Higher Soil Water Content Research Articles

Pinus sylvestris as a missing source of nitrous oxide and methane in boreal forest.

Boreal forests comprise 73% of the world’s coniferous forests. Based on forest floor measurements, they have been considered a significant natural sink of methane (CH4) and a natural source of nitrous oxide (N2O), both of which are important greenhouse gases. However, the role of trees, especially conifers, in ecosystem N2O and CH4 exchange is only poorly understood. We show for the first time that mature Scots pine (Pinus sylvestris L.) trees consistently emit N2O and CH4 from both stems and shoots. The shoot fluxes of N2O and CH4 exceeded the stem flux rates by 16 and 41 times, respectively. Moreover, higher stem N2O and CH4 fluxes were observed from wet than from dry areas of the forest. The N2O release from boreal pine forests may thus be underestimated and the uptake of CH4 may be overestimated when ecosystem flux calculations are based solely on forest floor measurements. The contribution of pine trees to the N2O and CH4 exchange of the boreal pine forest seems to increase considerably under high soil water content, thus highlighting the urgent need to include tree-emissions in greenhouse gas emission inventories.

Continuous ridges with film mulching improve soil water content, root growth, seed yield and water use efficiency of winter oilseed rape

Limited water resources and low water use efficiency (WUE) have limited the increase in yield of winter oilseed rape (Brassica napus L.) in northwestern China for a long time. In order to determine an optimal cultivation method for increasing seed yield and improving WUE, field experiments were conducted to study the effects of various ridge-furrow and film-mulching planting patterns on soil water content, root distribution, seed yield, and WUE for three growing seasons from 2012 to 2015. Winter oilseed rape was planted in four patterns: flat planting without film mulching (CK), flat planting with film mulching (M1), ridge-furrow planting with film mulching on both ridges and furrows (M2), and ridge-furrow planting with film mulching on continuous ridges (M3). The results showed that M3 was the best at increasing soil water storage to a depth of 1.0m after rain or irrigation and at maintaining much higher soil water content in the 0–0.3m soil layer at the late growth stage. M3 produced the shortest taproots, but the largest taproot diameter and dry weight at both the seedling and pod-filling stages in all the three growing seasons. M3 also induced significantly more lateral-root proliferation in the 0–0.1 and 0.1–0.2m soil layers without much reduction of lateral-root mass density in the 0.2–0.3m layer in comparison to M1 and M2. Seed yield and WUE were the highest and evapotranspiration (ET) was the lowest in M3 in all the three growing seasons. Average seed yield was 70.0, 41.1, and 15.0% higher and average ET was 23.6, 14.3, and 9.4% lower in M3 than in CK, M1, and M2, respectively, thus improving WUE by 121.9, 64.5, and 26.8%, respectively. These results suggested that M3 was the best mulching and planting treatment for improving soil water storage, root growth, seed yield, and WUE. M3 may thus be the optimal mulching and planting pattern for the cultivation of winter oilseed rape in arid and semiarid areas.

Effect of conservation tillage on soil respiration rate and water content under wheat/maize system in North China Plain

Conservation tillage management can improve soil moisture and reduce or increase soil CO2 emission. Soil CO2 flux rate, soil moisture, and the relationship between soil respiration and temperature on North China Plain throughout a 3-year period was determined. Tillage systems were rotary tillage without crop residues (CT), rotary tillage with crop residues incorporated into the soil in winter, and no-tillage with crop residues used as mulch in summer (TW), and rotary tillage with crop residues incorporated into the soil in summer and no-tillage with crop residues used as mulch in winter (TS). Soil respiration was measured with a LI-8100 and the gravimetric method was used to identify soil water content. Soil temperature at 5 cm depth also was measured directly by Li- 8100 through a temperature sensing probe during the CO2 measurement time. The crops were winter wheat (Triticum aestivum L) and summer maize (Zea mays L). During the wheat and maize growing period, TS reduced CO2 emission when compared with CT and TW. For the first two years of this study, CT and TW had higher soil water content when compared with TS. Thus, this study suggests that conservation tillage can be useful for North China plain farmers; however, TW emitted CO2 at the highest rate level, therefore further research is needed on long term effects of those three tillage practices on respiration rate and soil moisture in that area. Key words: Crop residue, tillage, CO2, soil water content, soil respiration, North China plain.

