Deep Loess Soils Research Articles

Modelling the artificial forest (<i>Robinia pseudoacacia</i> L.) root–soil water interactions in the Loess Plateau, China

Abstract. Plant root–soil water interactions are fundamental to vegetation–water relationships. Soil water availability and distribution impact the temporal–spatial dynamics of roots and vice versa. In the Loess Plateau (LP) of China, where semi-arid and arid climates prevail and deep loess soil dominates, drying soil layers (DSLs) have been extensively reported in artificial forestland. While the underlying mechanisms that cause DSLs remain unclear, they hypothetically involve root–soil water interactions. Although available root growth models are weak with respect to simulating the rooting depth, this study addresses the hypothesis of the involvement of root–soil water interactions in DSLs using a root growth model that simulates both the dynamic rooting depth and fine-root distribution, coupled with soil water, based on cost–benefit optimization. Evaluation of field data from an artificial black locust (Robinia pseudoacacia L.) forest site in the southern LP positively proves the model's performance. Further, a long-term simulation, forced by a 50-year climatic data series with varying precipitation, was performed to examine the DSLs. The results demonstrate that incorporating the dynamic rooting depth into the current root growth models is necessary to reproduce soil drying processes. The simulations revealed that the upper boundary of the DSLs fluctuates strongly with infiltration events, whereas the lower boundary extends successively with increasing rooting depth. Most infiltration was intercepted by the top 2.0 m layer, which was the most active zone of infiltration and root water uptake. Below this, the percentages of fine roots (5.0 %) and water uptake (6.2 %) were small but caused a persistently negative water balance and consequent DSLs. Therefore, the proposed root–water interaction approach succeeded in revealing the intrinsic properties of DSLs; their persistent extension and the lack of an opportunity for recovery from the drying state may adversely affect the implementation of artificial afforestation in this region as well as in other regions with similar climates and soils.

An approach to identifying and evaluating the potential formation of ephemeral gullies in the conditions of the Czech Republic

Soil erosion, including ephemeral gully erosion, is a serious degradation process in the Czech Republic. It currently threatens more than half of the agricultural acreage through negative changes in the whole complex of soil properties. The unfavourable consequences of surface runoff are seen in the erosion processes degrading agricultural soils. The South Moravia Region was selected as the case study area – mainly for its natural conditions and high soil degradation risk . A set of data, collected from 2012 to 2017 in a maize-growing area, especially on deep loess soils in the South Moravia Region, was used to analyse the morphological characteristics of the ephemeral gullies (EGs). The relationship was confirmed between the ephemeral gully (EG) length and the size of its contributing drainage area in accordance with studies conducted in other countries. It is also important that the closest relationship was confirmed between the length of the gully and its calculated volume. Dependence was sought on the data of 51 cases of the detailed, measured and evaluated EGs. These results will become the basis for finding a predictive relationship and the quantification of EG erosion. Locating EGs and predicting their length is crucial for estimating the sediment load and planning conservation strategies. The aim of this paper is to contribute to the understanding of this issue, i.e., define and verify the basic crucial causal factors and propose guidelines for locating the potential EG occurrence and predicting the sediment load. A research effort to better understand the EG mechanism and causal factors over a wide range of watershed conditions is fundamental to the establishment of basic rules for the adoption of optimal conservation strategies.

Different microbial responses in top‐ and sub‐soils to elevated temperature and substrate addition in a semiarid grassland on the Loess Plateau

