A Daily Water Balance Model Based on the Distribution Function Unifying Probability Distributed Model and the SCS Curve Number Method

A new daily water balance model is developed and tested in this paper. The new model has a similar model structure to the existing probability distributed rainfall runoff models (PDM), such as HyMOD. However, the model utilizes a new distribution function for soil water storage capacity, which leads to the SCS (Soil Conservation Service) curve number (CN) method when the initial soil water storage is set to zero. Therefore, the developed model is a unification of the PDM and CN methods and is called the PDM–CN model in this paper. Besides runoff modeling, the calculation of daily evaporation in the model is also dependent on the distribution function, since the spatial variability of soil water storage affects the catchment-scale evaporation. The generated runoff is partitioned into direct runoff and groundwater recharge, which are then routed through quick and slow storage tanks, respectively. Total discharge is the summation of quick flow from the quick storage tank and base flow from the slow storage tank. The new model with 5 parameters is applied to 92 catchments for simulating daily streamflow and evaporation and compared with AWMB, SACRAMENTO, and SIMHYD models. The performance of the model is slightly better than HyMOD but is not better compared with the 14-parameter model (SACRAMENTO) in the calibration, and does not perform as well in the validation period as the 7-parameter model (SIMHYD) in some areas, based on the NSE values. The linkage between the PDM–CN model and long-term water balance model is also presented, and a two-parameter mean annual water balance equation is derived from the proposed PDM–CN model.

Capacidade de Armazenamento de Água no Solo (CAD) e Características Físicas dos Solos na Avaliação da Distribuição da Água das Chuvas na Alta Bacia do Ribeirão Santo Antônio

O estudo avalia a capacidade de armazenamento de água dos solos (CAD), utiliza como objeto de avaliação os latossolos da alta bacia do ribeirão Santo Antônio no município de Iporá-Goiás. O objetivo do estudo foi avaliar a dinâmica da água da chuva na manutenção do fluxo de água na bacia. Utilizou de dados de umidade dos solos em período de déficit hídrico e de excedente para comparar o comportamento dos solos na retenção de água e na permeabilidade. Utilizou a metodologia padrão na definição do CAD, porém com ajustes específicos na obtenção da umidade e na capacidade de campo (CC) e no ponto de murcha permanente PMP, que aqui foi denominado de ponto de menor umidade residual (PMUR). Informações como dados de chuva do período, balanço hídrico climatológico no período analisado (maio de 2018 a abril de 2019) e valores de vazão obtidos mensalmente no exutório durante o período de referência fizeram parte da análise. Um total de 43,5% da água disponibilizada pela chuva escoam superficialmente, 9,5% escoam em subsuperfície, 47% da água infiltra e/ou permanece retida nos solos. Os solos apresentaram boa drenagem e, cerca de 42% da água das chuvas garantem a perenidade da bacia. Soil Water Storage Capacity (AWSC) and Physical Characteristics of Soils in the Evaluation of Rainwater Distribution in the High Basin of Santo Antônio Stream. A B S T R A C T The study evaluates the water storage capacity of soils (AWSC). It use like object of evaluation the oxissoils located at the high Santo Antônio basin. The objective of the study was to evaluate the dynamics of rainwater in maintaining the flow of water in the basin through laboratory evaluations, in addition to testing a new methodology to define the destinations of the water that reached the surface. Was used soil moisture data in a period of water deficit and surplus to compare the behavior of soils in water retention and permeability. It used the standard methodology in the definition of the AWSC but with specific adjustments in obtaining the humidity and in the field capacity (FC) and in the permanent wilting point PWP, which here was called the point of lowest residual moisture (PLRM). Information such as rainfall data for the period, climatological water balance in the period analyzed (May 2018 to April 2019) and flow values obtained monthly in the exutory during the reference period were part of the analysis. A total of 43.5% of the water provided by the rain run off superficially, 9.5% seeps in subsurface, 47% of the water seeps and / or remains trapped in the soil. The soils had good drainage and about 42% of the rainwater guarantees the basin's perpetuity. Keywords: AWSC. Permeability. Moisture. Storage.

Beneficial Effect of Biochar on Irrigated Dwarf-Green Coconut Tree

The coconut tree is considered one of the greatest consumers of irrigation water, ranging from 100 to 240 L day−1. The objective of the present study was to evaluate the effect of biochar application on decreased irrigation water needs in a 2-year irrigated dwarf coconut palm orchard field experiment. Biochar was characterized chemically and by electron microscope images. Biochar morphology presented several micropores indicating water retention potential. Amounts of biochar were tested (0, 5, 10, 20, 40 g of biochar per kg of soil), representing 0.0; 0.5; 1.0; 2.0; and 4.0 kg per plant. Micro sprinkler irrigation started following the planting of the 90-day old hybrid dwarf coconut seedlings. The impacts of the application of the biochar on the chemical attributes of the soil, biometry of the coconut plants, water storage in the 0–0.3 m soil layer, and the volume of irrigation water required by treatment were evaluated. After two years (2017 and 2018), the application of the biochar resulted in no statistically significant differences in the chemical attributes of the soil and biometric variables of plants between different treatments. The volume of annual irrigation water per plant versus biochar quantity demonstrated a decreasing effect, due to the increase of soil water storage. The dose of 40 g of biochar per kg of soil presented the highest two-year average soil water retention (0–0.3 m layer) among treatments (34, 36, 34, 38, and 45 mm, respectively), resulting in lower 2-year irrigation water demand (28, 36, 29, 28 and 20 L plant−1 day−1, respectively).

