Dry Topsoil Research Articles

Rainfall‐induced consolidation and sealing effects on soil erodibility during concentrated runoff for loess‐derived topsoils

AbstractFlume experiments simulating concentrated runoff were carried out on remolded silt loam soil samples (0·36 × 0·09 × 0·09 m3) to measure the effect of rainfall‐induced soil consolidation and soil surface sealing on soil erosion by concentrated flow for loess‐derived soils and to establish a relationship between soil erodibility and soil bulk density. Soil consolidation and sealing were simulated by successive simulated rainfall events (0–600 mm of cumulative rainfall) alternated by periods of drying. Soil detachment measurements were repeated for four different soil moisture contents (0·04, 0·14, 0·20 and 0·31 g g−1). Whereas no effect of soil consolidation and sealing is observed for critical flow shear stress (τcr), soil erodibility (Kc) decreases exponentially with increasing cumulative rainfall depth. The erosion‐reducing effect of soil consolidation and sealing decreases with a decreasing soil moisture content prior to erosion due to slaking effects occurring during rapid wetting of the dry topsoil. After about 100 mm of rainfall, Kc attains its minimum value for all moisture conditions, corresponding to a reduction of about 70% compared with the initial Kc value for the moist soil samples and only a 10% reduction for the driest soil samples. The relationship estimating relative Kc values from soil moisture content and cumulative rainfall depth predicts Kc values measured on a gradually consolidating cropland field in the Belgian Loess Belt reasonably well (MEF = 0·54). Kc is also shown to decrease linearly with increasing soil bulk density for all moisture treatments, suggesting that the compaction of thalwegs where concentrated flow erosion often occurs might be an alternative soil erosion control measure in addition to grassed waterways and double drilling. Copyright © 2007 John Wiley & Sons, Ltd.

The capacity of dryland lucerne for groundwater uptake

Lucerne is being widely promoted as a means of salinity prevention, due to its ability to grow roots deeper into the soil and use more water than annual crops or pastures. This helps to reduce groundwater recharge. Direct groundwater use would also help to lower water tables, but lucerne’s role in this regard is poorly understood. In this research, lucerne plants growing in 2 landscape positions (one position with access to moderately saline groundwater, and one without access to groundwater) at similar plant densities were compared in terms of their pre-dawn leaf water potentials and evapotranspiration (ET) rates during summer. Soil analysis (pH, EC, texture, and water content) indicated that soil water content below a depth of 0.9 m was the only major difference between the 2 landscape positions. Plants with access to groundwater were larger (55 v. 13 kg dry matter/ha), less stressed (–0.71 v. –1.16 MPa pre-dawn leaf water potential), and exhibited 2–3 times higher ET rates early in the morning than plants without access to groundwater. ET rates in the afternoon were similar. Total ET from plants in both landscape positions was very low relative to potential ET. We conclude that lucerne plants with access to groundwater are able to use the water to maintain lower stress levels, but not for active growth under conditions of dry topsoil and high vapour pressure deficit. Direct groundwater uptake by lucerne is likely to be low, but may be significant for salinity control in the longer term.

Interactions between litter and water availability affect seedling emergence in four familial pairs of floodplain species

Summary 1 We studied seedling emergence in four familial pairs of floodplain herbs in response to the experimental manipulation of soil moisture and litter cover to analyse (i) whether the effect of litter changes from negative under humid to positive under dry conditions, and (ii) whether the response to changing water and light conditions with increasing litter cover varies among species and plant families. 2 We carried out a controlled pot experiment using four levels of litter cover (0 g, 2 g, 4 g and 8 g litter per pot, corresponding to 0 kg m−2, 0.2 kg m−2, 0.4 kg m−2 and 0.8 kg m−2) and two levels of water-addition, leading to constantly humid substrate or intermittently dry topsoil. 3 Across water-additions, percentage emergence reached a peak at low levels of litter cover (0.2 kg m−2 and 0.4 kg m−2). There was a significant litter × water-addition interaction in six species, with positive effects of litter under intermittently dry conditions and negative or neutral effects under constantly humid conditions. Litter lowered maximum temperature as well as amplitude, and alleviated soil humidity under low water supply, while imposing increasingly shaded conditions. Analysis of species- and family-specific responses suggested that germination under a litter cover of 0.8 kg m−2 was significantly reduced in smaller-seeded species (i.e. those that tend to have higher light demands for germination). 4 Our results suggest that transfer of seed-containing plant litter can aid restoration projects if applied at 0.2–0.4 kg m−2. Below these levels, establishment of most species may be inhibited by drought, while higher amounts will increasingly suppress seedling emergence, especially of small-seeded species. 5 In addition to facilitation effects observed between living plants, dead plant remains may also exert positive effects on establishment. The sign of the litter effect on seedling emergence depends on soil humidity, with negative effects seen above a threshold amount, which is species- and family-specific and is closely related to seed size. Whether positive litter effects in grasslands are a consequence of coevolution remains to be examined.