The Loess Plateau soil in northwest China originated from wind sediments and is characterized by deep soil profiles and large organic carbon (C) content. Severe soil erosion constantly exposes deep soils to the surface, making the organic C vulnerable to microbial decomposition. Few, however, have so far examined how soil microbial activity and community composition in the deep loess soil respond to perturbations. We examined microbial responses in three layers of a clay‐loam loess (topsoil, 0–20 cm; midsoil, 40–60 cm; subsoil, 80–100 cm) to substrate additions (0.8 g glucose‐C kg−1 soil) under two temperature regimes (25 and 35°C). Soil C:N ratio was significantly larger in the subsoil (20.3) than topsoil (7.4). Glucose addition significantly increased CO2 efflux during a 30‐day incubation period and the relative magnitude of the increase was four times larger in the subsoil than topsoil. The temperature sensitivity (Q10) of soil CO2 efflux increased significantly with soil depth in the absence of glucose addition (i.e., ambient soil), but it decreased under glucose addition. Also, glucose addition significantly increased phenol oxidase and peroxidase activities in the subsoil, which might contribute to the stimulation of microbial CO2 efflux. Composition of the microbial community was more affected by temperature increase in the topsoil, but more responsive to labile C addition in the subsoil. Together, these results indicated that the composition of soil communities and microbial activities in the topsoil and deep soil responded differently to warming and labile C input. Our findings suggest that organic C in deep loess soils can be highly sensitive to environmental changes, emphasizing the need for more long‐term monitoring and quantitative assessment of organic C release from this important C pool.Highlights Microbial responses to labile C and warming were examined along a Loess Plateau soil profile. Microbial respiration was more responsive to C addition and warming in deep soil than topsoil. Microbial composition and activity were sensitive to temperature in the topsoil but to labile C in the subsoil. Climate change may facilitate CO2 efflux from deep Loess Plateau soils.

How Well Does Noah-MP Simulate the Regional Mean and Spatial Variability of Topsoil Water Content in Two Agricultural Landscapes in Southwest Germany?

Abstract The spatial variability of topsoil water content (SWC) is often expressed through the relationship between its spatial mean 〈θ〉 and standard deviation σθ. The present study tests the concept that a reasonably performing land surface model (LSM) should be able to produce σθ–〈θ〉 data pairs that fall into a polygon, spanned by the cloud of observed data and two anchor points: σθ at the permanent wilting point σθ–〈θwp〉 and σθ at saturation σθ–〈θs〉. A state-of-the-art LSM, Noah-MP, was driven by atmospheric forcing data obtained from eddy covariance field measurements in two regions of southwestern Germany, Kraichgau (KR) and Swabian Alb (SA). KR is characterized with deep loess soils, whereas the soils in SA are shallow, clayey, and stony. The simulations series were compared with SWC data from soil moisture networks operating in the two study regions. The results demonstrate that Noah-MP matches temporal 〈θ〉 dynamics fairly well in KR, but performs poorly in SA. The best match is achieved with the van Genuchten–Mualem representation of soil hydraulic functions and site-specific rainfall, soil texture, green vegetation fraction (GVF) and leaf area index (LAI) input data. Nevertheless, most of the simulated σθ–〈θ〉 pairs are located outside the envelope of measurements and below the lower bound, which shows that the model smooths spatial SWC variability. This can be mainly attributed to missing topography and terrain information and inadequate representation of spatial variability of soil texture and hydraulic parameters, as well as the model assumption of a uniform root distribution.

Variations of Soil Organic Carbon Following Land Use Change on Deep‐Loess Hillsopes in China

AbstractLand use change is a key factor driving changes in soil organic carbon (SOC) around the world. However, the changes in SOC following land use changes have not been fully elucidated, especially for deep soils (>100 cm). Thus, we investigated the variations of SOC under different land uses (cropland, jujube orchard, 7‐year‐old grassland and 30‐year‐old grassland) on hillslopes in the Yuanzegou watershed of the Loess Plateau in China based on soil datasets related to soils within the 0–100 cm. Furthermore, we quantified the contribution of deep‐layer SOC (200–1,800 cm) to that of whole soil profiles based on soil datasets within the 0–1,800 cm. The results showed that in shallow profiles (0–100 cm), land uses significantly (p < 0·05) influenced the distribution of SOC contents and stocks in surface layer (0–20 cm) but not subsurface layers (20–100 cm). Pearson correlation analysis indicated that soil texture fractions and totalNwere significantly (p < 0·05 or 0·01) correlated with SOC content, which may have masked effects of land use change on SOC. In deep profiles (0–1,800 cm), SOC stock generally decreased with soil depth. But deep soils showed high SOC sequestration capacity. The SOC accumulated in the 100–1,800 m equalled 90·6%, 91·6%, 87·5% and 88·6% of amounts in the top 100 cm under cropland, 7‐year‐old grassland, 30‐year‐old grassland and jujube orchard, respectively. The results provide insights into SOC dynamics following land use changes and stressed the importance of deep‐layer SOC in estimating SOC inventory in deep loess soils. Copyright © 2017 John Wiley & Sons, Ltd.

