Ploughed Soil Research Articles

Micro paddy lysimeter for monitoring solute transport in paddy environment

The micro paddy lysimeter (MPL) was developed and evaluated for its performance to simulate solute transport in paddy environment under laboratory conditions. MPLs were constructed using soil collected from Field Museum Honmachi of Tokyo University of Agriculture and Technology, Japan. For the physical characteristics of the hardpan layer, parameters such as thickness, and soil aggregate size, affecting the percolation rate were studied. For the plow layer, two types of plow soils, sieved and un-sieved soils were compared. The sieved soil plow layer was produced by mixing air-dried soils of different aggregate sizes of D > 9.50, 9.50 ≥ D > 4.75, 4.75 ≥ D > 2.0 mm and D ≤ 2.0 mm at 47.1, 19.5, 20.6, and 12.8%, respectively. The un-sieved plow layer soil was directly used after collecting from the field. Inert tracer was applied to ponding water with controlled boundary conditions to evaluate the reproducibility of the soil hydraulic characteristics. HYDRUS-1D was used to evaluate the movement of bromide tracer in the MPL. The proposed conditions of the MPL were that the hardpan layer can be made from soil aggregates smaller than 0.425 mm with 2 cm thickness and that the plow layer can be prepared with sieved or un-sieved soils. With these conditions, the obtained results proved that MPLs can be a useful tool to simulate solute transport in paddy environment.

Camouflaging of seeds treated with pesticides mitigates the mortality of wild birds in wheat and rice crops

Seeds used to plant wheat, corn and rice crops in Brazil are treated with the insecticide carbofuran associated with the dye rhodamine B, attracting granivorous birds and causing mortality during sowing. The objective of this study was to evaluate if using camouflaged seeds can minimize mortality caused by the ingestion of seeds with carbofuran. Alternatives for reducing mortality, such as using carbofuran without rhodamine B or replacing carbofuran by carbosulfan, were compared. Three experiments were carried out in regions of known bird mortality in the states of Paraná and São Paulo, Brazil, using conventional sowing over plowed soil in the traditional planting system, 15,896 kg of seeds in 111.46 ha. Bird carcasses were collected and dissected to unveil which poisoned seed treatments had caused birds' deaths. The mortality mounted to 296 birds of 11 species. Eared doves were the most numerous casualties (263). There was significant correlation between mortality and number of consumed seeds. The consumption of camouflaged seeds was lower than that of commercial seeds treated with rhodamine B. The mortality caused by seeds with both rhodamine B and carbofuran was higher than mortality caused by seeds camouflaged only with carbofuran. The replacement of carbofuran with carbosulfan also seemingly reduced mortality, but carbosulfan mortality might have been underestimated as a result of the apparent movement of affected birds after exposure. Seeds treated with carbofuran and rhodamine B and without any dye, were attractive. Because legal requirement for seeds treated with pesticides to be differentiated by dying, the substitution of rhodamine B by camouflaging must be encouraged.

Diversity of methanogenic archaeal communities in Japanese paddy field ecosystem, estimated by denaturing gradient gel electrophoresis

Diversity of methanogenic archaeal communities in Japanese paddy field ecosystem was evaluated by the denaturing gradient gel electrophoresis (DGGE) after PCR amplification of the 16S rRNA genes (16S rDNAs), sequencing analysis and data evaluation by principal component analysis. Data were obtained from samples collected from the plowed soil layer, rice roots, rice straws incorporated in soil, plant residues (mixture of weeds, rice litters, rice roots, and rice stubbles) in soil, and composing rice straw. The number of bands of DGGE profiles ranged from 12 to 26 with the highest numbers in rice roots and rice straws incorporated in soil. However, the diversity indices based on both the numbers and intensity of bands indicated that the community of the plowed soil layer was the most diverse, even, and stable. Sequencing of the main DGGE bands showed the presence of Methanomicrobiales, Methanosarcinales, Methanobacteriaceae, and Methanocellales. The plowed soil layer included all phylogenetic groups of the methanogenic archaea of the other studied habitats, with prevalence of the members of Methanomicrobiales and Methanocellales. The phylogenetic diversity was compared with that of paddy soils collected in Italy, China, and the Philippines and that of 12 anaerobic environments (fen, waste, coast, permafrost, natural gas field, bovine rumen, riparian soil, termite, ciliate endosymboints, lake sediment, landfill, and seep rumen). The phylogenetic diversity was more similar among paddy soils than with the other anaerobic environments. Probably, the methanogenic archaeal communities of the paddy field soils were characterized by indigenous members and some of the members of the community of the plowed soil layer colonized rice roots, rice straws, and plant residues.

