January - February 2005: Volume 60, Number 1

Table of Contents

Features
When to adapt state nutrient management policies
By Charles Abdalla and Alyssa Dodd

Research

• A tool for estimating best management practice effectiveness for phosphorus pollution control
  M.W. Gitau, W.J. Gburek, and A.R. Jarrett
• Trends in phosphorus fertility of New York agricultural land
  Q.M. Ketterings, J.E. Kahabka, and W.S. Reid
• Evaluation of some phosphorus index criteria in cultivated agriculture in clay soil
  H.A. Torbert, R.D. Harmel, K.N. Potter, and M. Dozier
• Field evaluation of three phosphorus indices on new application sites in Texas
  R. D. Harmel, H.A. Torbert, P.B. DeLaune, B.E. Haggard, and R.L. Haney
• Soil organic carbon variability and sampling optimization in Montana dryland wheat fields
  R.S. Bricklemyer, P.R. Miller, K. Paustian, T. Keck, G.A. Nielsen, and J.M. Antle 
• Mapping surface soil organic carbon for crop fields with remote sensing
  F. Chen, D.E. Kissel, L.T. West, D. Rickman, J.C. Luvall, and W. Adkins
• Influence of summer cover crops on conservation of soil water and nutrients in a subtropical area
  Q. Wang, Y. Li, and W. Klassen 
• Effectiveness of sand mulch in soil and water conservation in an arid region, Lanzarote, Canary Islands, Spain
  C.C. Jimenez, M. Tejedor, F. Diaz, and C.M. Rodriguez

Departments

• Homefront
• Viewpoint—Max Schnepf 
• Raise Your Voice
• Notebook
• Going Retro - Celebrating 60 Years of the JSWC 
• Conservogram

A tool for estimating best management practice effectiveness for phosphorus pollution control 
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

M.W. Gitau, W.J. Gburek, and A.R. Jarrett
ABSTRACT: A best management practice (BMP) tool was developed as a part of an effort to address the phosphorus (P) pollution and associated eutrophication problem affecting the Cannonsville Reservoir, part of the New York City water supply system. P reaching the reservoir is thought to emanate from runoff from the surrounding farms, mainly as a result of manure spread on these farms. Efforts to address the problem have involved implementation of BMPs on the watersheds; however, the effectiveness of these practices is not known. This study establishes a means of estimating BMP effectiveness, based on data available in the literature, and develops a tool that allows users to obtain BMP effectiveness estimates for their respective site soil and slope conditions. The tool offers stand-alone capabilities and has the potential to be linked to a GIS. An example is presented to illustrate tool application for effectiveness-based BMP selection, with a focus on a farm within the New York City watersheds.

Keywords: Best management practice (BMP) effectiveness, BMP tool, cumulation, analyses

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Trends in phosphorus fertility of New York agricultural land
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

Q.M. Ketterings, J.E. Kahabka, and W.S. Reid
ABSTRACT: Monitoring of soil test phosphorus (STP) levels over time is essential for the evaluation of fertility management practices. Our objectives were to (1) assess the current soil P fertility status of New York at state, regional, county, and farm level, (2) determine statewide and regional trends over the past 40 years, and (3) investigate the impact of soil test phosphorus trends on fertilizer needs for typical corn-alfalfa/grass rotations. A 1995 to 2001 dataset (119,326 soil samples analyzed for Morgan extractable P) from the Cornell Nutrient Analysis Laboratory was analyzed and compared with published data from 1957-58, 1977-78, 1981, and 1982, and unpublished data from 1985 to 95. Mean statewide P levels remained constant from 1957 to 1980 (26 to 29 percent high or very high in P), but steadily increased after 1980. Currently, 47 percent of the soil samples test equal to or higher than the critical agronomic soil test phosphorus for field crops (4.5 mg kg^-1 or 9 lbs ac^-1 Morgan extractable P). The highest soil test levels occur in vegetable production regions on Long Island and the highly productive dairy, vegetable and fruit areas in Western New York while the greatest increases over time took place in the dairy-dominated northern and northeastern regions. As these soils reach progressively higher P levels, fertilizer P needs for New York will diminish but more attentive management is needed to ensure that environmental thresholds are not exceeded.