Field Performance of <i>Quercus bicolor</i> Established as Repeatedly Air-Root-Pruned Container and Bareroot Planting Stock

Benefits of repeated air-root-pruning of seedlings when stepping up to progressively larger containers include excellent lateral root distribution immediately below the root collar and an exceptionally fibrous root ball. To evaluate long-term field performance of repeatedly air-root-pruned container stock, three plantings of swamp white oak (Quercus bicolor Willd.) 10 to 13 years old were located that also included bareroot planting stock. Initial and final stem diameter and height and above-ground green weights were determined on randomly selected trees at each site. On a site with a sandy, excessively drained, high pH soil, trees (age 10) from container stock were 1.5 times taller, 2.3 times larger in dbh, and 2.8 times greater in green weight than trees from bareroot stock which averaged only 2.9 m tall, 3.9 cm dbh, and 16.3 kg green weight. On a site with high clay, poor internal drainage, and frequent flooding, trees (age 12) from container stock were 1.4 times taller, 1.8 times larger in dbh, and 4.1 times greater in green weight than trees from bareroot stock which averaged 4 m tall, 7.3 cm dbh, and 28 kg green weight. On an upland site with deep loess soils, there was a trend for trees (age 13) from container stock to be only slightly larger than trees from bareroot stock with each stock type averaging 9.6 m tall, 20 cm dbh, and 177 kg green weight. Repeated air-root pruning produced lateral roots immediately below the root collar that resulted in large container stock with large well-balanced root systems that were competitive on harsh or less than ideal oak sites. Although the process is relatively labor intensive, propagation of repeatedly air-root-pruned container stock is readily adaptable internationally to locally available sources of organic matter and open-bottom containers.

Soil quality in a pecan–kura clover alley cropping system in the Midwestern USA

Intercropping alleys in agroforestry provides an income source until the tree crop produces harvestable yields. However, cultivation of annual crops decreases soil organic matter and increases soil erosion potential, especially on sloping landscapes. Perennial crops maintain a continuous soil cover, increase water infiltration, reduce soil erosion, and improve overall soil quality. The objective of this on-farm study was to assess the effects of a perennial legume, kura clover (Trifolium ambiguum M. Bieb.), on soil quality in a recently established pecan (Carya illinoinensis Wangenh. C. Koch) orchard. The pecan-kura clover agroforestry practice was established on deep loess soils of the Missouri River hills landscape. These silt loams are on 2–20% slopes and can be highly erosive. Kura clover, introduced as the alley crop 5 years after pecan planting, was selected based on its perennial growth habit, nitrogen-fixing ability, winter hardiness, high forage quality, and soil conservation properties. Kura clover was seeded in 2001 and harvested for hay annually beginning 2003. Soil quality indicators of total organic C, total N, water-stable aggregates, and selected soil enzymes were determined on surface soil samples collected annually after kura clover establishment. Soil organic C and activities of soil enzymes increased compared with cultivated and grass pasture control soils by the eighth year of establishment. Water-stable aggregation improved by 50% and surface soil shear strength improved significantly (P < 0.05) in alleys compared with control sites. Results illustrate that kura clover as the alley-cropped component improved soil fertility and biological activity through increased organic matter and improved soil structure, and yielded high quality forage valuable for the cattle-feeding operation. Kura clover maintained or improved soil quality, reduced soil erosion potential, and benefited pecan growth by providing a source of soil nitrogen and improving soil structure for adequate water infiltration and aeration.

