A simple method to determine soil moisture regime for highly weathered tropical soils

Evapotranspiration is the combination of soil evaporation and crop transpiration. Weather parameters, crop characteristics, management and environmental factors affect evapotranspiration. Reference, potential and actual evapotranspiration are distinguished. These terms are commonly used, although some differences of their definitions can be found among researches. The potential evapotranspiration of a given crop is defined as soil evaporation and plant transpiration under unlimited soil water supply and actual meteorological conditions. According to Brutseart (1982) the potential evapotranspiration is a maximum intensity of evapotranspiration from a large surface covered completely and homogeneously with actively growing plants under conditions of unlimited availability of soil water. Allen et al. (1998) call it the crop evapotranspiration under standard conditions and define as the evapotranspiration from disease-free, well-fertilized crops, grown in large fields, under optimum soil water conditions and achieving full production under the given climatic conditions. The actual evapotranspiration is the amount of water transpired from plants and evaporated from soil surface under actual meteorological conditions and under non-optimal soil, biological, management and environmental conditions. It differs from the potential evapotranspiration due to soil water shortage or waterlogging, diseases, soil salinity, low soil fertility. According to Allen et al. (1998) the evapotranspiration from crops grown under management and environmental conditions that differ from the standard conditions defined for the potential evapotranspiration can be called the crop evapotranspiration under nonstandard conditions. The evapotranspiration from a reference surface is called the reference evapotranspiration and is denoted as ETo. A large uniform grass (or alfalfa) field is considered worldwide as the reference surface. The reference grass crop completely covers the soil, is kept short, well watered and is actively growing under optimal agronomic conditions. Reference evapotranspiration (ETo) is an important agrometeorological parameter for climatological and hydrological studies, as well as for irrigation planning and management. There are several methods to estimate ETo. The FAO Penman-Monteith (FAO PM) method has been considered as a universal standard to estimate ETo (Allen et al., 1989, 1994, 1998;

Soil moisture regime classes are required by U.S. soil taxonomy and other classification systems. Soil moisture regimes are based on long‐term daily data of soil water content, which are as a rule estimated by means of models. International Commitee on Soil Moisture and Temperature Regimes (ICOMMOTR) has proposed classifying pedoclimate on the basis of biweekly water potential. This study was conducted to validate the use of the Erosion‐Productivity Impact Calculator (EPIC) model in assessing soil water content of experimental fields placed in different European pedoclimatic conditions, to compare the pedoclimatic classification obtained with EPIC with those produced by the traditional Billaux and Newhall models, and to evaluate the results attained with the ICOMMOTR methodology. The trial was carried out over a 5‐yr period in four experimental farms. The soil water content of a meadow was measured weekly or biweekly, at 0.15‐ and 0.75‐m (or 0.45‐m) depths. The EPIC model results were compared with measured data and submitted to statistical analysis of accuracy. Predicted daily soil water from EPIC was utilized to classify the soil moisture regimes following the requirements of U.S. soil taxonomy. The traditional Billaux methodology led to an overestimation of the presence of the xeric class whereas the Newhall method overrated the ustic soil moisture regime. The ICOMMOTR classification methodology was less affected by crop and by year variability than all the other methods and performed better in differentiating the soil moisture regimes of the four study sites.

] Dai [2011] (henceforth D11) reported that the PalmerDrought Severity Index (PDSI) is superior to other statisti-cally based drought indices including the StandardizedPrecipitation Index (SPI) and the Standardized PrecipitationEvapotranspiration Index (SPEI). D11 argued that given thephysical character of the PDSI water balance model, theindex provides robust estimates of drought severity becauseit takes the preceding conditions into account, in contrast toother drought indices that are based purely on past statisticsof particular climate variable(s). However, D11 has over-estimated the ability of the PDSI to realistically simulate thedistributed soil water balance at large spatial scales, andignored the inherent complexity and multiscalar character ofdrought phenomena, which are related to more than themoisture conditions of the soil. In this comment we discussthe complex characteristics of droughts and the limitationsof the PDSI to quantify drought conditions in a variety ofhydrological systems. We describe the advantages of statis-tically based drought indices including the SPI and the SPEI.ThefactthattheSPIandtheSPEIarenot(anddonotintendtobe) physically based indices is more liberating than con-straining, especially when the physical basis of PDSI can beseriously questioned.[

