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Hou S.,China Agricultural University | Huang Y.,China Agricultural University | Huang Y.,Key Laboratory of Arable Land Conservation North China | Shen C.,China Agricultural University | And 3 more authors.
Nongye Jixie Xuebao/Transactions of the Chinese Society for Agricultural Machinery

Zero-tension lysimeters (ZTL) have been widely applied to monitor soil solution flux and solute transport through soil layers in the vadose zone to the ground water under various conditions in research areas, such as the comprehensive utilization of agricultural water and soil resources as well as soil and water environment conservations. A capillary barrier that can cause flow divergence around the system will be created between undisturbed soil and ZTL as the ZTLs are installed in the field. Meanwhile, the water can overcome the capillary barrier and enter into ZTL only when the soil water is saturated above the contact plane of soil and ZTL. Thus, the efficiency of adopting ZTL for water collection decreases correspondingly. To improve the collection efficiency of ZTL, divergence barrier was added to ZTL (ZTLd), and the factors that can affect the collection efficiency of ZTL were examined, such as soil hydraulic property, soil texture, irrigation rate, initial soil water content and height of divergence barrier, and HYDRUS model was adopted. By measuring soil water flux from seepage face in a two-dimensional model and comparing it with applied flux in a one-dimensional model at the same depth, the collection efficiency was obtained. Three soil textures including sandy loam, loam and silt were considered, and the values of van Genuchten model parameters for test soils were not changed in HYDRUS model. Moreover, irrigation rates ranged from 100 mm to 1000 mm, and height of divergence barrier ranged from 0 cm to 70 cm. Two initial soil water contents (i.e. 0.15 and 0.35 cm3/cm3) and two soil evaporation rates (i.e. 0.2 and 0.5 cm/d) were adopted. According to the results, the collection efficiency of ZTL without divergence barrier (ZTL0) was low due to lateral diversion of water above the seepage face. As for the ZTL0 under 1000 mm irrigation rates, the collection efficiencies were 0~11%, 5%~13% and 6%~12% in the sandy loam, loam and silt soil, respectively. Due to the fact that more water was accumulated above the seepage face, the measured soil water flux increased as the divergence barrier was installed. However, the height of divergence barrier was reduced with the increase of irrigation rates as well as the decrease of water holding ability of soil and soil evaporation rates. When the height of divergence barrier was less than 20 cm and irrigation rate reached 1000 mm under the condition of 0.35 cm3/cm3 initial soil water content and 0.2 cm/d soil evaporation rate, the collection efficiency of ZTLd was increased to 50%. Thus, coarse-textured soils, divergence barrier, low soil evaporation rate and high irrigation rates were preferred so as to measure water flux rate accurately by ZTLd. High initial soil water content (0.35 cm3/cm3) would lead to low collection efficiency of ZTLd in sandy loam, and collection efficiency of ZTL at a certain burial depth might not be suitable for other depths. According to the assumption of the study, all simulations were based on homogeneous soil without consideration of preferential flow, thus there was no effect of size on the collection efficiency. In conclusion, the results of this research can exert significance to the improvement of ZTL. ©, 2015, Chinese Society of Agricultural Machinery. All right reserved. Source

Zhang S.,Anhui University of Science and Technology | Zhang S.,China Agricultural University | Zhang S.,Key Laboratory of Arable Land Conservation North China | Zhang S.,Key Laboratory of Land Quality | And 10 more authors.
Intelligent Automation and Soft Computing

