Cropland Plots Research Articles

Variability of Beryllium‐7 and Its Potential for Documenting Soil and Soil Organic Carbon Redistribution by Erosion

Core Ideas The 7Be technique can quantify soil and SOC redistribution under short‐term erosion. The heavy erosion happened in the up‐middle and down‐middle location of the slope. Depending on the weather, plowing can result in a substantial increase in erosion. Limited understanding of the redistribution of soil and soil organic C (SOC) within landscapes and their corresponding delivery ratios is available. To improve this assignment, the beryllium‐7 (7Be) technique and a simple conversion model were used to estimate soil and SOC redistribution rates on a sloping cropland plot (5 m wide and 15 m long with a slope of 10°) in the hilly red soil region of southern China. Results showed that the soil erosion and deposition rates were relatively consistent with the magnitude of a rainfall event, and the estimated net soil and SOC losses were close to the measured values. These findings suggested the potential of 7Be measurements in quantifying soil and SOC redistribution patterns associated with short‐term erosion from heavy rainfalls. The spatial redistribution patterns of soil and SOC presented alternating erosion–deposition patterns from the slope crest to the bottom. Heavy erosion occurred in the upper‐ and lower‐middle regions of the slope. The estimated net soil and SOC loss were 1.14 kg m−2 and 23.00 g m−2 for tillage from spring to summer (S–S, March–July 2013), clearly exceeding the soil (0.017 kg m−2) and SOC loss (0.43 g m−2)observed for no tillage from summer to winter (S–W, July 2013–January 2014). The sediment delivery rates in the two periods were calculated to be 64.41 and 2.51%, respectively, and the SOC delivery rates were estimated to be 58.17 and 6.48%, respectively. Depending on the weather conditions, tillage can result in a substantial increase in soil and SOC loss under traditional land use.

Burrowing activity by armadillos in agroecosystems of central Argentina: Biogeography, land use, and rainfall effects

Land use change and agricultural practices are among the main factors affecting biodiversity, and require understanding of how differing species responses shape wildlife communities in rural landscapes. During the last 2–3 decades, the Pampas of central Argentina have experienced an agricultural expansion along with rapid adoption of a non-tillage system. In some areas armadillos are increasingly considered agricultural pests, not only because they can damage and contaminate silo bags and may act as direct consumers of crops, but also their burrowing activities interfere with farming practices. Here, we describe variations in activity of armadillos in the Pampas of Buenos Aires province, central Argentina, and discuss how biogeography, land use, and rainfall may have affected these species in the rural landscape. We carried out four sampling sessions between December 2011 and June 2013 (including two periods of normal rainfall and two periods of high rainfall), surveying 392 plots (196 crop fields and 196 rangelands) at 25 different localities (covering the five different ecological units of the Pampas). In each plot, we surveyed for signs (burrows and holes) along a 600×6m transect, in order to assess armadillo activity. Chaetophractus villosus (large hairy armadillo) showed the highest activity, with 5968 signs at 79% of the plots surveyed; whereas, 1866 signs of Dasypus hybridus (southern long-nosed armadillo) were found in 36% of the plots. Generalized linear mixed models revealed that C. villosus is more active mainly in the Inland Pampas and in cropland plots, whereas, D. hybridus is more active in the Flooding Pampas at plots with active livestock use. Both species showed less burrowing activity during the second year of surveys, in a period of exceptionally high rainfall. Our results suggest that the omnivorous C. villosus may have benefited from agriculturization and non-tillage, particularly in the Inland Pampas where sandy soils favor burrowing, whereas, the more myrmecophagous D. hybridus may be in retraction.

Sediment sources of Yan'gou watershed in the Loess Hilly region China under a certain rainstorm event