Response of wheat genotypes efficient in P utilisation and genotypes responsive to P fertilisation to different P banding depths and watering regimes

The capacity of wheat roots to lift water from subsoil with high moisture content into dry topsoil (hydraulic lift) and the subsequent impact on P uptake from dry topsoil are poorly understood. Two experiments were set up to test the capacity of 4 wheat genotypes differing in P efficiency to take up P from the fertiliser banded in dry topsoil (with wet subsoil). The interactions among genotypes, banding depths, and watering regimes (whole-profile or subsoil-only watering) were also characterised. The root system increased soil water content from 64 to 90 g/kg soil around the P fertiliser band by taking up water in the subsoil and releasing it into the dry topsoil during the night. Phosphorus applied as a band at 20 mg P/kg soil in dry topsoil (5 cm deep) significantly increased P uptake and shoot weight compared with a nil P control. Westonia and Gutha genotypes (efficient in P utilisation, based on dry matter produced per unit of P taken up) had higher shoot weights than Aroona and Wawht 2074 (genotypes responsive to P fertilisation, based on dry matter produced per unit of P fertiliser applied). Greater growth of wheat genotypes occurred in the treatment with P fertiliser banded at a depth of 5 cm compared with 15 cm in the whole-profile watering treatment, but no difference between banding depths was noted in the subsoil-only watering treatment. Wheat genotypes responsive to P fertilisation increased P uptake and shoot weight at the 5-cm P banding depth and the whole-profile watering treatment compared with genotypes efficient in P utilisation. Phosphorus-utilisation-efficient genotypes increased shoot growth more than other genotypes in the subsoil-only watering treatment. It can be concluded that roots of various wheat genotypes lift water from wet subsoil into the dry topsoil (hydraulic lift). Phosphorus fertiliser banded at 5-cm depth in dry topsoil increased P uptake and wheat growth due to the presence of hydraulically lifted water. Genotypes that are efficient in utilising P increased shoot weight more than genotypes responsive to P fertilisers in the subsoil-only watering treatment. In contrast, P-responsive genotypes increased shoot growth more than P-utilisation-efficient genotypes when P fertiliser was banded at 5-cm depth, and a whole-profile watering regime was imposed.

Tree roots: conduits for deep recharge of soil water.

In previous work, we provided evidence from sap flow measurements that when root systems span soil layers of different moisture content, water is redistributed by roots in the direction of the difference in water potential. In addition to the phenomenon termed "hydraulic lift", where water is redistributed from depth to dry topsoil, the process of "hydraulic redistribution" includes downward transfer of water when the surface layers of soils with low permeability become wet after rainfall. In this paper, we support our previous findings with evidence from measurements of soil water and estimate the quantities of water transferred to depth following rain. Amounts of water stored at depth are not likely to be significant for drought avoidance by plants. However, downward transfer of water may be important to plant establishment and the reduction of waterlogging in certain soil types.

Root-zone hydraulic lift evaluated with the dual-probe heat-pulse technique

Roots are movers of water in the soil. One method of movement is through hydraulic lift, which occurs when plants extract water from a moist subsoil and release it into a dry topsoil. Detection of hydraulic lift has been hampered by the lack of instruments sensitive enough to measure the small amount of water moved. Recently, the dual-probe heat-pulse (DPHP) technique has been used to monitor with fine spatial resolution the soil water content in root-zones. The objective of this research was to determine if water is released by hydraulic lift, using the DPHP technique. Sunflower (Helianthus annuus L.) was grown in a column (38 cm height; 25 cm diam.; bulk density = 1.45 Mg/m3) packed with a Haynie very fine sandy loam (coarse-silty, mixed, calcareous, mesic Mollic Udifluvents; FAO-Eutric Fluvisols) with its roots divided between a top dry layer and a lower wet layer. Eight DPHP sensors installed in the soil column were used to monitor soil water content. During 24 measurement days, hydraulic lift was evident only when the plant was wilted. This occurred when the lower ‘wet’ layer had been allowed to dry and then it was re-watered. At this time, the roots in the upper dry layer released water, increasing the soil water content in the centre of the root mass by 0.019 m3/m3 (increase from 0.121 m3/m3 to 0.140 m3/m3). The soil-water increase was similar to other values reported in the literature and show it to be small.

