Vijay Shankar

Methods to estimate irrigated reference crop evapotranspiration – a review

Efficient water management of crops requires accurate irrigation scheduling which, in turn, requires the accurate measurement of crop water requirement. Irrigation is applied to replenish depleted moisture for optimum plant growth. Reference evapotranspiration plays an important role for the determination of water requirements for crops and irrigation scheduling. Various models/approaches varying from empirical to physically base distributed are available for the estimation of reference evapotranspiration. Mathematical models are useful tools to estimate the evapotranspiration and water requirement of crops, which is essential information required to design or choose best water management practices. In this paper the most commonly used models/approaches, which are suitable for the estimation of daily water requirement for agricultural crops grown in different agro-climatic regions, are reviewed. Further, an effort has been made to compare the accuracy of various widely used methods under different climatic conditions.

Model for Nonlinear Root Water Uptake Parameter

AbstractAn empirical relationship is developed for the nonlinear root water uptake parameter in the O-R moisture uptake model from easily measurable plant physiological parameters, such as maximum daily transpiration, maximum root depth, and time to attain the maximum transpiration. A nondimensional parameter, termed specific transpiration, that involves the plant physiological parameters is used in this empirical relationship. Data for determining this relationship are obtained by minimizing the deviations between the field observed moisture depletions of 28 crops reported in the literature, and the Richards equation–based numerically simulated soil moisture depletions combined with the moisture uptake model accounting for root water uptake. In addition to cross-validation, field experiments on three Indian crops (maize, Indian mustard, and wheat) are conducted to further validate the proposed empirical relationship. Comparisons of model predictions with field observations of soil moisture profiles and m...

Evaluation of a Nonlinear Root-Water Uptake Model

Soil-water movement due to root-water uptake, is a key process for plant growth and transport of water in the soil plant system. There are different root-water uptake models to determine the extraction rate of soil moisture by roots. The present study examines the performance of different root-water extraction models using available data as well as data generated under controlled conditions. Data pertaining to moisture uptake in respect to two crops: wheat (Triticum aestivum L.) and maize (Zea mays L.) along with soil-water characteristics have been monitored at the Indian Institute of Technology Roorkee, agricultural farm. For this purpose, a numerical model is also formulated by incorporating different moisture extraction terms as sink terms in the Richards equation. A nonlinear root-water uptake model selected as the base model was evaluated for its moisture uptake efficiency. The work establishes the merits of the base model over other extraction terms considered, particularly constant and linear extr...

Evaluation of root water uptake models – a review

Estimation of root water uptake and water movement in plants is crucial to quantify transpiration and hence the water exchange between land surface and atmosphere through plants. Present paper is aimed to illustrate and discuss how mathematical modeling can be used for understanding of plants and, in particular, plant–soil interactions. Soil water movement due to root water uptake is a key process for plant growth and transport of water in the soil plant system. There are different root water uptake models which can be used for estimation of moisture uptake by plants. The accuracy of moisture uptake prediction by plants depends on selection of proper mathematical models. Root uptake models are available in different forms i.e. linear, nonlinear, and exponential. In this paper, a detailed review of the most commonly used models which are suitable for the estimation of moisture uptake by plants in different agro-climatic regions is presented. Further, an effort has been made to compare the performance of different widely used models under controlled condition and future research needs are outlined.

Soil moisture dynamics modeling considering multi-layer root zone

The moisture uptake by plant from soil is a key process for plant growth and movement of water in the soil-plant system. A non-linear root water uptake (RWU) model was developed for a multi-layer crop root zone. The model comprised two parts: (1) model formulation and (2) moisture flow prediction. The developed model was tested for its efficiency in predicting moisture depletion in a non-uniform root zone. A field experiment on wheat (Triticum aestivum) was conducted in the sub-temperate sub-humid agro-climate of Solan, Himachal Pradesh, India. Model-predicted soil moisture parameters, i.e., moisture status at various depths, moisture depletion and soil moisture profile in the root zone, are in good agreement with experiment results. The results of simulation emphasize the utility of the RWU model across different agro-climatic regions. The model can be used for sound irrigation management especially in water-scarce humid, temperate, arid and semi-arid regions and can also be integrated with a water transport equation to predict the solute uptake by plant biomass.

Nondimensional Relationship for Root Water Uptake in Crops

AbstractRoot water uptake is often modeled as a sink term in the Richards equation to account for evapotranspiration losses. The sink term is assumed to be a power law function in the nonlinear root uptake model (O-R model) to account for the decrease in root density and water uptake with depth. In order to extend the O-R model to other crops without requiring detailed and time-consuming experiments, two important dimensionless numbers (specific transpiration, Ts, and specific root water uptake, T*) are identified based on readily available plant parameters. Data for determining the relationship between these numbers are obtained by minimizing the deviations between the field-observed moisture depletions of 28 crops reported in literature and the numerically simulated soil moisture depletions. Field experiments on three Indian crops—maize, Indian mustard, and wheat—are used for validation of the proposed empirical relationship. This relationship shows promise for use in the O-R model for root water uptake...

Evaluation of two irrigation scheduling methodologies for potato (Solanum tuberosum L.) in north-western mid-hills of India

ABSTRACT Water shortage is the prominent limiting factor for agricultural sector in developing countries. The efficient water use is required which helps to obtain effective irrigation schedule for various crops. The present study aims at establishing optimized irrigation schedule for potato, which is a major cash crop in Northern India. Study is conducted in open field plot of Agricultural Experimental Station at National Institute of Technology Hamirpur (India) for Potato during 2013–2016. Irrigation scheduling models based on root water uptake and growing degree days concept are used to workout irrigation schedule for potato in the study. Comparison of field observed and modelled values of percentage moisture depletion in different depths and soil moisture variation at various depths is performed to evaluate the models efficacy in estimating soil moisture extraction by the potato crop for the crop period and replications during study period. Root uptake-based model is found to have better agreement with observed values. The irrigation schedule developed helps in optimal use of irrigation water in water scarce areas.