Soil moisture of different vegetation types on the Loess Plateau

Water stored in deep loess soil is one of the most important resources regulating vegetation growth in the semi-arid area of the Loess Plateau, but planted shrub and forest often disrupt the natural water cycle and in turn influence plant growth. The purpose of this study was to examine the effects of main vegetation types on soil moisture and its inter-annual change. Soil moisture in 0–10 m depth of six vegetation types, i.e., crop, grass, planted shrub of caragana, planted forests of arborvitae, pine and the mixture of pine and arborvitae were measured in 2001, 2005 and 2006. Soil moisture in about 0–3 m of cropland and about 0–2 m of other vegetation types varied inter-annually dependent on annual precipitation, but was stable inter-annually below these depths. In 0–2 m, soil moisture of cropland was significantly greater than those of all other vegetation types, and there were no significant differences among other vegetation types. In 2–10 m, there was no significant moisture difference between cropland and grassland, but the soil moistures under both of them were significantly higher than those of planted shrub and forests. The planted shrub and forests had depleted soil moisture below 2 m to or near permanent wilting point, and there were no significant moisture differences among forest types. The soil moisture of caragana shrub was significantly lower than those of forests, but the absolute difference was very small. The results of this study implicated that the planted shrub and forests had depleted deep soil moisture to the lowest limits to which they could extract and they lived mainly on present year precipitation for transpiration.

Within-field nitrogen response in corn related to aerial photograph color

Precise management of nitrogen (N) using canopy color in aerial imagery of corn (Zea mays L.) has been proposed as a strategy on which to base the rate of N fertilizer. The objective of this study was to evaluate the relationship between canopy color and yield response to N at the field scale. Six N response trials were conducted in 2000 and 2001 in fields with alluvial, claypan and deep loess soil types. Aerial images were taken with a 35-mm slide film from ≥1100 m at the mid- and late-vegetative corn growth stages and processed to extract green and red digital values. Color values of the control N (0 kg N ha−1) and sufficient N (280 kg N ha−1 applied at planting) treatments were used to calculate the relative ratio of unfertilized to fertilized and relative difference color values. Other N fertilizer treatments included side-dressed applications in increments of 56 kg N ha−1. The economic optimal N rate was weakly related (R2 ≤ 0.34) or not related to the color indices at both growth stages. For many sites, delta yield (the increase in yield between control N and sufficient N treatments) was related to the color indices (R2 ≤ 0.67) at the late vegetative growth stage; the best relationship was with green relative difference. The results indicate the potential for color indices from aerial photographs to be used for predicting delta yield from which a site-specific N rate could be determined.

Environmental and economic potential of Bedouin dryland agriculture

PurposeThe purpose of the paper is to show that land degradation and desertification are threatening the livelihood of more than a billion dryland inhabitants. The paper aims to present traditional and novel approaches for sustainable agricultural exploitation of the arid drylands in Southern Israel and similar climatic zones, and their potential for rehabilitating degraded drylands and increasing agricultural productivity.Design/methodology/approachThe paper analyses the current agricultural activities on the Abu Rabia farm as well as developing experimental approaches and discusses the expected impact on ecological, economic and social sustainability.FindingsThe farm investigated consists of about 120 hectares of semi‐desert land 30 km east of Beer Sheva, divided about 50:50 between rocky hill country and plains with deep loess soil. The area receives an average 200 mm of rain per year. The land is used for raising livestock (about 120 head of sheep and goats), wheat cultivation on high quality soil, and agroforestry, mainly olive cultivation in terraces designed to collect runoff water of seasonal streams. These activities provide a basic income and cover a significant amount of the families' food requirements, but can not provide a full income for a family head in a developed country like Israel. Improving the quality of the grazing land by silvipasture, further investments into high value dryland tree crops and simultaneous production of wood for industry and energy can dramatically increase the farm's income, its resilience to drought and ecological sustainability.Practical implicationsThis analysis demonstrates the potential of dryland agroforestry for sustainable development while solving a number of economic and social problems of poor dryland inhabitants, and it contributes to fighting desertification and global warming.Originality/valueThis case study demonstrates that sustainable dryland exploitation by agroforestry can establish significant agricultural production potentials on marginal lands often considered worthless. Because of the establishment of significant and permanent carbon sinks, carbon trading may be mobilized to cover the required investments creating a classical win‐win situation.