Experimental verification of a mechanistic model to partition evapotranspiration into soil water and plant evaporation

A model that separates evapotranspiration (ET) into soil water evaporation ( E) and plant transpiration ( T), and calculates parameters associated with the water and energy balance of the soil and crop surfaces is required to understand the fate of water in different cropping systems. ENWATBAL, a mechanistic ET model, is such a model. Our objective was to test the model by comparing calculated values of ET, E, T, net irradiance ( R n), soil heat flux ( G), and soil surface temperature ( T s) with measured ones. Three field experiments were conducted throughout 1993–1995 in a structureless sandy soil either bare or planted with sorghum in Tottori, Japan. E was measured by lysimeter using both micro- and an in situ large weighing lysimeter, ET was measured with the weighing lysimeter, and T was calculated by difference ( T = ET − E). In these experiments, R n, G, and T s were also measured using standard methods. Three statistical tests, i.e., bias, RMSE and linear regression analysis were used to evaluate model performance. In all three experiments, measured and calculated values of E and T from both a bare soil and a cropped surface were in agreement with a bias close to 0.0 mm day −1 and RMSE <1.0 mm day −1. In these comparisons, slopes and intercepts were not significantly ( P = 0.05) different from 1.0 and 0.0, respectively. Furthermore, experimental results indicated that ENWATBAL correctly calculated daily ET with a bias = −0.60 mm day −1, RMSE = 0.89 mm day −1 and a slope and intercept not significantly different from 1.0 and zero. Measured and calculated values of R n and G over a bare soil were also in agreement. However, there are differences between the midnight and diurnal values of measured and calculated T s. Therefore, we concluded that the ENWATBAL model calculated ET, E, T, R n, and G within an acceptable accuracy and range for the soil and environmental conditions of our test. It is suggested that for our soil, model accuracy on the calculation of E and T s could be improved by including the formation of a dry topsoil layer.

Movement, Distribution, and Survival of Cyrtomenus bergi (Hemiptera: Cydnidae) within the Soil Profile in Experimentally Simulated Horizontal and Vertical Soil Water Gradients

Movements, distribution, and survival of Cyrtomenus bergi Froeschner were investigated in experimental vertical and horizontal soil moisture gradients. Soil moisture acted as an important guide for movement, and the insects were attracted to moist soil. In the horizontal soil moisture gradient, most insects remained at soil moisture levels far beyond field capacity, but emigrated at moisture levels below the wilting point. In vertical soil moisture gradients, C. bergi showed positive geotaxy when the top soil was moist. Conversely, emigration was induced in dry top soil even with favorable soil moisture below. High relative air humidity stimulated activity above the ground. C. bergi was generally found closer to the soil surface in the morning than in the afternoon, especially during the dry season. High relative humidity induced flight regardless of the soil moisture level.

Evaporation from cultivated soils containing rock fragments

Evaporation from bare soil surfaces represents an important water loss for agriculture in semi-arid regions. Numerous efforts have been undertaken to modify the topsoil characteristics (mulching, tillage) in order to create a thin dry topsoil that reduces evaporation. However, little attention was paid to the role of natural rock fragments in topsoils with respect to evaporation. This paper presents the results of laboratory experiments simulating evaporation from initially wet and air-dry soils containing a range of rock fragment contents, and compares them to field conditions. Evaporation was stimulated by blowing fans at one (high) evaporative demand ( E o = 7.7–9.2 mm day −1). Time domain reflectometry (TDR) was used to investigate the relation between the water content of the topsoil and the actual evaporation rate. For soils at field capacity, initial fine earth water content decreases with rock fragment content, and consequently evaporation rates decrease in the same order. For air-dry soils that received a limited amount of rain (10 and 20 mm), an opposite behaviour was observed. Initial fine earth water content and evaporation rates increase with rock fragment content. A strong positive sigmoidal relation between relative evaporation rate (actual over open-pan evaporation rates) and fine earth water content in the centre of the wetted soil section was observed during the laboratory experiments. Except for the columns covered with a mulch, there were no systematic differences in this relation between the treatments. A rock fragment mulch reduces evaporation rate at a given soil water content significantly. These trends explain the often ambivalent effects of rock fragments on evaporation rates in the field.