Seasonal variation in ecosystem water use efficiency in an urban-forest reserve affected by periodic drought

Abstract The impact of extreme weather events on water-carbon coupling and ecosystem water use efficiency (WUE) in arid to semi-arid conditions is poorly understood. Evapotranspiration (ET) and gross ecosystem production (GEP) were based on continuously eddy-covariance measurements taken over an urban-forest reserve in Beijing, in a 3-year period (2012–2014) to calculate WUE (GEP:ET). Our objective was to investigate the seasonal response of WUE to changing environmental and drought conditions at different timescales. Annually, the forest produced new plant biomass at 2.6 ± 0.2 g C per kg of water loss. Within each season, interactions of surface conductance (gc) and normalized difference vegetation index (NDVI; i.e., gc × NDVI) in spring, net radiation (Rn) and air temperature (Ta; i.e., Rn × Ta) in summer, and Rn and vapor pressure deficit (D; i.e., Rn × D) in autumn were found as the significant variables explaining seasonal variation in WUE. Daily WUE correlated positively with Ta and NDVI during the growing season, but a negative relationship during excessively dry periods (i.e., 2014). Daily WUE decreased during warm and dry days or remained nearly constant at low levels due to proportional decreases in GEP and ET. An extreme drought during the leaf expansion led to a greater decline in GEP than in ET, causing WUE to be lower in 2012 and 2014 than that in 2013. In contrast, an extreme drought during the leaf coloration led to a greater decline in ET than in GEP, causing higher WUE in 2013 and 2014 than that in 2012. We concluded that: (i) high soil water content (SWC) during leaf expansion was more important than high SWC in mid-summer or autumn for maintaining a high seasonal WUE; and that (ii) seasonal water availability combined with variable drought severity and duration during periods of changing Ta, caused seasonal ET and GEP to respond differently, introducing significant variation in seasonal WUE.

Root growth, soil water variation, and grain yield response of winter wheat to supplemental irrigation

Water shortage threatens agricultural sustainability in the Huang-Huai-Hai Plain of China. Thus, we investigated the effect of supplemental irrigation (SI) on the root growth, soil water variation, and grain yield of winter wheat in this region by measuring the moisture content in different soil layers. Prior to SI, the soil water content (SWC) at given soil depths was monitored to calculate amount of irritation water that can rehydrate the soil to target SWC. The SWC before SI was monitored to depths of 20, 40, and 60 cm in treatments of W20, W40, and W60, respectively. Rainfed treatment with no irrigation as the control (W0). The mean root weight density (RWD), triphenyl tetrazolium chloride reduction activity (TTC reduction activity), soluble protein (SP) concentrations as well as catalase (CAT), and superoxide dismutase (SOD) activities in W40 and W60 treatments were significantly higher than those in W20. The RWD in 60–100 cm soil layers and the root activity, SP concentrations, CAT and SOD activities in 40–60 cm soil layers in W40 treatment were significantly higher than those in W20 and W60. W40 treatment is characterized by higher SWC in the upper soil layers but lower SWC in the 60–100-cm soil layers during grain filling. The soil water consumption (SWU) in the 60–100 cm soil layers from anthesis after SI to maturity was the highest in W40. The grain yield, water use efficiency (WUE), and irrigation water productivity were the highest in W40, with corresponding mean values of 9169 kg ha−1, 20.8 kg ha−1 mm−1, and 35.5 kg ha−1 mm−1. The RWD, root activities, SP concentrations, CAT and SOD activities, and SWU were strongly positively correlated with grain yield and WUE. Therefore, the optimum soil layer for SI of winter wheat after jointing is 0–40 cm.