Estimation of Stagnosol Hydraulic Properties and Water Flow Using Uni- and Bimodal Porosity Models in Erosion-Affected Hillslope Vineyard Soils

Erosion has been reported as one of the top degradation processes that negatively affect agricultural soils. The study objective was to identify hydropedological factors controlling soil water dynamics in erosion-affected hillslope vineyard soils. The hydropedological study was conducted at identically-managed Jastrebarsko (location I), and Jazbina (II) and (III) sites with Stagnosol soils. Soil Hydraulic Properties (SHP) were estimated on intact soil cores using Evaporation and WP4C methods; soil hydraulic functions were fitted using HYPROP-FIT software. For Apg and Bg/Btg horizons, uni- and bimodal soil hydraulic models could be well fitted to data; although, the bimodal model performed better in particular cases where data indicated non-uniform pore size distribution. With these SHP estimations, a one-year (2020) water flow scenario was simulated using HYDRUS-1D to compare water balance results obtained with uni- and bimodal hydraulic functions. Simulation results revealed relatively similar flux distribution at each hillslope position between the water balance components infiltration, surface runoff, and drainage. However, at the bottom profile at Jastrebarsko, bimodality of the hydraulic functions led to increased drainage. Soil water storage was reduced, and the vertical movement increased due to modified soil water retention curve shapes. Adequate parameterization of SHP is required to capture the hydropedological response of heterogenous erosion-affected soil systems.

Restoration of Degraded Grassland Significantly Improves Water Storage in Alpine Grasslands in the Qinghai-Tibet Plateau

Alpine grassland has very important water conservation function. Grassland degradation seriously affects the water conservation function; moreover, there is little understanding of the change of water state during grassland restoration. Our study aims to bridge this gap and improve our understanding of changes in soil moisture during the restoration process. In this study, the water storage, vegetation, and meteorology of a non-degradation grassland (grazing intensity of 7.5 sheep/ha) and a severely degraded grassland (grazing intensity of 12–18 sheep/ha) were monitored in the Qinghai-Tibet Plateau for seven consecutive years. We used correlation, stepwise regression, and the boosted regression trees (BRT) model analyses, five environmental factors were considered to be the most important factors affecting water storage. The severely degraded grassland recovered by light grazing treatment for 7 years, with increases in biomass, litter, and vegetation cover, and a soil-water storage capacity 41.9% higher in 2018 compared to that in 2012. This increase in soil-water storage was primarily due to the increase in surface soil moisture content. The key factors that influenced water storage were listed in a decreasing order: air temperature, litter, soil heat flux, precipitation, and wind speed. Their percentage contributions to soil-water storage were 50.52, 24.02, 10.86, 7.82, and 6.77%, respectively. Current and future climate change threatens soil-water conservation in alpine grasslands; however, grassland restoration is an effective solution to improve the soil-water retention capacity in degraded grassland soils.

Effects of fallow tillage on winter wheat yield and predictions under different precipitation types

In northern China, precipitation that is primarily concentrated during the fallow period is insufficient for the growth stage, creates a moisture shortage, and leads to low, unstable yields. Yield prediction in the early growth stages significantly informs field management decisions for winter wheat (Triticum aestivum L.). A 10-year field experiment carried out in the Loess Plateau area tested how three tillage practices (deep ploughing (DP), subsoiling (SS), and no tillage (NT)) influenced cultivation and yield across different fallow periods. The experiment used the random forest (RF) algorithm to construct a prediction model of yields and yield components. Our results revealed that tillage during the fallow period was more effective than NT in improving yield in dryland wheat. Under drought condition, DP during the fallow period achieved a higher yield than SS, especially in drought years; DP was 16% higher than SS. RF was deemed fit for yield prediction across different precipitation years. An RF model was developed using meteorological factors for fixed variables and soil water storage after tillage during a fallow period for a control variable. Small error values existed in the prediction yield, spike number, and grains number per spike. Additionally, the relative error of crop yield under fallow tillage (5.24%) was smaller than that of NT (6.49%). The prediction error of relative meteorological yield was minimum and optimal, indicating that the model is suitable to explain the influence of meteorological factors on yield.