Effect of burning on selected soil parameters in a grass fallow shifting cultivation system in Bhutan

Grass fallow shifting cultivation is an important land use practice in the highlands of Bhutan. Part of the nutrient pool contained in soil organic matter is made available for the traditional buckwheat (Fagopyrum tataricum) crop through a highly labor intensive system exposing 250–500 MT soil ha−1 to temperatures of 500°C and above. Dry topsoil is collected in mounds and burned using plant biomass or manure and soil organic matter as fuel. Labor input ranged from 150–401 days ha−1 with land preparation accounting for 65–85% of the total requirement. The burning increased soil pH from 6.0 to 6.9 and available K from 34 to 69 mg kg−1. Soil organic C and total N were reduced from 3.3 and 0.17% to 0.8 and 0.08%, respectively. Release of P from soil organic matter and plant material and reduction in C/N ratio resulting in increased N availability are considered the most essential effects required for good crop yields. Through the burning about 16 MT of C and 470 kg N ha−1 are released into the atmosphere. Fallow periods of 15–20 years are required for the system to be sustainable.

Structures associated with strike-slip faults that bound landslide elements

Structures associated with strike-slip faults that bound landslide elements

Sweet Corn Response to Surface and Subsurface Trickle Phosphorus Fertigation

AbstractHigh‐frequency phosphorus fertigation may increase the time‐averaged P concentration in the soil solution above that expected from P solubility considerations. Where P is a yield‐limiting factor, frequent P fertigation may increase yield by stimulating P‐uptake by the roots. A field experiment was conducted on a loessial soil (Haploxeralf) high in NaHCO3‐extractable P (0.8 mmol kg−1 soil) to test the hypothesis that subsurface placement of emitters (SSR) is more effective in stimulating P uptake than surface placement (SR). Four concentrations of P in the water (Cp), 0.04,0.16,0.64, and 1.29 mol P m−3, were applied via surface or subsurface emitters to sweet corn [Zea mays (L.) Jubilee]. Marketable ear yield increased with Cp, yielding 22.9,24.3,24.9, and 28.9 t ha−1, respectively. Yield was higher for tricklers placed 30 cm below soil surface (25.2 t ha−1) than on the surface (23.5 t ha−1). Elevated Cp increased the soil solution P concentration, thereby increasing total P uptake and total dry matter production by the plants. Deep trickler placement significantly increased the fraction of total dry matter allocated to the ears, which resulted in higher marketable yield. Subsurface irrigation also reduced weed growth due to the dry top soil during the experiment.

The movement of water through cores of a dry (cracked) clay-loam grassland topsoil

Abstract Water bypassed the soil matrix through cracks and other large voids when applied to cores of dry cracked clay-loam grassland topsoil at rates in excess of 2.2 mm hr.−1. The bypassing ratio increased from 0 to 0.55 as the application rate rose from 2.2 to 21.2 mm hr.−1. It was estimated that 10–20% of rainfall bypassed the top 0.09 m of a grassland soil at Wytham, near Oxford, England, during periods of summer soil-moisture deficit.

Deleterious Effects on Yield of Drilling Fertilizer into Established Alfalfa Stands1

AbstractDrilling fertilizer into an established forage crop has been suggested as a means of increasing fertilizer availability. Experiments were conducted at Swift Current, Saskatchewan on an orthic Brown chernozem (aridic haploboroll) to investigate the effects of fertilizer rate and placement depth on the yield of an established dryland alfalfa (Medicago ✕ vuriu Martyn) stand. In one experiment phosphorus fertilizer at rates of up to 64 kg P/ha was drilled‐in to depths of 0, 5, and 10 cm and in a second experiment, N fertilizer at rates of up to 200 kg N/ha was drilled‐in to the same depths. Fertilizer rate did not affect yields in either experiment and there were no interactions between depth of placement and fertilizer rate. However, in both experiments, increasing the depth of placement decreased yields between 12 and 20% in the first year and in both experiments the yield decreases persisted for 2 or more years. In a third experiment the soil 30 cm from the row of an old established stand of alfalfa was disturbed at four depths (0, 2.5, 5 and 10 cm) with a tractor‐drawn spike to simulate a fertilizer drill. A 20% decrease in yield was observed when the soil was disturbed below 2.5 cm. It is suggested that the reduced yields were a result of mechanical damage to roots and that the persistence of the effect was due to an inability of the root to regrow in the dry topsoil common to southwest Saskatchewan. It is recommended that for established alfalfa stands all fertilizer be surface applied.