Zou, W., Si, B., Han, X. and Jiang, H. 2012. The effect of long-term fertilization on soil water storage and water deficit in the Black Soil Zone in northeast China. Can. J. Soil Sci. 92: 439–448. The Black Soil Zone in northeast China is one of the most important areas of agricultural production in China and plays a crucial role in food supply. However, further improvement in crop yield hinges on effective management of soil water. There is a poor understanding of how different fertilization methods affect crop water use efficiency. The objective of this study was to examine the effect of different fertilization methods on soil water storage and deficit in Black soils. A long-term experiment was conducted at the National Field Research Station of Agro-ecosystems, at Hailun County, Heilongjiang province in northeastern China from 1999 to 2008. Three fertilizer treatments including no fertilizer (CK), inorganic fertilizer (NP) and inorganic fertilizer plus organic material (NPM) were tested. The results showed that soil water storage decreased in the order CK, NP, and NPM during the growing season and the differences in soil water storage in the active root zone (0–70 cm) and below the active root zone (70–130 cm) and soil water deficit were statistically significant among the three treatments. Due to the uneven temporal distribution of rainfall and crop water uptake, soil water content was very dynamic in all three treatments: The low soil water storage and resulting soil water deficit (defined as the monthly difference between potential evapotranspiration and soil available water storage) within the 0- to 70-cm soil profile were found in both June and July. Further, soil receiving NPM was more likely to have a soil water deficit, but less likely to have excessive water. A lower risk of excess water may result in deeper root penetration and increased water use at greater depth, and thus the water deficit under the NPM treatment may not be the limiting factor for crop production. Therefore, NPM seems a viable management practice for improving crop yields in the Black Soil Zone in northeast China, possibly due to higher soil organic carbon and nutrient supply and lower probability of excess water.

It is important, but challenging, to partition soil water balance (SWB) to understand the impacts of afforestation on soil hydrological processes. This study will investigate the partitioning of SWB by combining stable and radioactive water isotopes to quantify the effects of afforestation, and analyze the mechanism by which SWB changes through identifying the water uptake strategies of apple trees of 18 and 26 years old (A18 and A26). Compared to the reference farmland, apple orchards significantly increased evapotranspiration (ET) by 5%–10%, which in turn decreased soil water storage and deep drainage by 5%–14% and 50%–95%, respectively. Further, the partitioning of ET showed that apple tree planting increased transpiration by 15%–28% but decreased evaporation by 17%–30%. The above change in SWB appeared to be closely related to plant water uptake strategies. The apple trees shifted their water source from shallow (0–2 m) to deep soils (below 2 m), utilizing approximately 62% of deep soil water in the late growing season. In particular, 23% of source water may come from soil water older than 50 years. The older apple trees tended to extract more water from deeper soils (45% for A26 vs. 38% for A18). Therefore, the soil water deficit was the cumulative effects of root water uptake. The methods for SWB partitioning provides technical support for similar studies, and the findings are helpful to better understand the hydrological processes in the thick loess deposition.

Improving Simulation of Soil Water Balance Using Lysimeter Observations in a Semiarid Climate

Understanding soil water dynamics and evapotranspiration (ET) is imperative to predict the interactions between bioenergy cropping systems and water resources; yet measurements of these variables under bioenergy crops in the U.S. Southern Great Plains (SGP) are limited. The objectives of this study were to quantify and compare soil water dynamics and ET under switchgrass ( Panicum virgatum L.), biomass sorghum [ Sorghum bicolor (L.) Moench], and mixed perennial grasses managed for biofuel production. Soil water content was measured from 2011 through 2013 at Stillwater, OK, and from 2012 through 2013 at Chickasha, OK, and ET was estimated using the soil water balance approach. For these crops, soil water depletion occurred mainly above the 2.0‐m depth, suggesting negligible root water uptake below 2.0 m. Growing season soil water depletion ranged from 4 to 287 mm and was greater (α = 0.10) for sorghum than switchgrass in 2 out of 5 site‐yr, while mixed grasses exhibited the greatest soil water depletion in 1 out of 3 yr. Growing season soil water depletion was positively related to initial soil water content. Crop year ET ranged from 493 to 846 mm and was greater for switchgrass than sorghum in 2 out of 3 site‐yr. At Stillwater, average crop year ET measured for 2 yr was 676 mm for switchgrass, 630 mm for sorghum, and 717 mm for mixed grasses. In the SGP, rainfed bioenergy production systems based on biomass sorghum may consume less water per unit land area than systems based on perennial grasses.

Winter wheat (Triticum aestivum L.) is one of most important crops in the North China Plain. However, soil water deficit (SWD) often occurs due to lack of precipitation in its growing season. In this study, we introduce two semiempirical approaches, a recharge model and the crop coefficient (Kc)–reference evapotranspiration (ET0) approach, to estimate wheat actual evapotranspiration (ETa) under no SWD and slight and severe SWD conditions. The recharge model allocated ET0 to reference evaporation and reference transpiration as a function of leaf area index. In the model, ETa is limited by soil water content, and crop water extraction for ETa is distributed through the soil profile as exponential functions of soil and root depth. The Kc–ET0 approach regarded ETa under the SWD condition as a logarithmic function of soil water availability. Under no SWD condition, the recharge model simulated 10‐d ETa with a root mean square error (RMSE) of 5.58 mm and a bias of 0.95 mm compared with measurements from a large‐scale weighing lysimeter. The two approaches both estimated seasonal evapotranspiration (ET) well compared with the adjusted ET (from the soil water balance and the recharge model–simulated deep drainage). The recharge model, which simulated the seasonal ET with the RMSE of 27.8 mm and the bias of −8.0 mm, was better than the Kc–ET0 approach (RMSE = 31.7 mm and bias = −33.1 mm). The seasonal pattern of soil water stress coefficient (Ks) showed that there were faster water losses at grain‐filling stage than at other stages.