Descomposición de hojarasca y liberación de nutrientes en plantaciones de Acacia mangium (Mimosaceae) establecidas en suelos degradados de Colombia

Several factors control the decomposition in terrestrial ecosystems such as humidity, temperature, quality of litter and microbial activity. We investigated the effects of rainfall and soil plowing prior to the establishment of Acacia mangium plantations, using the litterbag technique, during a six month period, in forests plantations in Bajo Cauca region, Colombia. The annual decomposition constants (k) of simple exponential model, oscillated between 1.24 and 1.80, meanwhile k1 y k2 decomposition constants of double exponential model were 0.88-1.81 and 0.58-7.01. At the end of the study, the mean residual dry matter (RDM) was 47% of the initial value for the three sites. We found a slow N, Ca and Mg release pattern from the A. mangium leaf litter, meanwhile, phosphorus (P) showed a dominant immobilization phase, suggesting its low availability in soils. Chemical leaf litter quality parameters (e.g. N and P concentrations, C/N, N/P ratios and phenols content) showed an important influence on decomposition rates. The results of this study indicated that rainfall plays an important role on the decomposition process, but not soil plowing.

Effect of long-term potassium application on irrigated soil potassium and on the yield and nutrient of crops

通过在宁夏灌淤土区长达14年的连续施钾和小麦秸秆还田试验, 研究钾素投入对作物产量、养分和土壤钾素状况的影响。结果表明：小麦秸秆还田和长期施用钾肥均可不同程度提高小麦和玉米的经济产量, 其中施钾年平均增产小麦244 kg·hm^-2, 玉米397 kg·hm^-2, 处理之间产量表现为氮磷钾肥配合秸秆还田>施用氮磷钾肥>氮磷肥配合秸秆还田>只施用氮磷肥。定位后8~10年施钾肥开始显著有效, 玉米显效时间早于小麦；秸秆还田和钾肥的投入均可提高籽粒和秸秆的钾素吸收量, 秸秆含钾丰富, 籽粒钾含量仅占植株钾总量的13%~17%；施用钾肥可提高作物籽粒大中微量元素含量而降低秸秆中、微量元素含量, 促进籽粒对大部分元素的吸收；长期不施钾肥处理(NP和NP+St)0~20 cm土层土壤速效钾和缓效钾含量较定位开始时下降; 所有处理土壤全钾含量均表现下降, 下降幅度为0.8~1.2 g·kg^-1。

10.1007/s11475-008-2005-2

Humic acids (HAs) in the noncalcareous chernozems developed from the colluvium of argillites and chlorite schist are characterized by a predominance of the first, relatively mobile fraction (HA-1) and a lower content of the second (HA-2) fraction. Modern nondestructive physicochemical methods for studying the chemical structure of HA macromolecules have shown that the Has in the virgin soils have approximately equal portions of aromatic and aliphatic groups. In the plowed soils, the portion of aromatic carbon increases under the impact of the intensive agricultural use of these soils and their susceptibility to wind erosion.

10.1007/s11475-008-1009-2

The revealed trends of temperature and precipitation changes between 1932 and 2001 suggest that the nearest ten years in the southern Moscow region should be characterized by the fall in soil temperatures and the rise in the soil water content during the growing season in spite of the significant shift in the water and temperature regimes of plowed soils toward the aridity and higher continentality of their climate. The resulting situation can affect agricultural production by favoring the transition from high-input farming to grass farming in the southern Moscow region.