At present the large scale vegetation restoration and intensive oil exploiting had brought huge influence on local environment in Yan'an region. the sediment yield data form series experiment plots and hydrological monitoring station in the Yan'an watershed after one rainfall event on July 2, 2005, which included sediment from different land uses (crop-land plot, vegetation plots, hard road surface) and 3 types roads(mountain-road brunches, mountain-road, and mountain-transport way) has been analyzed. Results showed that the erosion intensity of the 3 type roads was respectively 500 t/km2, 3163 t/km2, and 13500 t/km2. The sediment from cropland and grass, shrub land was within 6-184 t/km2. It stated that sediment from road area which only covered 1% of total area accounted for 42.3% of the total sediment yield, far beyond that from other uses of land. Sediment from grass-land and shrub-land, which covered 70.5% of watershed area, shared 26.7% of the total sediment. The further analysis showed that the 41.2% of total sediment could be detained by re-vegetation. On the contrary, that road constructing brought heavy sediment which offset the benefit of vegetation restore by 58.4%. the suggestion were to adjust our strategy from slope management to the road erosion mitigationMany studies have confirmed it is an important measure to return the steep slope farming land to green, and to restore vegetation in line with local conditions to prevent soil erosion in the Loess Plateau [1, 2]. To implement the measure in western region, the researches on "Grain for Green", returning farmland to forest and grassland, has become popular [3, 4]. Many scholars studied the effects of farming land and trees and grass land on soil water storage [2, 5].Tang Keli stated that the slope land for farming was the main source of the sediment in Yellow river, and the maximum gradient slope for farming land use was 25° [6]. Many authorities not only pointed out that a far-reaching influence of land-use changes on the distribution of sediment source area but also put forward some new ideas about returning farming to green in Loess Plateau [7, 8].However, we were still not sure the contribution of returning farmland to forest and grassland on reducing sediment yield of the valley and known it was difficult to identify its contribution to the total sediment yield.Analysis on the contribution of the stream channel and slope sediment yield had some results already [9, 10]. It was still too early to make clear the relationship between the sediment sources changes of the valley and the management.At present, Ecological restoration in the Loess Plateau caused the sediment form the slope land declining [3]. Due to human economic activities, the mountain road developed rapidly, it is inevitable that road erosion has been intensified [11]. A. Rijsdijk and LA Bruijnzeel (1991), [12] based the valley Konto observation, pointed out that although the rural road in the area accounts for only 3% of the area, but the impact on the sediment of this area was tremendous. Nyssen J, Moneryersons J. et al (2002) [13] also think that road without protection is one of the main sources of sediment. Many kinds of protective measures have great importance to the road erosion control. So attentions were paid to the study on the protection all kind of roads.Then what will happen to the soil erosion of the watershed, driven by the vegetation restoration and new road construction? What will happen to the proportion of sediment quality from slope land, road area and gully?A correct understanding of the sediment sources pattern of the typical watershed is of great significance on assessment the roles of vegetation to slope management and the roles of prevention the linear path erosion.

Design and Experiment on Flank Type of Cropland Plot Breeding Wheat Drying Car

In order to meet the drying demand of breeding wheat in China, the flank type of cropland plot breeding wheat drying car was designed, which was equipped with the solar collector automatically adjusting device and ensured that with the sun azimuth maximum angle of radiation, increased heat collecting efficiency in effective time. Used alternate partition drying storehouse and double duct W type corrugated plate collector to increase the effective contact time and heating effect about dry hot air with the breeding wheat, so improved the drying efficiency of wheat seed. The test results showed that the flank type of cropland plot breeding wheat drying car could easy to move within the cropland plot, when conducive to the breeding wheat drying operations, the average drying rate was 1.471%/h, and compared with the traditional drying methods, the average drying time was relatively reduced by 36.4%.

Effects of land utilization patterns on soil microbial communities in an acid red soil based on DNA and PLFA analyses

Disturbances such as cultivation, logging, and plantation occurred widely in acid red soil area of China, yet little is known about their effects on soil microbial community which is closely related to soil function. In this study, microbial community compositions were investigated in a red soil with different long-term land utilization patterns to understand the potential effects of cultivation and vegetation successions on relevant soil functions. Land utilization patterns include restoration, degradation (logging), cropland, and pine plantation. Both DNA- and phospholipid fatty acid (PLFA)-based methods were used to measure the abundance and community structure of microorganisms. In general, DNA- and PLFA-based methods showed similar results of microbial composition, but for some parameters, only one approach showed significant differences between different land utilization patterns. Land utilization patterns showed significant effects on abundance of total microbial community, bacteria, fungi, and actinomycetes which were all lowest in the cropland plot either by PLFA or DNA analyses. 17:0 cyclo/16:1 ω7c and 19:0 cyclo/18:1 ω7c which are possibly associated with environmental stresses also varied among different land utilization patterns. Both PLFA and T-RFLP analyses showed that each land utilization pattern possessed a specific microbial community structure. These results revealed significant effects of different land utilization patterns especially cultivation and logging on soil microbial communities and suggested that we should be cautious in utilizing red soils to sustain soil properties and functions. Combination of DNA- and PLFA-based methods is effective to provide precise results of microbial composition.

