Topsoil Moisture Research Articles

Microwave vegetation optical depth and inverse modelling of soil emissivity using Nimbus/SMMR satellite observations

A radiative transfer model has been used to determine the large scale effective 6.6 GHz and 37 GHz optical depths of the vegetation cover. Knowledge of the vegetation optical depth is important for satellite-based large scale soil moisture monitoring using microwave radiometry. The study is based on actual observed large scale surface soil moisture data and observed dual polarization 6.6 and 37 GHz Nimbus/SMMR brightness temperatures over a 3-year period. The derived optical depths have been compared with microwave polarization differences and polarization ratios in both frequencies and with Normalized Difference Vegetation Index (NDVI) values from NOAA/AVHRR. A synergistic approach to derive surface soil emissivity from satellite observed brightness temperatures by inverse modelling is described. This approach improves the relationship between satellite derived surface emissivity and large scale top soil moisture fromR 2=0.45 (no correction for vegetation) toR 2=0.72 (after correction for vegetation). This study also confirms the relationship between the microwave-based MPDI and NDVI earlier described and explained in the literature.

Black Cutworm Control in Field Corn at Planting Time, 1992

Abstract Granular and liquid insecticides were applied at planting time at a site near Wayne, NE on 26 May. The soil type was silty clay loam and the previous crop was alfalfa. The field was prepared by killing the alfalfa with 2,4-D and dicamba on 4 May. The plot was planted no till into slots prepared by the landowner’s planter. Residue cover was heavy. The experimental design was a randomized complete block with 4 replicates. Each treatment consisted of 2 rows 16 m long, with 2 untreated rows between each treatment; rows were 75 cm apart. Granular materials were applied in an 18 cm band by a John Deere 2 row planter equipped with a cone-belt insecticide distributor and incorporated by tines. Ambush 2 E was broadcast immediately after planting, with a 4 nozzle CO2 back pack sprayer equipped with T-jet 8002 nozzles applying approximately 177 liters/ha total volume at 25 psi. Spray width was 1.66 m. Ambush 2E was also banded with the same spray equipment but the 4 nozzle boom was replaced with a single nozzle. Band width was 37.7 cm. Topsoil moisture was adequate at time of planting and no rain fell during the evaluation period. Plots were evaluated by counting plants remaining on either side of a randomly selected 10 m length marked between the 2 treated rows. The results are given as number of plants per 20 m of row. Final plant stand count was taken on 25 Jun.

Claybacked Cutworm Control in Field Corn, 1991

Abstract Four insecticides were applied at planting time at a site near Coleridge, NE, on 11 May. The soil type was silty clay loam and the previous crop was alfalfa. The field was prepared by killing the alfalfa with 2,4-D, disking once, and using a field finisher before planting. Very little plant residue remained. The experimental design was a randomized complete block with 4 replicates. Each treatment consisted of 2 rows 16 m long, with 2 untreated rows between each treatment; rows were 76.2 cm apart. Granular materials were applied in a 17.8 cm band by a John Deere 2-row planter equipped with a cone-belt insecticide distributer and incorporated by tines. Ambush 2 E was broadcast applied immediately after planting, with a 4-nozzle CO2 back pack sprayer equipped with T-jet 8002 nozzles applying approximately 177 liters/ha total volume at 25 psi. Spray width was 1.66 m. Topsoil moisture was adequate at time of planting and no rain fell during the evaluation period. No phytotoxicity was observed. Plots were evaluated by counting plants remaining on either side of a randomly selected 6.66 m length marked between the two treated rows. Final plant stand count was taken on 6 Jun.