Review of <i>Rain or Shine: An Introduction to Soil Physical Properties and Processes</i> . Tyson Ochsner. Published by Oklahoma State University Libraries under the Creative Commons Attribution 4.0 International License. Version 6. Last updated 19 Jan. 2022. DOI: https://doi.org/10.17605/OSF.IO/Z4RBT

This paper presents the soil water deficit and soil water surplus obtained from soil water balance in three drainage areas of Buenos Aires province for the period from 1971 to 2010. The soil water balance had been performed using the evapotranspiration formula of Penman-Monteith and considering the soil water constants: field capacity, soil water moisture, and soil wilting point for all the different types of soils of the region. The obtained soil water deficit and surplus are considered as triggers of extreme hydrologic events. Annual threshold values of 200 mm of soil water deficit and 300 mm of soil water surplus were considered for drought and flood, respectively. It was found that almost the 25% of the floods are severe and extreme while the 50% of droughts were of these intensities. Mann-Kendall statistical test was performed, and significance trends at level 0.1 were found for drought and for two periods, one of twenty years (1991–2010) and the other of ten years (2001–2010). As a sample of the temporal evolution of both events and their trends, the results of one locality (Junin) were deeply analyzed.

Cotton (Gossypium hirsutum L.): Physiological and morphological responses to water deficits and their relationship to yield

Abstract: In this study, an approach that integrates airborne imagery data as inputs was used to improve the estimation of soil water deficit (SWD) for maize and sunflower grown under full and deficit irrigation treatments. The proposed model was applied to optimize the maximum total available soil water (TAWr) by minimizing the difference between a water stress coefficient ks and crop water stress index (1-CWSI). The optimal value of maximum TAWr was then used to calibrate a soil water balance model which in turn updated the estimation of soil water deficit. The estimates of SWD in the soil profile of both irrigated maize and sunflower fields were evaluated with the crop root zone SWD derived from neutron probe measurements and the FAO-56 SWD procedure. The results indicated a good agreement between the estimated SWD from the proposed approach and measured SWD for both maize and sunflower. The statistical analyses indicated that the maximum TAWr estimated from CWSI significantly improved the estimates of SWD, which reduced the mean absolute error (MAE) and root mean square error (RMSE) by 40% and 44% for maize and 22% for sunflower, compared with the FAO-56 model. The proposed procedure works better for crops under deficit irrigation condition. With the availability of higher spatial and temporal resolution airborne imagery during the growing season, the optimization procedure can be further improved. Keywords: soil water deficit, soil water balance model, airborne imagery, total available water, CWSI, deficit irrigation DOI: 10.3965/j.ijabe.20171003.3081 Citation: Zhang H H, Han M, Chavez J L, Lan Y B. Improvement in estimation of soil water deficit by integrating airborne imagery data into a soil water balance model. Int J Agric & Biol Eng, 2017; 10(3): 37–46.

Sensitivity of estimates of evapotranspiration (ET) for olive fields located in Andalusia (Spain) to aerodynamic parameterization in METRIC (Mapping EvapoTranspiration with high Resolution and Internalized Calibration) was evaluated to better understand behavior of the model and spatial and temporal distribution of ET from olives, with the ultimate aim of designing customized irrigation schedules. Previous METRIC analyses have primarily focused on the estimation of ET over fields of annual crops, with few applications to complex canopies such as olive. The model was compared against FAO 56-soil water balance-based ET estimations for non-irrigated olive fields. In the first comparisons METRIC model used a general equation for momentum roughness length (zom) based on a fixed function of height estimated from LAI (Leaf Area Index) that underestimated the olives height and therefore zom, so that ET derived as a residual of the energy balance was overestimated (RMSE = 1.12 mm/day) compared to the soil water balance derived ET. The Perrier roughness function based on LAI and tree canopy architecture for sparse trees, coupled with improved olive height estimates (employing tree density and canopy shape factors) improved estimates for zom. This approach produced closer comparisons to rainfall-constrained ET estimates based on soil water balance for rainfed olive orchards (RMSE = 0.25 mm/day). This study does not attempt to validate METRIC results; instead utilizes a comparative approach between two independent methodologies to improve olive ET estimation via remote sensing, with the strong advantage, over the soil water balance approach, of improved spatial resolution over large areas.

Can weighing lysimeter ET represent surrounding field ET well enough to test flux station measurements of daily and sub-daily ET?

A conceptual agricultural water productivity model considering under field capacity soil water redistribution applicable for arid and semi-arid areas with deep groundwater