Bulk density as a soil quality indicator during conversion to no-tillage

Producers often identify compaction as an important problem, so bulk density is usually included in minimum data sets used to evaluate tillage and crop management effects on soil quality. The hypothesis for this study was that bulk density and associated water content would be useful soil quality indicators for evaluating the transitional effects associated with changing tillage and crop management practices on deep-loess soils. The study was conducted on three deep-loess, field-scale watersheds located in western Iowa, USA. The soils are classified as Haplic Phaeozems, Cumulic-Haplic Phaeozems, and Calcaric Regosols. Watersheds 1 and 2 were converted in 1996 from conventional tillage to no-tillage, while watershed 3 was maintained using ridge-tillage and continuous corn ( Zea mays L.), a practice implemented in 1972. Watershed 1 was converted to a corn—soybean ( Glycine max (L.) Merr.) rotation while watershed 2 was converted to a 6-year rotation that included corn, soybean, corn plus 3 years of alfalfa ( Medicago sativa L.). Bulk density and water content were measured at three landscape positions (summit, side-slope, and toe-slope), in 20 mm increments to a depth of 300 mm, five times between September 1996 and May 2000. Organic C and total N were also measured to a depth of 160 mm during the initial sampling. Neither bulk density nor water content showed any significant differences between the two watersheds being converted to no-tillage or between them and the ridge-till watershed. There also were no significant differences among landscape positions. Bulk densities and water contents showed some differences when adjacent sampling dates were compared, but there was no overall or consistent trend. Our results show that bulk density is not a useful soil quality indicator for these soils within the bulk density range encountered (0.8–1.6 Mg m 3). Our results also confirm that producers do not necessarily have to worry about increased compaction when using ridge-tillage or changing from conventional to no-tillage practices on these or similar deep-loess soils.

Fate and movement of atrazine, cyanazine, metolachlor and selected degradation products in water resources of the deep Loess Hills of Southwestern Iowa, USA.

The environmental fate and movement of herbicides widely used for weed control in corn are assessed for a deep loess soil in southwestern Iowa. Beginning in the early 1980s, the herbicide-based weed control program emphasized the application of atrazine (ATR) or cyanazine (CYN) and metolachlor (MET) for both broadleaf and grass control. Between 1992 and 1995, concentrations of ATR, desethylatrazine (DEA), desisopropylatrazine (DIA), CYN and MET were measured in rainwater, both shallow and deep vadose zone water, and well water. Results show that the frequency of herbicide detections and the range and distribution of occurrences are dependent upon both landscape position and temporal inputs of recharge water from rainfall. Generally, DIA was observed more frequently and in higher mean concentration in well water than DEA, while DEA was observed more frequently than DIA in vadose zone groundwater. A chromatographic analogy is suggested to explain the occurrence patterns observed for both parent herbicide and degradation products within the unsaturated zone water. Analysis of rainwater samples collected during this time also revealed low concentrations of ATR, CYN and MET, with the timing of the detections indicative of non-local transport. Results show that the deep loess soil conducts both water and agricultural chemicals relatively rapidly and as such represents a production system which is vulnerable to contamination of shallow groundwater by herbicide-derived chemicals. Results also illustrate the importance of including major herbicide degradation products in water resource impact assessment studies.

Validation of EPIC for Two Watersheds in Southwest Iowa

AbstractThe Erosion Productivity Impact Calculator (EPIC) model was validated using long‐term data collected for two southwest Iowa watersheds in the Deep Loess Soil Region, which have been cropped in continuous corn (Zea mays L.) under two different tillage systems (conventional tillage vs. ridge‐till). The annual hydrologic balance was calibrated for both watersheds during 1988 to 1994 by adjusting the runoff curve numbers and residue effects on soil evaporation. Model validation was performed for 1976 to 1987, using both summary statistics (means or medians) and parametric and nonparametric statistical tests. The errors between the 12‐yr predicted and observed means or medians were &lt;10% for nearly all of the hydrologic and environmental indicators, with the major exception of a nearly 44% overprediction of the N surface runoff loss for Watershed 2. The predicted N leaching rates, N losses in surface runoff, and sediment loss for the two watersheds clearly showed that EPIC was able to simulate the long‐term impacts of tillage and residue cover on these processes. However, the results also revealed weaknesses in the model's ability to replicate year‐to‐year variability, with r2 values generally &lt;50% and relatively weak goodness‐of‐fit statistics for some processes. This was due in part to simulating the watersheds in a homogeneous manner, which ignored complexities such as slope variation. Overall, the results show that EPIC was able to replicate the long‐term relative differences between the two tillage systems and that the model is a useful tool for simulating different tillage systems in the region.