Dynamics of aggregate-associated organic carbon following conversion of forest to cropland

The conversion of natural forest to cropland generally results in the loss of soil organic carbon (OC) and an increase in CO2 flux to the atmosphere. The dynamics of aggregate-associated OC after conversion to cropland are still not well understood. Such an understanding is essential for accurately estimating C flux between soil and the atmosphere. To learn more about OC dynamics after cultivation of natural forest land, we measured total soil and aggregate-associated OC in paired forest and cropland plots in Shaanxi Province, China. The cropland had been converted from adjacent forest 4, 50, and 100 yrs previously. As expected, the conversion to cropland resulted in significant declines in total soil OC concentrations and stocks. The largest decreases occurred during the early stages of cultivation. A century of cultivation decreased total soil OC stocks in the 0–20 cm depth by 0.77 kg m−2. Macroaggregate-associated OC stocks decreased, but microaggregate-associated OC stocks increased following the conversion of forest to cropland. Silt + clay-associated OC stocks were not affected. The reduction in macroaggregate-associated OC stocks was caused by declines in both the amount of soil in the macroaggregate fraction and by decreases in the concentration of macroaggregate-associated OC. The results of this study indicate the conversion of forest to cropland not only reduced total soil OC stocks, but also caused a percentage shift in the distribution of total soil OC among aggregate size classes and among soil depths. These shifts would delay the loss of OC, so the loss of OC in forest soil due to cultivation might thus be lower than expected.

Assessing the Soil Fertility Using Landsat TM Imagery and Geospatial Statistical Analysis

This paper aims to investigate the soil fertility of Shunyi District’s cropland combing remote sensing and ground census data based on the Geostatistical Analyst of ArcGIS. Firstly, Landsat TM image was used to identify the spatial distribution and estimate the cropland plot area using support vector machine (SVM) classification method, and the overall classification is 91.5 % by 435 field survey points. Then, the survey indicators were added to ArcGIS such as organic matter, available P, available K, total N, soil pH, etc. After exploring the sample data for each indicator, trend surfaces were generated using the optimum prediction models after cross validation. Finally, according to the identified cropland plots, the soil quality index (SQI) was derived to map the soil fertility of the study area. The result shows that the southwestern part and northeastern corner of this district were found to be high in soil pH, which lies in between 8.2 and 8.6. Additionally, wide variability of organic matter, total N, available P and K were noted which can be due to the extent of cultivation in these areas while the change in fertility level could be due to anthropogenic influence. When considering the soil heavy metals, Zn, Fe, Cu and Mn show almost the same distribution.

Putative ammonia‐oxidizing bacteria and archaea in an acidic red soil with different land utilization patterns

Ammonia-oxidizers play a key role in nitrification, which is important for nitrogen cycling and soil function. However, little is known about how vegetation successions and agricultural practices caused by human activities impact the ammonia-oxidizers and nitrification process. Putative ammonia-oxidizing bacteria (AOB) and archaea (AOA) communities under different land utilization patterns of restoration (forest), degradation (pasture), cropland and pine plantation were analysed in an acidic red soil based on bacterial and archaeal amoA genes together with archaeal 16S rRNA gene. Real-time PCR, terminal restriction fragment length polymorphism (T-RFLP) and sequencing of clone libraries were conducted to study their abundance and community structure. Land utilization pattern showed significant effects on the copy numbers of all these genes, but only the bacterial amoA gene correlated significantly with potential nitrification rates (PNR). The cropland plot possessed the highest bacterial amoA gene copies and PNR, while the degradation plot was opposite to that. There were no significant variations in the bacterial amoA gene structure, which was dominated by Clusters 10 and 11 in Nitrosospira. However, archaeal amoA gene structure varied among different land utilization patterns especially for the cropland. The degradation plot was dominated by Crenarchaea 1.1c-related groups from which the amoA gene could not been amplified in this study, while other plots were dominated by Crenarchaea 1.1a/b group based on archaeal 16S rRNA gene analysis. These results indicated significant effects of land utilization patterns on putative ammonia oxidizers, which were especially obvious in the degradation and cropland plots where frequent human disturbance occurred.