The promise of a technology revolution in cassava bioethanol: From Thai practice to the world practice

The abundance of low-cost feedstock and the cost-effective technology are of great importance for reinforcing industrialization of bioethanol for fuel use as sustainably-sourced and eco-friendly energy. This paper describes improved techniques that increase the root productivity of cassava ( Manihot esculenta Crantz) and its conversion to bioethanol by the energy-saving technology being developed in Thailand. The productivity of cassava roots can be significantly increased from 22 to 60 tons/ha simply by applying yield improved varieties and good cultivation practices; important ones are soil plowing, high stake quality, weed control, good planting and harvesting period, land conservation with organic fertilizers and water irrigation. Currently, the world production of cassava is around 220 million tons per annum with the average yield of 12 tons/ha and the total acreage of 18.5 million ha. If the root productivity increases, for instance, by 5 tons/ha, around 90 million tons of roots are produced which can be converted to 15,000 ML of ethanol by Simultaneous Saccharification and Fermentation (SSF) process, a current production process of which cooked and enzymatically-liquefied cassava materials are subjected to saccharifying enzymes and yeasts in concert. The promising energy-saving technology for converting cassava chips to ethanol has also been introduced at a pilot scale by using a granular starch hydrolyzing enzyme in an uncooked process.

Simulation of N2O fluxes from Irish arable soils: effect of climate change and management

Emissions of nitrous oxide (N2O) from an Irish arable soil were simulated using the DeNitrification–DeComposition (DNDC) model. The soil chosen was a free-draining sandy loam typical of the majority of cereal growing land in Ireland, and one that has been previously used to test and validate DNDC-model. DeNitrification–DeComposition model was considered suitable to estimate N2O fluxes from Irish arable soils however, underestimated the flux by 24%. The objectives of this study were to estimate future N2O fluxes from a spring barley field under conventional (moulboard plowing) and reduced (chisel plowing) tillage and different N-fertilzer application rates. Three climate scenarios, a baseline of measured climatic data from the weather station at Kilkenny and a high- and low-temperature-sensitive scenarios predicted by the Hadley Global Climate Model (HadCM4) based on the AB1 emission scenario of the Intergovernment Panel on Climate Change (IPCC) were investigated. For conventional tillage under all scenarios, three peaks of N2O emissions were predicted; an early spring peak coinciding mostly with soil plowing, a mid/late spring peak coinciding with fertilizer application and an early autumn peak coinciding with residue incorporation and onset of autumn rainfall. Under reduced tillage, due to the less amount of soil disturbance, the early spring peak was not predicted. In all cases, the total amount of N2O emitted in the late spring peak due to fertilizer application was less than the sum of the other peaks. Under climate change, using the high-temperature-increase scenario, DNDC predicted an increase in N2O emissions from both conventional and reduced tillage, ranging from 58% to 88% depending upon N application rate. In contrast, annual fluxes of N2O either decreased or increased slightly in the low temperature increase scenario relative to N application (−26 to +16%). Outputs from the model indicate that elevated temperature and precipitation increase N mineralization and total denitrification leading to greater fluxes of N2O. Annual uncertainties due to the use of two different future climate scenarios were significantly high, ranging from 74% to 95% and from 71% to 90% for the conventional and reduced tillage.