Soil and plant potassium optima for maize on a kaolinitic clay soil

In South Africa, there is an extreme paucity of information relating maize (Zea mays L.) yields to soil and plant K levels and most K fertilizer recommendations are highly subjective. Controversy also surrounds the practice of relating K fertilizer recommendations to estimates of yield potential. The work reported here was conducted to address these shortcomings. The yield and plant compositional response of maize to a range of soil K levels was studied for eight seasons on a Metz clay soil (clayey, kaolinitic, thermic Plinthustalf). Relative yields were related to exchangeable soil K and the leaf parameters: K content, (Ca + Mg)/K and K DRIS index. Although grain yield maxima varied from 5.85 to 10.80 Mg ha−1, 91% of the relative yield variability was explainable in terms of exchangeable soil K. Leaf-based indices were also closely related to relative yield, but were sensitive to variations in topsoil moisture status prior to sampling and were not considered diagnostically superior to the K soil test. It...

Effect of Insecticides on Survival, Development, Fecundity, and Sex Ratio in Controlled Infestations of Western Corn Rootworm (Coleoptera: Chrysomelidae)

In a 4-yr study, granular soil insecticides were applied at planting time to plots of maize, Zea mays L., infested with population densities of eggs of western corn rootworms, Diabrotica virgifera virgifera LeConte, to determine how insecticides affected survival and development of immatures and female fecundity. Survival to adulthood differed among plots treated with different insecticides as well as among years of the study. Survival was generally highest in plots treated with insecticides that were the least water soluble (chlorpyrifos and fonofos) and lowest in plots treated with compounds that were the most water soluble (carbofuran and ethoprop). Survival was highest in years when precipitation and topsoil moisture were below normal during egg hatch and larval development and lowest when these conditions were above normal. Carbofuran, ethoprop, and chlorpyrifos delayed the mean emergence date in 1981. Only carbofuran delayed emergence in 1982, and none of the insecticides affected emergence in 1985. Mean percentage of survivors that were female differed each year (range, 23.2-45.3%). Egg density did not affect sex ratio. As reflected in the significant-year-by-insecticide interaction, some insecticides were inconsistent in their effect on sex ratios. In 1981, fecundity of survivors from plots treated with carbofuran, chlorpyrifos, terbufos, and isofenphos was significantly greater than that of survivors from plots treated with phorate, fonofos, and ethoprop or that were left untreated. Insecticides did not affect timing of oviposition, which began 2 wk after emergence and peaked when beetles were 4 wk old.

Year-to-year variation in peak above-ground biomass of six salt-marsh angiosperm communities as related to rainfall deficit and inundation frequency

Peak above-ground biomass of six annually mown salt-marsh angiosperm communities was measured over a 13-year period. Top soil salinity and soil moisture content in the six communities were measured during two dry years. Over the 13-year period the communities showed a synchronous pattern in peak biomass. Year-to-year variation in this biomass could be explained by the rainfall deficit during the growing season, while inundation frequency did not contribute to the regression model. Soil salinity and soil moisture content were significantly correlated with the rainfall deficit over a 2-year study period. Climatically induced year-to-year variation in soil conditions was held responsible for the observed year-to-year variation in peak above-ground biomass.

Soil moisture regimes and credibility in the assessment of soil suitability for crops in Tuscany

Abstract. Results of recent research on moisture regimes of surface water soils and on soil credibility are summarized, and proposals are made for the use of results in soil evaluation for selected crops.Measurements of water table depth show high variability from year to year and during the same season. Soil moisture regimes seem to affect soil management more than crop yield. A probabilistic calendar is needed for the occurrence of topsoil moisture content near the lower plastic limit in periods corresponding to the most important management practices. This is required in order to assess important soil qualities like workability and trafficability.Soil erosion is greatest when superficial run‐off can create rills. This happens when run‐off shear stresses exceed a threshold proportional to soil shear strength. Consequently, soil shear strength can be used as a measure of soil resistance to erosion. Probabilistic calendars are needed on the occurrence of heavy rainstorms able to create rills when the soil is most at risk.Entries for ratings of workability, trafficability and erosion risk are outlined.