Livelihood strategy change and land use change —Case of Danzam Village in upper Dadu River watershed, Tibetan Plateau of China

Land use change in rural China since the 1980s, induced by institution reforms, urbanization, industrialization and population increase, has received more attention. However, case studies on how institution reforms affect farmers’ livelihood strategies and drive land use change are scarce. By means of cropland plots investigations and interviews with farmers, this study examines livelihood strategy change and land use change in Danzam Village of Jinchuan County in the upper Dadu River watershed, eastern Tibetan Plateau, China. The results show that, during the collective system period, as surplus labor forces could not be transferred to the secondary and tertiary industries, they had to choose agricultural involution as their livelihood strategy, then the farmers had to produce more grains by land reclamation, increasing multiple cropping index, improving input of labor, fertilizer, pesticide and adopting advanced agricultural techniques. During the household responsibility system period, as labors being transferred to the secondary and tertiary industries, farmers chose livelihood diversification strategy. Therefore, labor input to grain planting was greatly reduced, which drove the transformation of grain to horticulture, vegetable or wasteland and decrease of multiple cropping index. This study provides a new insight into understanding linkages among institution reforms, livelihood strategy of smallholders and land use change in rural China.

Productividad del chamizo Atriplex canescens con fines de reconversión: dos casos

With the purpose of determining the productivity range of chamizo (fourwing saltbush) in both rangeland and cropland conditions, two plots were established in kastanozem soils at two different sites. In the cropland plot the shrub was planted in furrows (FA), in the rangeland plot two mechanized agricultural practices were used: 1) contour furrows with shrubs at its upper border (CF) and 2) planted in holes (H), as water reservoirs, with creeping prickly pear acting as barrier for water catchment. Plant height and two transversal measurements of plant diameter were taken for five years. Whole plants were cut (n=64) in each condition and dry matter was determined. A geometric model was set through regression. Mean yield for plants in the cropland plot was 1.24 kg, while in rangeland yield was 0.260 and 0.244 kg for H and CF, respectively, which represents approximately 1 kg difference. Regression models showed R2 values of 0.70 and 0.81 for H and CF, respectively. For shrubs established in the cropland plot, R2 value was 0.66. The maximum means predicted were 358 and 458 kg ha-1 for FC and H, respectively. In spite of using water holding practices, the cropland soil showed higher yield than that of rangeland. Productivity in both soil conditions represents the expected yield interval for fourwing saltbush.

Livelihood diversification and cropland use pattern in agro-pastoral mountainous region of eastern Tibetan Plateau

This study examined livelihood diversification and cropland use pattern in Keerma village, located in Jinchuan County, eastern Tibetan Plateau. Through stratified random sampling survey, participatory rural appraisal, investigation of households’ plots and statistical methods, 63 households and 272 cropland plots were systemically investigated and sampled. The results show: (1) Different types of household have variety livelihood strategies, portfolio and income. Livelihood diversification and introducing and expanding off-farm activities can be the future trend, whereas, adverse natural environment, socio-economic conditions and peasants’ capabilities together affect sustainable livelihood and land use. (2) Each livelihood strategy has its own impact on land use, mainly affecting land use type and land use intensification level. (3) Diversification into off-farm activities could be the key of building sustainable livelihood and the essential approach of realizing sustainable land use in the region.

Dynamics of topsoil carbon and nitrogen along a tropical forest–cropland chronosequence: Evidence from stable isotope analysis and spectroscopy