Field‐Scale Nitrogen Balances Associated with Long‐Term Continuous Corn Production

AbstractExcessive residual soil NO3‐N indicates economic inefficiency for producers and increases the potential for nonpoint leaching of N to water resources. Our objective was to construct an approximate fieldscale N budget for continuous corn (Zea mays L.) grown on deep loess soils in four 30‐ to 60‐ha field‐scale watersheds in western Iowa. Preplant and postemergence soil NO3‐N levels were determined for the 0‐ to 30‐cm, 30‐ to 60‐cm, and 60‐ to 90‐cm depths in April before N fertilizer was applied and again at the V6 growth stage. A simple root‐zone water balance and N removal by corn grain were determined. The 4‐yr average showed approximately 100 kg ha−1 of NO3‐N in the upper 90 cm of the root zone before an average of 168 kg of fertilizer N ha−1 was applied. Grain removal accounted for 30 to 70% of the fertilizer N. There were significant differences in grain yield and N removal among the four watersheds. Factors contributing to those differences included different fertilizer rates, tillage practices, and application times. During the four study years, an average of 50% of the applied N was available for leaching, denitrification, and/ or NH3 volatilization. High levels of residual soil NO3‐N following continuous corn production coupled with steady percolation of precipitation that infiltrated but was not used by the corn crop appear to be the two major factors supplying NO3‐N to groundwater baseflow that enters streams draining the watersheds. Based on the seasonal water balance, the most successful N management strategies will be those that minimize the amount of residual NO3‐N remaining in the soil profile at the end of the growing season.

Non-biomass soil organic N — the substrate for N mineralization flushes following soil drying–rewetting and for organic N rendered CaCl 2-extractable upon soil drying

Soil drying enhances the amount of organic N (N org) extracted by chemical methods and used as N availability indices and renders some N org mineralizable. My aim was to define the sources of these N flushes and to evaluate the relevance of soil drying–rewetting as a driving force for N mineralization. The results of three laboratory experiments, supplemented by a field study, are presented. The N org extracted by CaCl 2 after drying (40°C) originated predominately from a non-biomass soil organic N-pool. The same source of substrate was found to become mineralizable by soil drying and rewetting. There was a significant relationship between the N org extracted from dried soil samples and the magnitude of N mineralization flushes following soil drying–rewetting ( r 2=0.861***). No such correlation was found with total soil N. These results suggest that the substrate rendered extractable and that becoming mineralizable were derived mainly from the same source. A field study showed that deep loess soils under the moderate climate of central Europe did not dry out sufficiently, even in the upper 2 cm of soil during the hot summer period, to render a substantial amount of N org extractable. The possibility is discussed that the N org rendered extractable upon soil drying may represent a part of a labile non-biomass soil organic N-pool and thus may provide an N availability index, even for soils under continuously moist conditions.

Estimates of future impacts of degrading streams in the deep loess soil region of western Iowa on private and public infrastructure costs

In the beginning of the 20th century, many streams in western Iowa were channelized to reduce flooding and to open swamp land to cultivation. Channel straightening accomplished its goal. However, it resulted in greater streamflow velocities, causing stream channels to degrade. This degradation has resulted in significant loss of land and damage to transportation and communications infrastructure in western Iowa and in several states in the United States. Baumel et al. (1994; Impact of Degrading Western Iowa Streams on Private and Public Infrastructure Costs. Final Report Iowa DOT HR-352, Stream Stabilization in Western Iowa) estimated the historical cost of this degradation on land loss and damage to transportation and communications infrastructure in western Iowa. The purpose of this paper is to extend the Baumel et al. analysis to estimate future degradation costs on 141 streams in western Iowa. It also presents two types of degradation cost estimates. One is a time neutral cost that does not consider the dates on which the degradation costs are incurred. The second is a time value cost which considers the dates on which the costs are incurred and then discounts these costs back to 1992 dollars. The time value costs are the more accurate estimates of the cost of future degradation in 1992 dollars and should be used to evaluate stream stabilization project proposals.