Keywords: Morgan's solution, New York, phosphorus soil tests, soil fertility

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Evaluation of some phosphorus index criteria in cultivated agriculture in clay soil
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

H.A. Torbert, R.D. Harmel, K.N. Potter, M. Dozier
ABSTRACT: There are growing concerns regarding the fate of nutrients from land application of animal waste. In recent years, phosphorus (P) indices have been developed to provide information regarding nutrient loss potentials from animal waste application methods and topography. However, in many cases, these P indices have not been fullly tested, especially in cultivated agriculture. Three factors commonly utilized in soil P indices for manure management are manure rate, manure incorporation, and slope. Rainfall simulations were conducted to examine the impact of these three factors on runoff losses of P on heavy clay soils under cultivated agriculture. Four manure litter (turkey litter) application rates (0, 4.5, 9.0, and 13.5 Mg ha^-1 (0, 2, 4, and 6 ton ac^-1)) were applied on two different slopes (5 and 9 percent) on a Heiden clay (fine, montmorillonithic, thermic Udic Chrosmusterts). The litter was surface applied to a corn (Zea mays L.) production area, with or without incorporation. The four application rates were also applied to a permanent Bermuda grass (Cynodon dactylon (L.) Pers.) pasture on a 5 percent slope. A rainfall simulator was used to generate water runoff for 30 minutes from 1.5 by 2.0 m (5 by 6.5 ft) plots. Runoff samples were analyzed for runoff volume, sediment, sediment nitrogen (N) and P, dissolved ammonia nitrogen (NH₄-N), nitrate nitrogen (NO₃-N), and PO₄-P. The results were analyzed for using regression analysis techniques based on application rates. The dissolved NO₃-N concentration was not affected by either litter incorporation or slope in the cultivated sites, but was greatly increased with increasing litter application rate in the pasture sites. Increased losses of dissolved NG₄-N and PO₄-P were observed with increasing litter application rate, with a significant reduction in losses observed when litter was incorporated. However, increased slope did not significantly impact the level of runoff losses of dissolve NG₄-N and PO₄-P.

Keywords: Manure management, phosphorus, rainfall simulation, surface runoff, water quality

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Field evaluation of three phosphorus indices on new application sites in Texas
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

R.D. Harmel, H.A. Torbert, P.B. DeLaune, B.E. Haggard, R. Haney
ABSTRACT: Phosphorus (P) indices were developed to address nonpoint source P losses from agricultural fields; however, only limited information on P index performance at the field- and watershed-scale is available. Evaluation of P indices is necessary to provide the basis of modification and improvement of their usefulness as P management tools. In this study, the ability of the Texas P index to estimate P loss potential was evaluated by comparison with measured annual P loads over three years on four new pasture and six new cultivated litter application sites in the Texas Blackland Prairie. The Arkansas and Iowa P indices were also evaluated. The Texas and Iowa versions were able to provide reasonable estimates of P loss potential as illustrated with significant linear relationships (p < 0.01) between P index values and measured annual P loads. In general, the P index values, Mehlich 3 soil test P, and poultry litter application rate were better correlated with dissolved P concentrations and loads (r² ranged from 0.12 to 0.91) than with total P and particulate P loads (r² ranged from 0.00-0.31). A major source of error in P index load estimations was their inability to capture variability in annual soil erosion. This source of error was dramatically reduced by using measured erosion instead of estimated annual average erosion (average r² values increased from 0.24 to 0.58). While these results illustrate a potential for the P Indices to make relative P loss assessments, research on incentives to prevent buildup of soil P levels, linkages between P levels in soils and receiving waters, and other important issues related to the use of P indices is warranted.

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Soil organic carbon variability and sampling optimization in Montana dryland wheat fields
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

R.S. Bricklemyer, P.R. Miller, K. Paustian, T. Keck, G.A. Nielsen, and J.M. Antle
ABSTRACT: Soil organic carbon varies spatially as a function of short-range and landscape scale variability and is influenced by natural soil variability, soil management, and variability associated with soil sampling techniques. Accurate measurement methods and efficient smapling designs are needed to determine the net carbon change over time as a function of soil managment changes. Soil organic carbon sampling variability in paired no-till and tilled dryland wheat fields in Montana was examined. Paired fields at two locations were chosen with soils, cropping system, landscape position, and climatic conditions similar within each pair. Sampling variability in soil organic carbon for the 0 to 10 cm depth was quantified among cores, microsites, and fields. Soil samples were analyzed for total and inorganic C, and particle-size distribution. Stratifying by soil-landscape association likely reduced soil organic carbon sample variability. Including percent clay as a covariant reduced soil organic carbon variance 40-fold (site level), however variance within sites (tillage effect) remained unchanged. Soil organic carbon was greater in no-till fields than tilled fields (P<0.01) at both Ft. Benton (18.2 Mg C ha^-1 and 14.4 Mg C ha^-1, respectively) and Simpson (8.8 Mg C ha^-1 and 6.9 Mg C ha^-1, respectively). Variability within and between microsites was used to optimize the number of microsites per field and the number of cores per microsite for reliable soil organic carbon measurements. An optimal sampling design for four microsites by two cores or three microsites by three cores provided reliable detection of a tillage effect on soil organic carbon in fields sampled.