Analyses of δ 13C and δ 15N abundances and near infrared reflectance spectroscopy (NIRS) were used to evaluate the changes in SOC and total nitrogen (TN) content along a forest–cropland chronosequence in the margins of Kakamega forest in Kenya. 300 topsoil samples were collected from 50 paired forest–cropland plots cultivated between 17 and 60 years. Changes in δ 13C values between forest and cropland soils were used to model the dynamics of forest-derived and maize-derived C. Mean residence times (MRTs) of forest-derived C in bulk topsoil samples was calculated based on changes in δ 13C with time since cultivation. An ordinal soil fertility classification developed using NIRS was evaluated against SOC and TN concentrations and δ 13C and δ 15N abundances in the topsoil. Mean δ 13C isotopic ratios increased from 24.3 ± 0.2‰ in forest to −16.3 ± 0.4‰ under cropland. Similarly, mean δ 15N isotopic ratios increased from 5.9 ± 0.1‰ in the forest sites to 6.8 ± 0.1‰ in soils cultivated sites. δ 13C and δ 15N enrichment, low levels SOC and TN concentrations were observed in soils that were designated as low fertility based on ordinal fertility classes defined by NIRS. SOC content declined from 7.27 kg C m −2 in forest soils to 2.67 kg C m −2 in soils cultivated for 60 years. A nonlinear regression model predicted there was an accretion of maize-derived C 4 carbon, attaining equilibrium at circa 4 kg C m −2 after circa 70 years. The model also predicted that after about 38 years, maize-derived C 4 carbon was the predominant input-source of bulk topsoil SOC. The minimum, maximum and mean MRTs values for forest-derived SOC were 19, 149 and 60 years, respectively. The results of this study demonstrates that δ 15N and δ 13C values offer a robust and direct technique for stable isotope techniques for understanding the dynamics of SOC and TN after conversion of forest soils to cropland.

Composition of organic matter in sandy relict and cultivated heathlands as examined by pyrolysis-field ionization MS

Unusually high SOC levels have been reported for sandy cropland soils in North-Western Europe. A potential link with their general heathland land-use history was investigated by comparing two soil pairs of relict heathland and cultivated former heathland in the Belgian sandy region. A sequential chemical fractionation yielded similar sizes in corresponding SOM fractions between the heathland and cropland soils (i.e. NaOCl resistant: 12.3–15.0 g C kg−1 and NaOCl + HF resistant: 2.6–5.3 g C kg−1). Higher amounts of clay sized N in the cropland plots can be attributed to N additions from mineral fertilizers and animal manure. Temperature resolved Pyrolysis Field Ionization Mass Spectroscopy analysis showed that the composition of both relict heathland and cultivated soils was surprisingly similar, in spite of over 60 years of intense cropland management. The mass spectra of SOM in both heathland-cropland soil pairs investigated was dominated by signals from lipids, alkylaromatics and sterols. The accumulation of this SOM rich in aliphatics was logically linked to the high input of lipids, long-chain aliphatics and sterols from heathland vegetation and the low soil pH and microbial activity. Based on the relatively high OC surface loadings of HF-extractable OM (13–44 mg C m−2 Fe and 1.2–2.3 mg C m−2 clay), direct organo-mineral bonds between OM and Fe-oxides or clay minerals seem to be only partly involved as a stabilization mechanism in these soils. The distinct bimodal shape of the thermograms indicates that OM-crosslinking could furthermore contribute substantially to SOM stabilization in these soils. This study therefore corroborates the previously proposed view that lipids may be bound in networks of alkylaromatics, the structural building blocks of OM macromolecules. We hypothesize that such binding is able to explain the measured retention of these OM components, even under several decades of cropland management.

Reconstruction of Former Halophilous Desert Vegetation at Present Cropland Sites Using Soil Characteristics

The complicated desert vegetation pattern and its links to soil conditions in the Manas River basin where the natural landscape and human land-use history are representative for NW China and even central Asia are quantitatively investigated in this study. Vegetation and soil of 47 remnant desert and 22 cropland stands along the Manas River were sampled. Soil features, including Total Organic Carbon (TOC), total and individual (\({\text{HCO}}_3^ - \), \({\text{CO}}_3^{2 - } \), Cl−, \({\text{SO}}_4^{2 - } \), K+, Na+, Ca2+, Mg2+) salt content, and physical components of both remnant desert and cropland stands were analyzed in a laboratory. In total, eight types of desert and lowland marsh communities are distinguished. Topographical conditions are found to strongly affect soil features. The topsoil is also distinguishable from the subsoil, particularly in clay content. Statistical analyses demonstrate that both silt percentage and total salt content in the soil are significant for the distribution of plant communities. Discriminant functions for the main desert and lowland marsh types were established based on their subsoil features, with accuracy up to 83%. The vegetation patterns prior to massive cultivation of 22 cropland plots were reliably interpreted from the cropland subsoil features using these discriminant functions. Twenty of them coincide very well with topological conditions, place names and records in literature, further confirming that the subsoil features have not substantially changed in the shifting from desert to cropland.