CO 2 evolution from a ridge tilled and a mouldboard ploughed Luvisol in the field

This field study was initiated to measure soil CO 2 evolution of the Turiel ridge tillage system under faba bean ( Vicia faba L.) compared with mouldboard ploughing. The CO 2–C measurements were done in situ with a transportable infrared gas analyzer at different positions on the ridges and furrows and on mouldboard plough plots with and without vegetation, respectively. The CO 2 evolution at different ridge positions reflected a ridge pattern with a CO 2–C evolution in the order crown > shoulder > furrow. On a hectare basis the mouldboard ploughed soil evolved 0.11 t more CO 2–C ha −1 than ridges, and the plots with vegetation evolved 0.58 t more CO 2–C ha −1 than the plots without vegetation during the investigation period of 57 days. At higher air temperatures the soil temperature tended to be higher on ploughed plots compared to ridges. The CO 2 evolution on the planted plots decreased with time, reflecting the decreasing physiological activity of the plant roots. Overall, despite a high degree of soil disturbance, the amount of CO 2 evolved from the ridge tilled soil was lower compared to mouldboard plough tillage, probably reflecting less favorable conditions for soil microorganisms in the ridges compared to the ploughed soil.

Soil contamination by organic and inorganic pollutants at the regional scale: the case of Piedmont, Italy

Background, aim, and scope Diffuse soil contamination has often been neglected in scientific literature, as most studies focus on contaminants from point-sources (either of industrial or agricultural origin). However, soil pollution from diffuse sources is recognized as one of the major soil threats by the EU Soil Thematic Strategy. In fact, some pollutants are nowadays ubiquitarious in the soil system, and they have to be considered for the implementation of environmental legislation, the definition of clean-up values in remediation activities and, more generally, for a sustainable management of rural areas. In the literature large scale studies on diffuse contamination are few and scattered and often do not consider a wide range of contaminants, the effect of land use, the vertical variability and the potential natural contribution. Aim of this work was to provide an overview of the diffuse soil contamination on a regional scale for a large set of contaminants. Soil inorganic (Cd, Cr, Ni, Pb, Cu, Zn) and organic contaminants (polychlorinated dibenzo-p-dioxins(PCDD), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) as well as other soil general parameters were investigated on a 18 × 18 km grid covering a whole Italian region heavily industrialized and intensively cultivated. Soils were sampled at different depths both for natural–undisturbed soil and for agricultural–plow soil. Differences in the trends of investigated contaminants, as a consequence of land use, vertical variability, natural or geogenic origin, relationships among contaminants, and with main soil properties, were explored by means of enrichment factors, bi- and multi-variate statistics.

Regional Study of No‐Till Impacts on Near‐Surface Aggregate Properties that Influence Soil Erodibility

The extent to which tillage systems modify the near‐surface soil aggregate properties affecting soil's susceptibility to erosion by water and wind is not well understood. We hypothesized that an increase in soil organic carbon (SOC) content with conservation tillage systems, particularly no‐till (NT), may improve near‐surface soil aggregate properties that influence soil erodibility. This regional study assessed changes in aggregate resistance to raindrops, dry aggregate wettability, and dry aggregate stability as well as their relationships with changes in SOC content. Four long‐term (>19 yr) tillage systems including moldboard plow (MP), conventional till (CT), reduced till (RT), and NT were chosen across the central Great Plains at Hays and Tribune, KS, Akron, CO, and Sidney, NE. The kinetic energy (KE) of raindrops required to disintegrate 4.75‐ to 8‐mm aggregates from NT soils equilibrated at −0.03 and −155 MPa matric potential was between two and seven times greater than that required for MP and CT soils in the 0‐ to 2‐cm depth in all soils. At the same depth, the water drop penetration time (WDPT) in aggregates from NT soils was four times greater at Akron and Hays and seven times greater at Sidney and Tribune compared with that in plowed soils. Aggregates from NT soils were more stable under rain and less wettable than those from plowed soils particularly in the surface 0 to 5 cm, but RT had lesser beneficial effects than NT management. The SOC content increased with NT over MP and CT and explained 35% of the variability across soils in aggregate wettability and 28% of the variability in resistance to raindrops in the 0‐ to 2‐cm depth. Aggregate wettability explained 47% of the variability across soils in KE of raindrops required for the disintegration of aggregates. No‐till management did not affect dry aggregate‐size distribution and stability except at Akron where mean weight diameter (MWD) in RT and NT was 50% lower than in MP management in the 0‐ to 2‐cm depth. Aggregates in MP and CT soils were either stronger or equally strong when dry but less stable when wet than in NT soils. Overall, NT farming enhanced near‐surface aggregate properties affecting erosion by water but had small or no effects on dry aggregate stability.