Comparison of diurnal dynamics in evaporation rate between bare soil and moss-crusted soil within a revegetated desert ecosystem of northwestern China

Effects of biological soil crusts (BSCs) on soil evaporation is quite controversial in literature, being either facilitative or inhibitive, and therein few studies have actually conducted direct evaporation measurements. Continuous field measurements of soil water evaporation were conducted on two microlysimeters, i.e., one with sand soil collected from bare sand dune area and the other with moss-crusted soil collected from an area that was revegetated in 1956, from field capacity to dry, at the southeastern edge of the Tengger Desert. We mainly aimed to quantify the diurnal variations of evaporation rate from two soils, and further comparatively discuss the effects of BSCs on soil evaporation after revegetation. Results showed that in clear days with high soil water content (Day 1 and 2), the diurnal variation of soil evaporation rate followed the typical convex upward parabolic curve, reaching its peak around mid-day. Diurnal evaporation rate and the accumulated evaporation amount of moss-crusted soil were lower (an average of 0.90 times) than that of sand soil in this stage. However, as soil water content decreased to a moderately low level (Day 3 and 4), the diurnal evaporation rate from moss-crusted soil was pronouncedly higher (an average of 3.91 times) than that of sand soil, prolonging the duration of this higher evaporation rate stage; it was slightly higher in the final stage (Day 5 and 6) when soil moisture was very low. We conclude that the effects of moss crusts on soil evaporation vary with different evaporation stages, which is closely related to soil water content, and the variation and transition of evaporation rate between bare soil and moss-crusted soil are expected to be predicted by soil water content.

Morpho-physiological response to drought of progenies of Pinus taeda L. contrasting in mean growth rate

Fil: Bulfe, Nardia Maria Lujan. Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Misiones. Estacion Experimental Agropecuaria Montecarlo; Argentina

Seed Burial Depth and Soil Water Content Affect Seedling Emergence and Growth of Ulmus pumila var. sabulosa in the Horqin Sandy Land

We investigated the effects of seed burial depth and soil water content on seedling emergence and growth of Ulmus pumila var. sabulosa (sandy elm), an important native tree species distributed over the European-Asian steppe. Experimental sand burial depths in the soil were 0.5, 1.0, 1.5, 2.0 and 2.5 cm, and soil water contents were 4%, 8%, 12% and 16% of field capacity. All two-way ANOVA (five sand burial depths and four soil water contents) results showed that seed burial depths, soil water content and their interactions significantly affected all the studied plant variables. Most of the times, seedling emergence conditions were greater at the lower sand burial depths (less than 1.0 cm) than at the higher (more than 1.0 cm) seed burial depths, and at the lower water content (less than 12%) than at the higher soil water content. However, high seed burial depths (more than 1.5 cm) or low soil water content (less than 12%) reduced seedling growth or change in the root/shoot biomass ratios. In conclusion, the most suitable range of sand burial was from 0.5 to 1.0 cm soil depth and soil water content was about 12%, respectively, for the processes of seedling emergence and growth. These findings indicate that seeds of the sandy elm should be kept at rather shallow soil depths, and water should be added up to 12% of soil capacity when conducting elm planting and management. Our findings could help to create a more appropriate sandy elm cultivation and understand sparse elm woodland recruitment failures in arid and semi-arid regions.