EVALUATION OF SOIL LOSS IN GUARAÍRA BASIN BY GIS AND REMOTE SENSING BASED MODEL

Environmental degradation, and specifically erosion, is a serious and extensive problem in many areas in Brazil. Prediction of runoff and erosion in ungauged basins is one of the most challenging tasks anywhere and it is especially a very difficult one in developing countries where monitoring and continuous measurements of these quantities are carried out in very few basins either due to the costs involved or due to the lack of trained personnel. The erosion processes and land use in the Guaraira River Experimental Basin, located in Paraiba state, Brazil, are evaluated using remote sensing and a runoff-erosion model. WEPP is a process-based continuous simulation erosion model that can be applied to hillslope profiles and small watersheds. WEPP erosion model have been compared in numerous studies to observed values for soil loss and sediment delivery from cropland plots, forest roads, irrigated lands and small watersheds. A number of different techniques for evaluating WEPP have been used, including one recently developed in which the ability of WEPP to accurately predict soil erosion can be compared to the accuracy of replicated plots to predict soil erosion. WEPP was calibrated with daily rainfall data from five rain gauges for the period of 2003 to 2005. The obtained results showed the susceptible areas to the erosion process within Guaraira river basin, and that the mean sediment yield could be in the order of 3.0 ton/ha/year (in an area of 5.84 ha).

Sediment and Nutrient Losses from Field-Scale Cropland Plots Treated With Animal Manure and Inorganic Fertilizer

A field-scale plot study was conducted at Virginia Tech's Prices Fork Research Farm, to evaluate the transport of nutrients in runoff from manure and fertilizer applied at P-based agronomic rates to cropland planted to corn. Simulated rainfall events representing 2- to 10-year storms in southwest Virginia, occurring 1 and 2 days following manure and fertilizer application were used to generate runoff. Plots were treated with surface applied poultry litter, surface applied and incorporated dairy manure, incorporated inorganic fertilizer, and no fertilizer (control). Application rates were based upon agronomic phosphorus (P) requirements of corn. The concentration of total suspended solids and nutrients decreased from the first to the second simulated rainfall event; however, the edge-of-field mass loss or yield increased due to increased runoff volume. Surface application of dairy manure resulted in 25–50% lower runoff volumes and 35–60% lower total suspended solid yields when compared to surface applied poultry litter. Surface applied poultry litter produced the greatest total P and dissolved reactive P losses. Results of this study suggest that manure applied based on crop P requirements can still yield significant edge-of-field nutrient losses, if rainfall occurs soon after application.

COMPARISON OF SOIL RESPIRATION IN BROAD_LEAVED KOREAN PINE FOREST AND RECLAIMED CROPLAND IN CHANGBAI MOUNTAINS, CHINA

Soil respiration is a major flux in the global carbon cycle. A small change in soil respiration may result in a large increase of atmospheric CO_(2). Land conversion has the greatest impact on the terrestrial ecosystems among the components of global change, but the effects on soil respiration are inadequately understood. Our objective was to examine the response of soil respiration to conversion from forests to agricultural lands, using broad-leaved Korean pine forest and reclaimed cropland in the Changbai Mountains. We used an Infra-red Gas Analyser (IGA) linked to a 50 cm×50 cm×15 cm chamber without a bottom. Three 50 cm×50 cm steel frames were inserted to a soil depth of 3-5 cm in randomly selected plots one day prior to measurement. When measuring, the chamber was put on the steel frame to make a closed container capturing CO_(2) from the soil surface and piping the gas of chamber through the IGA. We repeated measurements every 15 days during the growing seasons from 2003 to 2005. Diurnal and seasonal variations of soil respiration were mainly affected by soil temperatures. Soil respiration rate reached a maximum around noon in cropland plots, about six hours earlier than that in forest plots. Minimum rates occurred at 5:00 am in cropland plots and 7:00-8:00 am in forest plots. Diurnal variations were driven mostly by temperature. During the growing season, soil respiration had a statistically significant exponential relationship with soil temperatures at 5 cm depth, but was weakly correlated with soil volumetric water contents at 10 cm depth. Although soil temperatures in cropland plots were higher than those in forest plots, soil CO_(2) efflux in forest was about twice that in cropland during the growing season (May to September). During the period of measurement, soil respiration rate of cropland ranged from 23.4% to 76.3% that of forest. Therefore, vegetation types were another factor affecting soil respiration due to the change of land-use. Q_(10) values of soil respiration averaged 2.92 for forest plots and 3.07 for cropland plots, which may be overestimated. Differences in soil respiration rates and patterns between forests and croplands result from changes in abiotic and biotic factors, including soil physicochemical properties, due to land-use change.