Effects of soil water content and foliar fertilization with nitrogen and phosphorus in late season on the yield and composition of wheat

Wheat was grown in reconstructed profiles of a sandy red-brown earth in pots 120 cm deep. Ammonium sulfate (90 mg nitrogen per pot) and/or monocalcium phosphate (75 mg phosphorus per pot) were added to the topsoil. In one experiment, water treatments were introduced when the wheat reached ear emergence to provide (a) dry topsoil and water shortage; (b) dry topsoil but ample water supply in the subsoil; or (c) ample water supply, with both topsoil and subsoil wet. Additional nitrogen (82–164 mg per pot as urea) and/or phosphorus (9–18 mg per pot as phosphoric acid) were added to the plants in foliar sprays after ear emergence. In a second experiment in which water treatment (b) was applied, the dry surface soil was wetted at different stages of plant growth, viz. ear emergence, anthesis or the dough stage. In both experiments the yield and concentration of nitrogen and phosphorus in the wheat were measured at maturity. Total dry matter production was little affected by the water content of the soil after ear emergence, but grain yield was increased relative to that of straw where the topsoil was wet at the dough stage. Application of nitrogen at the time of sowing generally increased the yield of grain and straw, but phosphorus had little effect on yield. Additional foliar application of nitrogen after ear emergence increased grain yield where water stress was low: foliar application of phosphorus increased grain yield only when applied with nitrogen. Nitrogen concentration in the grain was little affected by adding nitrogen to the soil but was increased by late foliar application of nitrogen. Phosphorus concentrations were increased by phosphorus and decreased by nitrogen applications.

Uptake of Zn65 from dry soil by plants

Absorption of Zn65 by plant roots from a layer of dry top soil (suction > 15 bar) was measured using a technique that obviated water stress in the plant.

Effects of depth of fertilizer placement on wheat grown under three water regimes

Wheat was grown in reconstructed profiles of a sandy red-brown earth in pots 120 cm deep. Ammonium sulphate (40 mg nitrogen per pot) and/or monocalcium phosphate (75 mg phosphorus per pot) were placed either in the topsoil at 5 cm depth or in the subsoil at 25 cm. When the wheat reached ear emergence, water treatments were introduced to provide (a) dry topsoil and water shortage; (b) dry topsoil but ample water supply in the subsoil; or (c) an ample water supply with both topsoil and subsoil wet. The yield and concentrations of nitrogen and phosphorus in the wheat and the distribution of roots in the soil were measured at maturity. Water use by the plants was calculated. Drying of the topsoil decreased grain yield and uptake of nitrogen and phosphorus by the wheat, but the effects were small compared with those of water shortage per se. Placement of nitrogen and phosphorus at 25 cm produced higher grain yields than placement at 5 cm. There was no interaction between placement depth and the water treatments: this indicated that reduced availability of nutrients because of dry topsoil after ear emergence was not a major factor limiting yield. The fertilizer treatments affected the distribution of roots more than total root length. Root growth increased at the site of placement where nitrogen and phosphorus, and to a lesser extent nitrogen alone, were applied in the subsoil; there was little effect in other parts of the profile. Efficiency of water use was increased by the application of nitrogen.

Evaluating climatic limitations for a specific agricultural enterprise

The famous East Africa Groundnut (Peanut) Scheme of the late 1940's is cited as an example of a costly miscalculation of land use that might have been prevented by climatic assessment. At the site of this scheme, in what is now central Tanzania, water is the most restrictive factor determining natural environment. Adequate soil moisture, both near the surface and in the deeper root zone, is essential for groundnut production. Soil moisture data derived for Dodoma for 30 years show that in the period mid-January to mid-April the probability that the topsoil will remain dry for at least 16 consecutive days is 57%, and drops only to 37% for 21 or more consecutive days — even though this is the “rainy season”. The analysis further indicates that the elimination of the most serious periods of moisture shortage would require irrigation, at least once a year, in about 75% of the years. Moisture supplies are optimum for December through April in only about 3% of the years in both Dodoma and Kongwa.For comparison, the same type of climatological analysis for Tifton, Georgia and Norfolk, Virginia, in the major peanut producing areas of the eastern coastal plains region of the U.S.A., indicates that 30 years produced no occurrences of dry topsoil for as long as 16 consecutive days. Also, the climate there is so suitable for growing peanuts that irrigation in only 10% of the years would practically eliminate all except the minor periods of water shortage hazard. The condition in Tifton is slightly less favorable than in Norfolk. However, even there, optimum moisture conditions were not high during the critical months.