A soil water balance model for sloping land

Abstract Simulation models of soil water balance for flat land are not applicable to hill soils principally because on the latter sites significant runoff can occur before the soil reaches field capacity. Part of the data from regular measurements of topsoil (0-75 mm depth) moisture content over a 3-year period on the north aspect of a steepland yellow-brown earth soil was used to construct a simulation model which described changes soil moisture to 150 mm depth during the year. SImIlar data collected on a south aspect of the soil and also on north and south aspects of a yellowbrown loam hill soil were used to evaluate the model. A 4-layer model was developed in which the rate of soil rewetting was empirically limited according to soil moisture content and evapotranspiration rate was primarily soil-controlled. Predicted topsoil moisture levels provided similar, but generally lower values compared to actual levels especially during the summer to late winter period: The greater discrepancy during early spri...

Greenhouse evaluation of the effect of topsoil moisture and simulated rainfall on the volatilization of nitrogen from surfaceapplied urea, diammonium phosphate, and potassium nitrate

The effect of topsoil moisture content at the time of nitrogen fertilization and distribution of precipitation following N fertilization on volatile loss of surfaceapplied fertilizer N was studied in two greenhouse experiments using15N-labeled fertilizers. Loss of applied NO 3 - -N was small compared with loss of urea-N and diammonium phosphate (DAP)-N; this suggests that NH3 volatilization was the major pathway of N loss for urea and DAP. Loss of applied NO 3 - -N averaged less than 6% of that applied regardless of initial topsoil moisture or amount of precipitation. Increased initial topsoil moisture content increased losses of urea-N greatly but losses of DAP-N only slightly. Increasing depths of precipitation, added five days after N fertilization, greatly decreased loss of urea-N but had no effect on the loss of DAP-N. Variations in moisture and precipitation treatments caused losses of urea-N to vary from 40 to 6% of that applied in a slightly acidic silty loam and from 26 to 11% in a calcareous clay. Moisture and precipitation treatments caused volatilization of DAP-N to vary from 20 to 10% in the silty loam and from 40 to 27% in the calcareous clay. In a second experiment, moisture and precipitation conditions affected N loss from urea as in the previous experiment. Addition of phenylphosphorodiamidate (PPDA), a known urease inhibitor, to urea at 20 g kg−1 resulted in only a small reduction of N loss in the calcareous clay soil used.

Development of reproductive structures in field peas (Pisum sativumL.) at different densities

Abstract Two field pea cultivars, Huka and Whero, were grown under dryland conditions in Canterbury, New Zealand, at 5 plant densities ranging from 25 to 163 plants/m2. Retention of flowers and pods and development of ovule initials were investigated. Flowers per plant, pods perplant, ovule initials per pod, peas per pod, and the area of photosynthetically active tissue per plant (plant area) were all inversely related to plant density. Although Huka produced more flowers, pods, and ovule initials than Whero, Whero had the greater plant area and lost fewer of these structures. This may be related to Whero's ability to maintain a higher photosynthetic area per reproductive structure. During pod filling the topsoil moisture content was low but water was available at greater depths. Plant area and plant area index had a greater effect on the retention and development of reproductive structures, especially ovule initials, than did soil moisture. Further work is required into the role of other plant and enviro...

Runoff and soil and nutrient losses from an improved pasture at Ginninderra, Southern Tablelands, New South Wales