Image processing-based study of soil porosity and its effect on water movement through Andosol intact columns

The soil pore network and marcoporosity are important factors affecting water and solute transport. The transfer of contaminants to water resources is of particular importance in the Valle de Bravo watershed as it provides 10% of the drinking water for the 20 million inhabitants of Mexico City. This watershed is composed mainly of Andosols with unique mineralogical and physical characteristics. Soil porosity is usually examined on thin sections, using various image analysis techniques. We propose a novel methodology combining image analysis and a displacement experiment to study relationships between soil structure and water tracer transport parameters. H 2 18O displacement experiments were conducted through intact soil columns sampled at three depths from a representative cultivated Andosol profile. The soil structure and pore characteristics were obtained by image analysis on thin sections obtained from each column at the end of the displacement experiment. The total 2D porosity (for pores larger than 50 μm) varied from 80% of the total section area in the topsoil to around 60% in the subsoil. Tubular pores were the most abundant in the soil profile, but ploughing of the topsoil had destroyed sections of these pores and replaced them with packing pores. Water transport in the intact subsoil columns was always in physical non-equilibrium, showing the existence of preferential flow pathways. In the topsoil, one column out of three showed no preferential flow, demonstrating that soil ploughing also homogenised pore connections. Pore connectivity was larger in the ploughed topsoil than in their deeper soil horizon counterparts. Our methodology offers a 2D quantitative characterisation of the macroporous network at 50 μm resolution and the determination of water transport parameters on the same intact soil samples. 3D characterisation of soil porosity using X-ray computed tomography (CT) gives a better picture of pore connection but usually has lower spatial resolution and a larger cost.

Changes in agrophysical properties of floodplain soils under different anthropogenic loads

Agrophysical properties of alluvial soils were studied in the floodplains of the Oka River and the small rivers of Besputa (the Oka tributary) and Pol’noi Voronezh (the Voronezh tributary). The properties of the soils under different land use types (plowland, hayfield, pasture, and meadow) were compared. The features and degrees of alteration of the properties of the floodplain soils under different uses were determined. The greatest changes in the properties were found for saturated alluvial meadow soils of the Oka River floodplain under plowland. In these areas, strong degradation of the physical status of the soils was noted: compaction of the plow and subplow soil layers, an increase in the content of coarse aggregates and clods, changes in the porespace structure, and a decrease in the soil water permeability. It was shown that the soils of small river floodplains were sensitive to anthropogenic loads. In saturated alluvial soddy soils of the Besputa River floodplain, the soil water permeability decreased because of their compaction under the impact of cattle grazing. Saturated alluvial meadow soils of the Pol’noi Voronezh River floodplain were resistant to anthropogenic loads. Only a tendency towards an increase in the topsoil bulk density was observed under the impact of cattle grazing.

Degradation and abandonment of mechanized rain‐fed agricultural land in the Southern Gadarif region, Sudan: the local farmers' perception

AbstractIn the Gadarif Region of Sudan, destruction of the natural vegetation for agricultural expansion is one of the major causes of the degradation of renewable resources and the environment. This study identifies and analyses the farmers' attitudes and perceptions towards agricultural land degradation and abandonment. The cross‐sectional data collected from ten key informants and 41 large‐scale farmers focussed on the degradation and abandonment of mechanized agricultural land. The results of the study show that the respondents are well aware that soil degradation is in various forms are taking place on their cultivated agricultural land. This is based on their perception and interpretation of indicators such as weed infestation, poor soil fertility and soil compaction. Continuous cropping, mono‐cropping, rainfall shortage and the use of inferior seeds are the main reasons of land degradation as indicated by farmers. The main measures acknowledged to maintain and improve land productivity are repeated soil ploughing, abandonment/fallow periods and crop rotation.The study adduces evidence of widespread land degradation. The mitigation measures followed by the farmers may though not be sufficient to restore the soil fertility. The application of appropriate chemical fertilizers, sound crop rotation and long fallow periods can be recommended. Any management and research intervention regarding the problem of land degradation should; however, be concerted with the farmers' knowledge. Copyright © 2009 John Wiley & Sons, Ltd.