Flooding affects the development of Plasmodiophora brassicae in Arabidopsis roots during the secondary phase of infection

Clubroot, a disease of Brassicaceae species, is caused by the soilborne pathogen Plasmodiophora brassicae. High soil water content was previously described to favour the motility of zoospores and their penetration into root cells. In this study, the effect of irrigation regimes on clubroot development during the post‐invasive secondary phase of infection was investigated. Three irrigation regimes (low, standard, high) were tested on two Arabidopsis accessions, Col‐0 (susceptible) and Bur‐0, a partially resistant line. In Col‐0, clubroot symptoms and resting spore content were higher under the ‘low irrigation’ regime than the other two regimes, thus enhancing the phenotypic contrast between the two Arabidopsis accessions. Clubroot severity under high and low irrigation regimes was evaluated in near‐isogenic lines derived from a Col‐0 × Bur‐0 cross, to assess the effect of soil moisture on the expression of each of four quantitative trait loci (QTL) controlling partial resistance. The presence of the Bur‐0 allele at the QTL PbAt5.2 resulted in reduced severity only under low irrigation, whereas the Bur‐0 allele at QTL PbAt5.1 was associated with partial resistance only under high irrigation. QTL PbAt4 reduced the number of resting spores in infected roots, but was not associated with reduced clubroot symptoms. The results indicated that soil moisture could have consequences for the secondary phase of clubroot development, depending on plant genotype. Future genetic studies may benefit from using combinations of watering conditions during the secondary stage of infection, thus opening up the possibility of identifying genetic factors expressed under specific environmental conditions.

Les amendements du sol améliorent l’installation d’Opuntia ficus-indica (L.) Mill. dans les régions arides du sud-est du Maroc

In arid and semi-desert degraded areas of Morocco, many programs aiming at planting fodder shrubs have failed due to a lack of knowledge on effective methods for their successful establishment. Here we assessed the effects of gravel mulch (T1), TeraGel hydrophilic polymers (100g) (T2) and organic matter (5L peat) (T3), as soil amendments, on the establishment of prickly pear plant (Opuntia ficus-indica (L.) Mill.). T4 is considered as control. The study was conducted at the INRA experimental station in Errachidia, southern Morocco where cladodes were planted under natural water stress conditions on half moons. Changes in soil moisture were monitored for each treatment following rainfall. T2 had the highest soil water content during the first hours, but it decreased at a higher rate compared to T1 and T3. Cladode survival was significantly greater for T1 (100% ± 0.0) followed by T3 (94% ± 0.2), then T4 (72% ± 0.5) and T2 (67% ± 0.5). At the end of the experiment period, T1 and T3 grew 25% and 32% better than the control, respectively. Modular dynamics of cladodes (nopal) was also influenced by T1 and T3 ; the average number of cladodes after 34 months was of 18 units for T1 versus 11.8 units for the control. This study highlights the importance of using gravel mulch and organic matter in prickly pear plantations to improve the effectiveness of rainwater harvesting techniques in drylands.

Interactions between soil water conditions and forest stands in boreal forests with implications for ditch network maintenance

At sites with either peat or mineral soils in large areas of boreal forests, high soil-water contents hamper tree growth and drainage can significantly increase growth. Hence, areas covering about 15 × 10 ha of northern peatlands and wet mineral soils have been drained for forestry purposes. Usually ditches gradually deteriorate, thus reducing their functionality as drains, and ditch-network maintenance (DNM) might be needed to maintain stand growth rates enabled by the original ditching. This article reviews current knowledge on establishing the need for DNM in boreal forest stands, subsequent growth responses, and the financial outcome of the activity. The issues covered in the review are: (i) ditching, changes in ditches over time and the need for DNM; (ii) interactions between soil water and both stand properties and stand management; (iii) ground-water level (GWL) and tree growth responses to DNM; and (iv) financial viability of DNM. Conclusions about the current understanding of issues related to DNM are drawn and implications for DNM in practice are summarized. Finally, gaps in knowledge are identified and research needs are suggested.6

Assessment of Model Consistency for Determination of Soil–Water Characteristic Curves