Plot and catchment measurements of runoff and of soil and nutrient losses were carried out on a moderately to heavily grazed (12-30 sheep/ha) phalaris-subterranean clover pasture at Ginninderra. The effects of an intense summer storm were examined by applying artificial rains of 20 mm/ 15 min on 5.6 m2 runoff plots in 1964. The pasture topsoils had high infiltration capacities (50-75 mm/h), and when dry could absorb more than 40 mm of water. Surface runoff and soil loss were inversely related to cover (as pasture, detached litter, and sheep dung). Cover values less than about 70% were associated with some large increases in runoff and soil loss, whereas at higher cover values there was relatively little reduction in runoff and soil loss. Most soil losses were small (< 5 g m-2) when runoffs were less than about 15 %, but increased rapidly with increasing runoff. Acceptable conditions of ground cover were mostly maintained on the improved pasture but their potential for soil and nutrient losses was greater than on native pasture. Pasture renovation substantially reduced surface runoff. The effects of natural rains on runoff and soil and nutrient losses were measured from 1966 to 1971 on a 88 ha experimental catchment. The amount of runoff varied with the amount and season of rainfall, from less than 1 mm (0.2% of rainfall) in a dry year to 51 mm (7%) in a wet year, with an average of 29 mm (4%) per year. Most runoffs in autumn and summer were relatively small, reflecting the high infiltration capacity of the surface soil when topsoil moisture storage was available. In spring and winter, when the topsoil was mostly wet, runoffs were greater, reflecting the much lower infiltration capacities (c. 5 mm/h) of the subsoil. Soil losses were related to the runoffs. They ranged from 4 kg to 376 kg/ha/year, with an average of 179 kg. Most of the soil was in fine suspension, little as bed load or coarse floating debris. Losses of nitrogen, phophorus, potassium and sulfur were at average rates of 0.62, 0.12, 1.93 and 0.06 kg/ha/year. The present rate of soil loss is less than the estimated past rate of topsoil development, and the rates of loss of nitrogen, phosphorus and sulfur are less than the inputs from fertilizers and legumes. With management to retain adequate ground cover, the Ginninderra pasture effectively controls runoff and soil and nutrient losses, and could be used in similar environments as a standard for soil and water conservation, as well as livestock production.

Remote sensing of surface roughness and top soil moisture of bare tilled soil with an X-band radar.

Using a ground-based radar with a single frequency in the X-band (3 cm wavelength), the feasibility of mapping soil surface roughness and top soil moisture content was investigated. In order to cover the broad range of bare-soil appearances which occur in agricultural practice, the field treatment included a number of tillage types, several degrees of soil structure change which normally occur after tillage, and different soil moisture content. Different angles between the ray beam and the irradiated land (grazing angles) were used. The shape of radar return ( gamma )-grazing angle curves were entirely determined by soil surface roughness, while their positions depended on moisture content. Although this type of radar had limited discrimination ability, mapping of roughness and moisture may be possible under certain conditions. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Effect of Constant Moisture Levels on Pythium Rot of Peanut Pods

Different constant levels of topsoil moisture were established by upward capillary movement of water from a basin through soil columns of different heights and were used to determine the influence of soil moisture on development of rot of peanut pods by Pythium myriotylum. Roots obtained water from a wet subsoil, whereas pods developed in a Pythium-infested, sandy, well-aerated topsoil. The wetter the topsoil, the higher the incidence of infected pods. However, some pod rot developed even in soil drier than the wilting range for mesophytes.

DEPTH INTERVALS AND TOPSOIL MOISTURE MEASUREMENT WITH THE NEUTRON DEPTH PROBE

From measurements and calculations using a depth probe, the relative response is estimated for soil layers of different thicknesses. For a 10 cm thick layer of soil with the instrument centre in the middle, about 40 to 70 per cent of the response is caused by this particular layer at a water content of 8 to 40 per cent by volume. For a 20 cm layer the response for similar conditions is about 65 to 85 per cent. A special calibration function for the upper (0–20 cm) soil layer is demonstrated for the neutron depth probe. It is found that the water content in this soil layer can be estimated in this way with about the same degree of accuracy as can be expected by conventional methods.

Changes in water balance components with pasture management in south-eastern Australia

A method for evaluating infiltration and evapotranspiration for experimental catchments was applied to a series of four-acre catchments near Bacchus Marsh, Victoria. Differences in run-off between two levels of native pasture production were shown to be the direct result of changes in infiltration. On the more productive pasture containing perennial grasses, the infiltration rate was higher because of a larger capacity for moisture storage in the topsoil, and higher rates of water movement in the subsoil. The conversion of both levels of native pasture to annual improved pasture was associated with a reduction in run-off in each case, due to increased evapotranspiration during periods when soil moisture conditions are assumed to be non-limiting (topsoil moisture potential less than pF 3.5). The larger deficits developed in the soil moisture store led to increased infiltration and reduced run-off from rainfall events. The use of these findings to predict run-off, and their implications for catchment management, are discussed.