Interactive Effects of Tillage and Mineral Fertilization on Soil Carbon Profiles

Both tillage and fertilizer management influence soil organic C (SOC) storage, but their interactive effects remain to be determined for various soil and climatic conditions. We evaluated the long‐term effects of tillage (no‐till, NT, and moldboard plowing, MP), and N and P fertilization on SOC stocks and concentrations in profiles of a clay loam soil (clayey, mixed, mesic Typic Humaquept). Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were grown in a yearly rotation for 14 yr. Our results showed that NT enhanced the SOC content in the soil surface layer, but MP resulted in greater SOC content near the bottom of the plow layer. When the entire soil profile (0–60 cm) was considered, both effects compensated each other, which resulted in statistically equivalent SOC stocks for both tillage practices. Nitrogen and P fertilization with MP increased the estimated crop C inputs to the soil but did not significantly influence SOC stocks in the whole soil profile. At the 0‐ to 20‐cm depth, however, lower C stocks were measured in the plowed soil with the highest N fertilizer level than in any other treatment, which was probably caused by a greater decomposition of crop residues and soil organic matter. Conversely, the highest SOC stocks of the 0‐ to 20‐cm soil layer were observed in the NT treatment with the highest N rates, reflecting a greater residue accumulation at the soil surface. When accounting for the whole soil profile, the variations in surface SOC due to tillage and fertilizer interactions were masked by tillage‐induced differences in the 20‐ to 30‐cm soil layer.

Ammonia volatilization following surface application of urea to tilled and no-till soils: A laboratory comparison

Broadcasting of urea to agricultural soils can result in considerable losses by NH 3 volatilization. However, it is unclear if the impact of this practice on NH 3 emissions is further enhanced when performed on no-till (NT) soils. The objective of this study was to compare NH 3 volatilization following broadcasting of urea to NT and moldboard plowed (MP) soils. Intact soil cores were taken shortly after harvest from NT and MP plots of three long-term tillage experiments in Québec (Canada) and stored for 4.5 months prior to incubation. Urea (14 g N m −2) was applied at the soil surface and NH 3 volatilization was measured for 30 d using an open incubation system. Mean cumulative NH 3 losses were greater ( P < 0.001) in NT (3.00 g N m −2) than in MP (0.52 g N m −2). Several factors may have contributed to the higher emissions from the NT soils. Urease activity in the top 1 cm of soils was on average 4.2 times higher in NT than in MP soils. As a result, hydrolysis of urea occurred very rapidly in NT soils as indicated by enhanced NH 3 emissions 4 h after application of urea. The presence of crop residues at the surface of NT soils also decreased contact of the urea granules with the soil, possibly reducing adsorption of NH 4 + on soil particles. Lower volatilization on the MP soils may also have partly resulted from a fraction of urea granules falling into shallow cracks. Field trials are needed to confirm our finding that NT soils bear greater potential for NH 3 volatilization following surface application of urea than MP soils.

