percent more infiltration) for no-till plots and 26 percent less runoff (26 percent more infiltration) for conventional till plots. Compared to non-paratilled conventional till and no-till plots, paratilling caused runoff rates to increase at a slower rate, and increased steady-state runoff rates by 40 percent and 400 percent, respectively. Paratilling reduced bulk density (0 to 12 cm) and soil strength 0 to 50 com) by at least 15 percent compared to non-paratilled treatments. Combining residue management and paratilling through conservation tillage in row-crop agriculture in the Coastal Plain region of Alabama reduces runoff and soil loss for conventional till and no-till systems by improving soil properties and maintaining infiltration, resulting in increased estimates of plant available water.

Keywords: Infiltration, paratill, residue, runoff, simulated rainfall, water conservation

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Grain-size variation in the Middle Yellow River attributed to soil conservation
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 2)

N. Jinren and H. Peng
ABSTRACT: The variation of suspended load resulting from human activities has been extensively investigated in rivers in China, but less is known of the corresponding variation of sediment grain size. Grain-size variation of suspended sediment with respect to regional soil conservation was analyzed using more than 20 years data (1958 to 1985) obtained from hydrologic stations distributed in the mainstem as well as in some tributaries of the Middle Yellow River. Single-factor ANOVA was used in the analusis of grain-size variations in tributaries as well as in the mainstem before and after soil conservation, and the Wilcoxon signed-rank test was used on the entire data set over the whole study area. Comparisons were made at the tributary, the regional, and the mainstem levels. It was found that sediment became finer after soil conservtion at most stations, both in the tributaries and the mainstem, though such a trend was not statistically significant at some stations. The regional comparison indicated that sediment over the whole study area became finer after soil conservation at the signifcance level of 0.05. Additional analyses were performed to evaluate the role of factors that may affect grain size variation such as rainfall, scour and deposition in channels and intrabasinal storage due to soil conservation. It was found that rainfall and scour/deposition in channels have little relation with sediment grain-size reduction in the Middle Yellow River. Intrabasinal storage caused by soil conservation was the primary factor causing grain size decreases in the study area. It was found that F-value in grain size ANOVA before and after soil conservation increased with the decrease of sediment conveyance rate after soil conservation in loess hills. That is to say, the more sediment trapped in watershed by soil conservation measures, the more significanly the grain-size became finer in rivers. However, similar relation was not found in the rivers passing both loess hills and sand-gravel hills. 

Keywords: Grain-size, sediment, soil conservation

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