SOIL EROSION AND SEDIMENT YIELD PREDICTION ACCURACY USING WEPP1

ABSTRACT: The objectives of this paper are to discuss expectations for the Water Erosion Prediction Project (WEPP) accuracy, to review published studies related to WEPP goodness of fit, and to evaluate these in the context of expectations for WEPP's goodness of fit. WEPP model erosion predictions have been compared in numerous studies to observed values for soil loss and sediment delivery from cropland plots, forest roads, irrigated lands and small watersheds. A number of different techniques for evaluating WEPP have been used, including one recently developed where the ability of WEPP to accurately predict soil erosion can be compared to the accuracy of replicated plots to predict soil erosion. In one study involving 1,594 years of data from runoff plots, WEPP performed similarly to the Universal Soil Loss Erosion (USLE) technology, indicating that WEPP has met the criteria of results being “at least as good with respect to observed data and known relationships as those from the USLE,” particularly when the USLE technology was developed using relationships derived from that data set, and using soil erodibility values measured on those plots using data sets from the same period of record. In many cases, WEPP performed as well as could be expected, based on comparisons with the variability in replicate data sets. One major finding has been that soil erodibility values calculated using the technology in WEPP for rainfall conditions may not be suitable for furrow irrigated conditions. WEPP was found to represent the major storms that account for high percentages of soil loss quite well—a single storm application that the USLE technology is unsuitable for—and WEPP has performed well for disturbed forests and forest roads. WEPP has been able to reflect the extremes of soil loss, being quite responsive to the wide differences in cropping, tillage, and other forms of management, one of the requirements for WEPP validation. WEPP was also found to perform well on a wide range of small watersheds, an area where USLE technology cannot be used.

Spatial variability in topsoil micronutrient contents in a one‐hectare cropland plot

Abstract The spatial variability of meso‐ (Ca and Mg) and micronutrients (Fe, Mn, Cu, Zn, and Co) was investigated in a small cultivated plot (1.8 ha) located in the Ordenes Complex, a district of basic schists in northwest Spain. The topsoil was sampled according to a nested sampling pattern to describe the spatial variability by geostatistical techniques from 0 to about 120 m. At the sampled scale results showed that the determined meso‐ and micronutrients are spatially dependent; furthermore, pH, organic carbon, cation exchange capacity (CEC) and two texture fractions, namely sand and silt content, also present a distinct ordered spatial variation. The spatial structure of the studied nutrients was analyzed and variogram models with a nugget component and two spatial components with ranges of 20 and 50 m were found to fit the experimental results. Contour maps made by block kriging allowed to identify micro‐regions with significantly high or low extractable nutrient contents. Micronutrient distribution appear to depend largely on organic C content, soil texture, cation exchange capacity and pH. The number of samples required to assess a mean value for extractable nutrient content was calculated. Reasonably accurate determination (i.e., 95% confidence and 20% relative error) of mean nutrient contents in a plot of this size and characteristics requires 16 to 20 samples. To reduce error due to spatial dependence, samples should be about 20–25 m apart.

Effects of Denudation on the Productivity of Grassland

Denudation (close mowing and removal of mulch) of ungrazed prairie and ungrazed cropland plots near Norman, Oklahoma, did not result in significant change in composition, but increased the biomass in both the priarie and cropland during the growing season. Total biomass in all plots was low in February—March, increased to a maximum in late July, and declined rapidly thereafter. Although 115 species were sampled, only the following six species contributed significantly to the total biomass: Andropogon gerardi, Panicum virgatum, Sorghastrum nutans, Andropogon scoparius, Leptoloma cognatum, and Panicum scribnerianum. Average daily productivity was very low in February—March, moderate in April, relatively high and approximately equal in May, June, and July, and negative in August and September. The cumulative productivity was moderate for April, approximately equal but relatively high during May, June, and July, but declined rapidly thereafter. The terminal standing crop of living material (early September) was considerably lower than the maximum biomass in late July. In the denuded plots, the much increased steadily in weight throughout the period of the study. The amount of mulch attained a relatively steady state in the denuded prairie by the end of the third year, and in the denuded cropland by the end of the fourth year.