Horizontal variability in DTPA‐extractable iron, manganese, copper, and zinc in deep loess hill soils at the mey research station

Abstract Soil is a heterogenous mixture of solids, and therefore, has significant amount of horizontal variability in DTPA‐extractable iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn). Such variability, if too high and random, may cause difficulties in interpreting the experimental data at a research station. But the level of variability of Fe, Mn, Cu, and Zn, and whether it is random or spatially correlated, has not been determined. Therefore, to determine the coefficient of variation and whether it is random or spatially correlated, fields at the MEY Research Station were divided into small plots and a composite sample was collected from each plot and analyzed for DTPA‐extractable Fe, Mn, Cu, and Zn. The weighted mean of the coefficient of variation for the whole station for Fe, Mn, Cu, and Zn was 47, 60, 38, and 47%, respectively. In addition, the variation in Fe, Mn, Cu, and Zn levels in each field, as small as 0.3 ha, was random and not spatially correlated. To reduce the effect of this random v...

A Decision Support System for Evaluating the Effects of Alternative Farm Management Systems on Water Quality and Economics

A prototype Multi-Objective Decision Support System (MODSS) for water quality has been developed by the Agricultural Research Service at the Southwest Watershed Research Center in Tucson, Arizona. The Decision Support System uses a simulation model to predict the impact of alternative management systems on surface and groundwater quality as well as farm income. The results of the simulation, which includes modeling of hydrology, erosion, nutrient and pesticide transport, crop growth and economics, are analyzed with respect to the multiple objectives of reducing surface and groundwater pollution while maintaining or improving farm income. Often these objectives are in conflict and objectively discerning which practice is preferred can be a difficult task. The multi-objective decision making component of the decision support system makes use of dimensionless utility functions and the concept of importance order dominance. The MODSS allows the user to set up alternatives, choose the decision criteria, and accept or customize the decision mode settings. The results are presented graphically as well as in tabular form. The dominance of one practice over another, if it exists, is clearly evident in the graphical presentation. We illustrate the decision component of the MODSS with pictures of the screens from an example which uses the simulation results of several management alternatives on farmland in the Deep Loess Soil Major Land Resource Area near Treynor, Iowa.

Horizontal variability in soil fertility of deep loess hill soils at MEY research station

Abstract In order to determine the level of horizontal variability, identify its nature in terms of patterns, and propose fertilizer recommendations using coefficient of variability as a factor; eight fields were selected and divided into small units at the MEY Research Station in deep loess hill soils of Northwest Missouri. The size of each unit ranged between 37 to 744 square meters and the size of the field ranged between 0.3 to 1.8 ha. A composite soil sample was collected from each unit and analyzed for extractable P, K, Ca, Mg, organic matter (OM) content, and salt pH. The coefficient of variation of each test in each field was computed. The data indicated that the weighted mean of the coefficient of variation of the whole experimental area (6.1 hectares) for pH, P, K, Ca, Mg, and OM was 5, 43, 35, 16, 24, and 54 percent, respectively. There appeared to be some low and high points in soil test levels of each field, but the patterns were not large enough to justify variable fertilizer application or ...

MULTIPLE REGRESSION ANALYSIS OF SOIL PROPERTIES ON ERODED AND NATIVE DEEP LOESS MISSOURI SOILS

Researchers have described the difficulty of studying the effects of cultivation on soil properties unless native (uncultivated) areas can be used as a baseline for comparison. Even when suitable areas are located the problems of quantifying and comparing the horizontal and vertical distributions of soil properties remain. Areal distributions of soil surface, subsurface, and upper subsoil properties were compared in cultivated and forested deep loess soils on similar geomorphic surfaces and hillslope positions in two counties adjacent to the Missouri River. A 3-dimensional grid was used to sample selected soils from the summit to the lower backs lope on 3 forested and 3 cultivated hillslopes . Multiple regress ion analysis revealed that a second order response surface equation adequately modeled the depths to maximum clay percentage and thickness of "A" horizon and a third-order response surface adequately modeled thickness of the subsurface horizon and depth to top of "B" horizon, based on the independent variables percent slope, distance from hillslope summit, and site management. Further analysis showed that each site had a significantly different response surface which could be related to site characteristics and current cover (forest or cultivation). The use of analysis of variance within multiple regression allowed for the systematic description and comparison of soil properties on forested and cultivated sites, and for the determination of the relationship between the selected soil properties and slope and site characteristics.