Keywords: Carbon sequestration, no-till, sampling optimization, sampling variability, soil-landscape association, soil organic carbon

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Mapping surface soil organic carbon for crop fields with remote sensing
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

F. Chen, D.E. Kissel, L.T. West, D. Rickman, J.C. Luvall, and W. Adkins
ABSTRACT: The soil organic carbon (C) concentration of surface soil can be used in agricultural fields to vary crop production inputs. Soil organic C is often highly spatially variable, so that maps of soil organic carbon can be used to vary crop production inputs using precision farming technology. The objective of this research was to demonstrate the feasibility of mapping soil organic carbon on three fields, using remotely sensed images of the fields with a bare surface. Soil samples covering the range in soil organic carbon were taken from each field to develop a satisfactory relationship between soil organic carbon content and image reflectance values. The regression equations differed between fields, but gave highly significant relationships with R² values of 0.93, 0.95, and 0.89 for the three fields. Two classification, arbitrarily classification and a minimum distance clustering, were applied in mapping soil organic carbon. A comparison of mapped soil organic carbon with an independent set of 21 soil samples taken on one of the fields gave highly satisfactory results for the two methods with r² = 0.81 and 0.87.

Keywords: Field variation, global positioning systems, image filtering, mapping, remote sensing, soil organic carbon

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Influence of summer cover crops on conservation of soil water and nutrients in a subtropical area
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

Q. Wang, Y. Li, and W. Klassen
ABSTRACT: To elucidate the effects of summer cover crops on vegetable production, on soil water conservation and on reducing nutrient leaching from the soil, a pot experiment was conducted on Krome soil with legume and non-legume cover crops. Natural weedy fallow served as the control. The cover crops were sunn hemp (Crotalaria juncea L.) cowpea (Vigna unguiculata (L. Walp)), velvetbean (Mucuna deeringiana (Bort.) Merr.), and sorghum sundangrass (Sorghum bicolor x S. bicolor var. sudanense (Piper) Stapf). The leachate from under each pot was collected weekly, measured, and analyzed for concentrations of nitrate (NO₃-N), ammonium (NH₄-N) and inorganic phosphorus (P). The results showed that compared to the control, legume cover crops, especially sunn hemp, significantly improved tomato yields, and all the cover crops significantly reduced water and nutrient leaching. The amounts of NO₃-N in the leachates collected during six-week period from pots with cover crops was equivalent to 0.9 to 2.2 kg ha^-1, which was significantly less than 16.1 kg ha^-1 from the weedy fallow (control). In the fallow treatment, 21.3 percent of fertilizer nitrogen (N) was lost through leaching, but only 1.3 to 3.2 percent was lost with cover crops. Taking account of plant uptake and leaching, total amounts of 26.9 and 40.6 kg N ha^-1 were lost from the soil pool for the treatments in fallow and sorghum sudangrass but 28 to 252.7 kg N ha^-1 were obtained mostly by N fixation via rhizobia and accumlated in leguminous cover crops. Although relative amounts of fertilizer P lost via leaching were meager for all the treatments, at least twice as much was lost from fallow (0.4 percent) rather than from treatments with cover crops (0.1 to 0.2 percent). Compared to the control (fallow with weeds), velvetbean and sunn hemp reduced inorganic P losses by 70 percent and 66 percent, while cowpea and sorghum sudangrass reduced losses by only 19 percent and 13 percent. Leguminous cover crops reduced leachate volume by 55 percent to 91 percent, sorghum sudangrass reduced leachate by 61 percent, while fallow soil with natural weeds only reduced leachate by 48 percent of applied water. The results suggest that summer leguminous cover crops can not only prevent the loss through leaching of 88 to 94 percent of soil N and of 50-83 percent of inorganic P but also accumulated 2.0 to 8.7 fold more N in the plants, which contribute to improving the subsequent vegetable yield after returned to the soil.

Keywords: Cover crops, inorganic P, leachate, leaching, legume, NH₄-N, non-legume, NO₃-N

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Effectiveness of sand mulch in soil and water conservation in an arid region, Lanzarote, Canary Islands, Spain 
(Full text appears in the Journal of Soil and Water Conservation, Vol.60, No. 1)

C.C. Jimenez, M. Tejedor, F. Diaz, and C.M. Rodriguez
ABSTRACT: The arid climate of some zones of the Canary Islands (Spain) requires the use of traditional farming practices for soil and water conservation, including the use of sand mulch. Results from field studies and laboratory experiments showed that soil moisture loss due to Cevaporation in mulched soils was reduced by 76 percent and the water content was higher (1.6:1) when compared to uncovered soils. The modification produced in the soil moisture regime - udic under mulch and aridic without covering affects the classification of the soils, as Inceptisols in the first case and Aridisols in the second. This research confirmed the effectiveness of the sand mulch as a conservation practice. The results showed that watermelons, melons and sweet potatoes can be grown without irrigation in the mulched soils, but not in soils without cover.

Keywords: Arid soils, Canary Islands, dry farming, mulching, soil moisture regime, water conservation