High-resolution soil texture maps are essential for land-use planning and other activities related to forestry, agriculture and environment protection. The objective of the article was to find suitable methods for predicting soil texture through comprehensive comparison of different prediction methods (e.g., univariate and multivariate methods) by completely taking account of its characteristics as composition data with the same auxiliary information. This article, taking elevation as auxiliary variable, predicted the soil texture using univariate [ordinary kriging (OK)] and multivariate [i.e. regression kriging (RK), simple kriging with locally varying means (SKlm), and cokriging (COK)] methods. Soil texture was transformed by symmetry log ratio (SLR) to meet the requirements of the spatial interpolation for the compositional data. The root mean squared errors (RMSE), the relative improvement (RI) values of RMSE and Aitchison's distance (DA) were utilized to assess the accuracies of different prediction methods. The mean squared deviation ratio (MSDR) was used to assess the goodness of fit of the theoretical estimate of error. The results indicated that according to RMSE and MSDR, the SKlm, COK and RK methods were more appropriate for spatial prediction of sand, clay and silt, respectively. The RI value reached to 22.68% with the SKlm method for clay, 8.24% with the RK method for sand, and 22.49% with the COK method for silt. A scatter plot of DA for the OK method versus DA for the SKlm method, the COK and RK methods showed that predictions obtained with the SKlm method were more accurate than those obtained with the OK, COK and RK methods. By comprehensively considering of values of RMSE, MSDR, RI and DA, SKlm method was more suitable for spatial prediction of soil texture. Effects of auxiliary variable on spatial prediction accuracy of soil texture changed with different prediction methods and types of soil particles. © 2013 TSI® Press. Source

Shi J.,China Agricultural University | Shi J.,Key Laboratory of Plant Soil Interactions | Shi J.,Key Laboratory of Arable Land Conservation North China | Ben-Gal A.,Israel Agricultural Research Organization | And 5 more authors.
Plant and Soil

Background and aims: Michaelis-Menten (MM) kinetics and a physical-mathematical (PM) model are the popular approaches to describe root N uptake (RNU). This study aimed to examine RNU and compare the two model approaches. Methods: A hydroponic experiment (Exp. 1) investigated the effects of root length, root N mass, transpiration, plant age and solution N concentration on RNU of wheat (Triticum aestivum L. cv. Jingdong 8). The two models were applied to simulate the RNU and soil N dynamics in a soil-wheat system (Exp. 2), and the results were compared to the measured data. Results: Under the hydroponic conditions, RNU was better correlated with root N mass and transpiration than root length. The influences of solution N concentration on RNU rate per root length (MM1) and RNU rate per root N mass (MM2) were described well with MM kinetics. The kinetic parameters for MM1 changed with plant age but the parameters for MM2 were not age dependant. The description of RNU with the PM model was also independent of plant age, and was more reliable when the RNU factor decreased as a power function with the solution N concentration (PM2) than an assumed constant (PM1). In Exp. 2, the root mean squared errors between the simulated and measured soil solution N concentration and the relative errors between the simulated and measured N uptake mass for MM kinetics were much larger than those for the PM model. Conclusions: Both the MM and PM models successfully described RNU under the hydroponic conditions, but the PM model (especially PM2) was more reliable than the MM model in the soil-wheat system. © 2012 Springer Science+Business Media B.V. Source

Shi J.,China Agricultural University | Shi J.,Key Laboratory of Plant Soil Interactions | Shi J.,Key Laboratory of Arable Land Conservation North China | Li S.,China Agricultural University | And 6 more authors.
Journal of Hydrology

Governed by atmospheric demand, soil water conditions and plant characteristics, plant water status is dynamic, complex, and fundamental to efficient agricultural water management. To explore a centralized signal for the evaluation of plant water status based on soil water status, two greenhouse experiments investigating the effect of the relative distribution between soil water and roots on wheat and rice were conducted. Due to the significant offset between the distributions of soil water and roots, wheat receiving subsurface irrigation suffered more from drought than wheat under surface irrigation, even when the arithmetic averaged soil water content (SWC) in the root zone was higher. A significant relationship was found between the plant water deficit index (PWDI) and the root-weighted (rather than the arithmetic) average SWC over root zone. The traditional soil-based approach for the estimation of PWDI was improved by replacing the arithmetic averaged SWC with the root-weighted SWC to take the effect of the relative distribution between soil water and roots into consideration. These results should be beneficial for scheduling irrigation, as well as for evaluating plant water consumption and root density profile. © 2014 Elsevier B.V. Source

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