Characterization of the engineering behavior of unsaturated soil is dependent on the soil–water characteristic curve (SWCC), a graphical representation of the relationship between water content or degree of saturation and soil suction. A reasonable description of the SWCC is thus important for the accurate prediction of unsaturated soil parameters. The measurement procedure for determining the SWCC, however, is difficult, expensive, and time-consuming. During the past few decades, researchers have laid a major focus on developing empirical equations for predicting the SWCC, with a large number of empirical models suggested. One of the most crucial questions is how precisely existing equations can represent the SWCC. As different models have different ranges of capability, it is essential to evaluate the precision of the SWCC models used for each particular soil type for better SWCC estimation. It is expected that better estimation of SWCC would be achieved via a thorough statistical consistency analysis of its applicability within a particular soil class. This paper evaluates the consistency and applicability of using four different SWCC equations for defining the relationship between water content and soil suction. Optimization techniques were used to obtain the best fit of the model parameters for three main soil classes: coarse-textured (i.e., sand), medium-textured (i.e., silt), and fine-textured (i.e., clay) soils. The four SWCC models were evaluated and computed for each sample. The results show that the Brooks and Corey model and modified Gardner model was the most consistent in describing the SWCC for sand soils and clay soils, respectively. Both model predictions also exhibit compatibility with samples ranging from low to high soil water content.

Water availability in sand dunes and its implications for the distribution of Artemisia monosperma

Plants in many sand dune systems experience arid-like conditions due to low water capacity and high hydraulic conductivity of sand grain medium. Here, water availability was studied in coastal sand dunes in a Mediterranean climate on which the dominant species is a desert dwarf shrub, Artemisia monosperma. Special emphasis was put on landscape heterogeneity and contrasts between dune stabilisation states and microhabitats, conditions after rain events and in the dry season and catenary profiles. During the approximately 150day-long dry season, as well as during multiple dry spells in the rainy season, soil water content at 50cm depth was below permanent wilting point in both mobile and stabilised dunes. The open matrix between the A. monosperma dwarf shrubs was characterised by higher hydraulic conductivity and soil water content compared with soil under A. monosperma dwarf shrubs, and played an important role in supporting the dwarf shrubs. In the mobile dunes, in which there is greater open matrix area, this has resulted in higher soil water content in the dunes that increases into the adjacent interdunce, while the opposite was found in the stabilised dunes. The dominance of A. monosperma is thus related to its ability to utilise water from the open matrix, and its distribution is driven by source–sink relations between the open matrix and A. monosperma dwarf shrubs, respectively. In stabilised dunes, A. monosperma dwarf shrubs increase in size and total percentage cover, reducing water-contributing open matrix area and probably increasing competition over water. As a result, the spatial distribution pattern of A. monosperma dwarf shrubs is regular, maintaining a certain degree of open matrix to support the living dwarf shrubs, which theoretically cannot achieve a full coverage of the dune surface in this Mediterranean system.

Experimental Study of Nanometer Magnesium Oxide-Modified Clay

Nanometer magnesium oxide (NM) is used as a new type of additive for clay. Laboratory tests were performed on clay samples to study the mechanism of NM soil reinforcement. Different NM contents (0%, 1%, 2%, 3%, 4%, and 6% by weight of clay) were freely added to the soil samples, which included different water contents (10%, 16%, and 22%). Eighteen samples were prepared, and unconfined compressive strength tests were carried out. The results show that the unconfined compressive strength of the soil samples increases with NM content and decreases with higher soil water content. The addition of 6% NM to clay soil can significantly improve the strength and stability of the soil. Our study shows that NM can increase the cementation, pore filling, and water sorption of the soil particles, which contributes to significant enhancement of the solidification effect.