The evapotranspiration component of a pastoral experimental catchment

The amount of evapotranspiration occurring from a pastoral catchment was determined by an assessment of the hydrologic balance within the catchment. A measure of the variable for changes in water content was achieved by the evaluation of soil store deficits antecedent to runoff events. Thus, the intervals of time for the determination of the amounts of evapotranspiration were confined to periods between runoff events. For those intervals when the index of topsoil moisture stress did not exceed a pF value of 3.5, a ratio of one existed between measured evapotranspiration and the index of potential evapotranspiration. With the use of this ratio in conjunction with the soil moisture record, variations in rates of evapotranspiration were presented for the years 1963 to 1966. Such data indicated that the prevailing land-use was inefficient in its consumption of water.

THE SEASONAL MOVEMENTS OF WIREWORMS (COLEOPTERA: ELATERIDAE) IN RELATION TO SOIL MOISTURE AND TEMPERATURE IN THE ORGANIC SOILS OF SOUTHWESTERN QUEBEC

AbstractA 4-year study in the virgin organic soils of southwestern Quebec revealed that most elaterid larvae moved from the subsurface to the top 10 in. of soil in early May, when the soil temperature at a depth of 4 in. was approximately 35°F. This upward movement readied its peak when the topsoil moisture content was 200% and the soil temperature at 4 in., 55°F. In early June, when the soil temperature reached 67°F, the larvae began to move downward and very few larvae were found in the first top layers of soil when the temperature was above 72°F. This downward movement lasted until the end of August and again the larvae moved up to feed near the surface of the soil until the first frost, usually recorded in mid-November. The data indicate that June to early September is generally the most favourable period for growing vegetables.

Soil moisture deficiencies in puddled pastures

Abstract The effects of a period of heavy animal treading in wet weather on the subsequent moisture status of two pasture topsoils were investigated in replicated trials on medium-textured alluvial soils. The surface soil was found to be significantly denser in the heavily-trodden plots than in the untrodden controls for as long as six months after the treading. The higher density was accompanied by a lessened ability to store water in the readily available moisture range, up to moisture contents in equilibrium with a suction of one atmosphere. Topsoil moisture contents, whether determined gravimetrically or by plaster of Paris resistance elements, were also found to be lower in the heavily trodden plots on several occasions in the six months following the treading. These observations indicate a mechanism whereby soil changes produced by incautious grazing in winter could reduce growth during the following summer.

Kansas Phytopathological Notes: 1950

As usual the weather was a very important factor in the development, distribution, and severity of crop diseases. Rainfall during June and July 1949 was above normal in most parts of the state, especially in some western counties. This produced early germination and lush fall growth of volunteer and early-sown winter wheat. Such wheat became very heavily infected with leaf rust during October and November. The combination of too much fall growth and heavy leaf rust infection rapidly depleted the top-soil moisture and weakened the plants. This favored injury from low temperatures, and large acreages of wheat in the western third of the state died during the ensuing winter. Rainfall was deficient in nearly all parts of the state during the winter and early spring of 1950. The droughty conditions continued during April, May, and June, the period of rapid growth and fruiting of the small grain crops. As a consequence of these conditions there were extremely light infections of all of the ordinary spring diseases of cereal crops such as the rusts, powdery mildew, Septoria leaf blotch, Septoria glume blotch, black chaff, basal glume rot, and scab. This was in sharp contrast with 1949 when a wet spring season favored about the heaviest infections of most of the foregoing diseases ever observed. For example the estimated loss from leaf rust of wheat (Puccinia rubigo-vera tritici) was 10 percent in 1949, the second highest on record, but was only a trace in 1950. In many localities only scattered uredia of leaf rust could be found in 1950 where extremely heavy infections had occurred in 1949. Infections of all of the other rusts of small grains also were very light in 1950. Stem rust of wheat (P. graminis tritici) occurred only as traces and could not be found in many fields. It is worthy of note, however