Phosphorus losses from a subdrained clayey soil as affected by cultivation practices

Conservation tillage practices are included in the Finnish Agri-Environmental Program as phosphorus (P) loss control measures, but only few experiments have been performed to check their effectiveness in the local conditions. We studied surface and subsurface losses of P from a clayey underdrained field (Jokioinen/ Kotkanoja; Vertic Cambisol/Typic Cryaquept), with 2% mean slope, during two separate experimental periods. Primary tillage treatments of the first experimental period of three years were moldboard ploughing (to 20–23 cm depth) vs. no autumn tillage (wintertime stubble). During the second experimental period of five years, the treatments were moldboard ploughing (20–23 cm) vs. shallow (to 5–8 cm) autumn tillage. The stubble treatment of the first experimental period produced higher dissolved reactive P (DRP) losses (104–259 g ha–1 yr–1) than autumn ploughing (77–96 g ha–1 yr–1), and equally high particulate P (PP) losses (mean 660, 235–1300 g ha–1 yr–1). During the second experimental period, shallow autumn tillage produced 28% higher DRP losses (mean 120, 107–136 g ha–1 yr–1) than ploughing (83–117 g ha–1 yr–1) and 11% higher PP losses (mean 1090, 686–1336 g ha–1 yr–1) than ploughing (783–1253 g ha–1 yr–1). Surface runoff made up 28% and 16% of the total flow from the ploughed soil during the first and the second experimental period, respectively, as compared to 50% for the stubble and 44% for the shallow autumn tillage. Routing of flow between surface and subsurface pathways had a major influence on the P losses. In the relatively flat landscapes of the main agricultural areas of southern Finland, the potential for decreasing agricultural P losses by reduced tillage appears limited.;

Reclamation of saline‐sodic soil under a rice–wheat system by horizontal surface flushing

AbstractSaline sodic soil with a high content of soluble carbonates is one of the important agricultural soils on the Central Indo‐Gangetic plains and elsewhere. Conventional reclamation procedures using gypsum application followed by vertical leaching (GC) is uneconomic; high ECe and precipitation of applied gypsum, reacting with soluble carbonates, reduce the efficacy of gypsum in these soils. This paper reports results from a project designed to evaluate reclamation by irrigation of the ploughed soil and turning of soil with a power tiller followed by flushing of standing water after 24 h, a second flushing after 7 days and subsequent application of gypsum and vertical leaching (GF2). Average rice and wheat production after GF2 significantly increased (25 and 62%, respectively) over the conventional practice. Compared with conventional treatment, GF2 significantly reduced the ECe and SAR of the soil and improved physical properties such as ζ‐potential, dispersible clay content, water stable aggregates expressed as MWD, and saturated hydraulic conductivity. Split application of gypsum between flushing (GF1/2 and GF2/3) gave similar results to GF2 in terms of soil amelioration and crop production.

Linear mixing in thermal infrared temperature retrieval

Virtually all remotely sensed thermal infrared (IR) pixels are, to some degree, mixtures of different materials or temperatures: real pixels are rarely thermally homogeneous. As sensors improve and spectral thermal IR remote sensing becomes more quantitative, the concept of homogeneous pixels becomes inadequate. Quantitative thermal IR remote sensors measure radiance. Planck's Law defines a relationship between temperature and radiance that is more complex than linear proportionality and is strongly wavelength‐dependent. As a result, the area‐averaged temperature of a pixel is not the same as the temperature derived from the radiance averaged over the pixel footprint, even for blackbodies. This paper uses simple linear mixing of pixel elements (subpixels) to examine the impacts of pixel mixtures on temperature retrieval and ground leaving radiance. The results show that for a single material with one temperature distribution and with a subpixel temperature standard deviation of 6 K (daytime images), the effects of subpixel temperature variability are small but can exceed 0.5 K in the 3–5 µm band and about a third of that in the 8–12 µm band. For pixels with a 50 : 50 mixture of materials (two temperature distributions with different means) the impact of subpixel radiance variability on temperature retrieval can exceed 6 K in the 3–5 µm band and 2 K in the 8–12 µm band. Sub‐pixel temperatures determined from Gaussian distributions and also from high‐resolution thermal images are used as inputs to our linear mixing model. Model results are compared directly to these broadband thermal images of plowed soil and senesced barley. Finally, a theoretical framework for quantifying the effect of non‐homogeneous temperature distributions for the case of a binary combination of mixed pixels is derived, with results shown to be valid for the range of standard deviations and temperature differences examined herein.