다변량 환경 공간변수 주성분 분석을 통한 남·북 생태계 차이

The objectives of this study are to analyze the quantitative ecological principal components of Korean Peninsula using the multivariate spatial environmental datasets and to compare the ecological difference between South and North Korea. Ecological maps with GIS(Geographical Information System) are constructed by PCA(Principal Component Analysis) based on seventeen raster(cell based) variables at 1km resolution. Ecological differences between South and North Korea are extracted by Factor Analysis using ecosystem maps masked from Korean ones. Spatial data include SRTM(Shuttle Radar Topography Mission), Temperature, Precipitation, SWC(Soil Water Content), fPAR(Fraction of Photosynthetically Active Radiation) representing for a productivity, and SR(Solar Radiation), which all cover Korean peninsula. When it performed PCA, the first three scores were assigned to red, green, and blue color. This color triplet indicates the relative mixture of the seventeen environmental conditions inside each ecological region. The first red one represents for 'physiographic conditions' worked by high elevation and solar radiation and low temperature. The second green one stands for 'seasonality' caused by seasonal variations of temperature, precipitation, and productivity. The third blue one means 'wetness condition' worked by high value such as precipitation and soil water contents. FA extraction shows that South Korea has relatively warm and humid ecosystem affected by high temperature, precipitation, and soil water contents whereas North Korea has relatively cold and dry ecosystem due to the high elevation, low temperature and precipitation. Results would be useful at environmental planning on inaccessible land of North Korea.

In situ evaluation of internal drainage in duplex soils of the Tukulu, Sepane and Swartland forms

Internal drainage is a critical hydrological process in soil water conservation. Pedological and physical properties of the South African Tukulu, Sepane and Swartland soil types were studied in respect to soil water storage and hydraulic characteristics during internal drainage. Soil profiles were excavated and classified in situ alongside instantaneous drainage plots and saturated hydraulic conductivity experiments. Laboratory desorption experiments were used to establish the soil water characteristic curves (SWCC) of diagnostic horizons. Each SWCC was then fitted with the van Genuchten 1980 model and matric suction of soil water content corresponding to the 1 200 hours drainage curves were estimated. The pedocutanic B and prismatic C horizons in the Tukulu and Sepane soils had clay plus silt content of more than 40% and were characterised by abrupt transitions, signs of wetness and a sharp drop in hydraulic conductivity at higher soil water content. Consequently, deep drainage from the Tukulu and Sepane was about 40% less than that of the Swartland. The drained upper limit was located when drainage flux rate approached 0.001 mm h−1 irrespective of soil type. At this rate deep drainage losses over the seven-month fallow period are equivalent to 1% annual rainfall.

Contrasting responses of gross primary productivity to precipitation events in a water-limited and a temperature-limited grassland ecosystem

The impact of global climate change on precipitation regimes may bring about significant consequences to the productivity of grassland ecosystems. This study reports the effects of the characteristics of precipitation events (PEC, e.g., size, frequency, interval, and seasonal distribution of precipitation events) on gross primary productivity (GPP) based on long-term measurements of net ecosystem CO2 exchange and evapotranspiration by the eddy covariance technique in a water-limited temperate steppe in Inner Mongolia and a humid but temperature-limited alpine meadow in Tibet, China. We determined that the predominant characteristics of precipitation events that affected GPP differed remarkably between these two ecosystems. The number of heavy precipitation events (>10mmday−1) was the most important PEC to impact GPP in the temperate steppe. Years with more frequent heavy precipitation events favored higher GPP. However, in contrast with the case in the temperate steppe, precipitation interval was the factor that affected GPP most in the alpine meadow. GPP was higher as the precipitation intervals lengthened or their distribution shifted to fewer but longer intervals (concentrated distribution). Additionally, the mechanisms for the effects of PEC on GPP also differed between these two ecosystems. Compared with small events, heavy precipitation events recharged deeper soil layers in the temperate steppe, which was biologically more meaningful for plant transpiration (i.e., an increase in the ratio of transpiration to evapotranspiration), relief from drought stress (an increase in the duration of high soil water content), and thereby higher GPP. In contrast, mean air temperature was higher in the alpine meadow when the precipitation intervals increased or their distribution was more concentrated, leading to a longer period of higher temperature that was favorable to higher GPP. Our results imply that soil water is not the exclusive means of revealing the mechanism of precipitation affecting productivity; the corresponding changes in temperature along with precipitation events may also play a substantial role in temperature-limited grasslands.

A comparison of microclimate and environmental modification produced by hedgerows and dehesa in the Mediterranean region: A study in the Guadarrama region, Spain

Two common forms of traditional land use systems in Mediterranean landscapes are dehesa and hedged fields. Both are agroforestry systems in which domestic stock are pastured: amongst parklike trees in dehesa, and in enclosures surrounded by stone walls and woody vegetation in hedged fields. The latter are now tending to be replaced by dehesa due to labour costs. Here, we investigate the boundary layer microclimate and environmental characteristics of these two land uses in order to evaluate the respective differences in relation to climate modification, soil organic carbon, and soil water content. Fraxinus angustifolia-dominated sites were investigated in the Guadarrama mountains, Spain, in high summer with simultaneous sampling under trees in both dehesa and hedgerows and in adjacent open fields. Whilst temperature profiles were similar in both systems, hedgerows had higher soil water content, lower wind speeds, and higher total soil organic carbon compared to dehesa, and moreover these trends also applied to open fields of the respective systems. We conclude that not only do hedged fields have advantages over dehesa for shelter and production, but that the climatic modifications of hedged field systems potentially modify boundary layer climates on a broader scale than both individual fields and dehesa. Thus, the conservation of hedged field systems provides natural capital and broad environmental gains.

Testing steady-state analysis of single-ring and square pressure infiltrometer data

Testing reliability of the saturated soil hydraulic conductivity, Ks, estimated by applying the steady-state single-ring (SR) model to the quasi steady-state infiltration rates obtained with a single-ring pressure infiltrometer (PI) increases confidence in the estimated Ks values. Determining a means to estimate Ks from infiltration data collected with a square infiltrometer allows the use of sources of different shapes. Using numerically simulated infiltration rates for six homogeneous soils ranging in texture from sand to silty clay loam, this investigation suggested an overall good performance of the SR model, with estimated Ks values differing by not more than 25% from the true values for the 90% of the 96 considered runs. Larger errors were generally obtained for the silty clay loam soil. Even in this case, however, a small ring radius (0.038m), a relatively high initial soil water content (initial effective saturation=0.4) and a relatively high depth of ponding (0.10m) allowed the obtainment of accurate predictions of Ks (error=13%) with a run of practically sustainable duration (4h). The SR model was also usable to analyze quasi steady-state infiltration data collected with a square infiltrometer when infiltration was assumed to occur through a circular source having the same area of the square infiltrometer. With this assumption, the estimates of Ks differed from the true values by not more than a practically negligible 16%. The results of this investigation should help better interpret Ks values obtained with the PI and also improve the experimental methodology, depending on the soil. Moreover, a wider applicability of the infiltrometer techniques, i.e. not limited to a circular source, can be expected. Soil heterogeneity should be taken into account in the future since heterogeneity is common in the field.

English

A two-year study was conducted on an Alfisol in the humid tropics of southwest Nigeria to investigate the effects of tillage and intercropping on soil water characteristics, performance of maize (Zea mays L.) and groundnut (Arachis hypogea L.). The experiment was a split-plot design with tillage methods as the main plot and intercropping as the sub-plots in a completely randomized design with four replications. Tillage treatments were conventional tillage (CT) and no-tillage (NT) while the cropping treatments were sole maize, sole groundnut and intercropped maize + groundnut. Gravimetric soil water content (swgc) showed that NT had higher soil water content in all cropping treatments than CT. NT had significantly (p NT intercropping > CT intercropping > sole maize CT. For groundnut, the trend was NT sole groundnut > NT intercropped > CT sole groundnut > CT intercropped. Key words: Tillage, intercropping, soil water retention, infiltration.