The influence of crop canopy on evapotranspiration and crop coefficient of beans (Phaseolus vulgaris L.)

doi:10.1016/S0378-3774(00)00150-5

Agricultural Water Management

Volume 49, Issue 3, 1 August 2001, Pages 211-224

https://doi.org/10.1016/S0378-3774(00)00150-5 Get rights and content

Abstract

Experiments were conducted to investigate the effect of crop development on evapotranspiration and yield of beans (Phaseolus vulgaris L.) at the Instituto Agronômico (IAC), Campinas, State of São Paulo, Brazil, during the dry season of 1994. A completely randomized design was carried out with three population density treatments and four replications. The treatments were: (a) crop sown in evapotranspirometers at a density of 50 plants m⁻², and thereafter thinned to 25 plants m⁻², when the canopy achieved full ground cover; (b) crop sown with population densities of 14 and 28 plants m⁻² in an irrigated field. Crop growth was evaluated considering dry matter (DM), vegetative ground cover (GC%) and leaf area index (LAI). These parameters were successfully related to basal crop coefficient (k_cb) and crop coefficient (k_c), demonstrating the strong dependence of both coefficients on canopy development. A simulation study was carried out and showed that k_cb based on LAI would allow good estimates of water use for different plant density populations in the field.

Introduction

Irrigation water management aims to provide sufficient water to replenish depleted soil water in time to avoid physiological water stress in the growing plants. Hence, a good estimation of daily evapotranspiration (E_t) is an essential information for an efficient and effective irrigation scheduling.

Crop coefficients (k_c) are commonly used to determine actual water needs for a particular crop from estimates or measurements of a potential or reference evapotranspiration (E_t0). The derivation and use of the crop coefficient are given by $k_{c} = E_{t} E_{t0}$

The FAO (Allen et al., 1998) has presented an updated procedure for computing reference and crop evapotranspiration from meteorological data and crop coefficient. These guidelines advise the use of the basal crop coefficient approach (Wright, 1982) as a more precise method to determine daily water consumption by plants. The components of k_c are obtained from the following equation: $k_{c} =k_{cb} k_{a} +k_{s}$ where k_cb is a basal crop coefficient representing the condition when soil evaporation is minimal, but the availability of soil water within the root zone does not limit plant growth or transpiration, k_a the coefficient dependent upon available soil moisture, and k_s the coefficient to adjust for increased surface soil evaporation which occurs after rain or irrigation (Allen et al., 1998, Wright, 1982).

Basal crop curves have been empirically derived by some authors in a time scale as percentage time from planting to effective cover and days after effective cover (Wright, 1982). Nevertheless, weather, tillage practices, soil, water management, and plant growth remarkably influence any time-based crop curve. These factors restrict its transferability to another place or even year-to-year, and lead to crop curves that represent only an historical record.

Correlation of crop coefficients to indexes such as accumulated degree-growing days or heat units have been used by some authors (Sammis et al., 1985, Amos et al., 1989, Nielsen and Hinkle, 1996) to reduce the effects of year-to-year climatic variations on crop development and water consumption. However, these relationships have not always provided improvement as pointed out in Wright (1985).

The basal crop coefficient is mainly related to transpiration (Allen et al., 1998), so developing a functional relationship to k_cb, which is dependent on the crop development rather than on some average conditions based on time or growing-degree-day, and incorporating a plant growth model may be useful to provide a better transferability of crop coefficients (Ritchie and Johnson, 1990).

The main goal of this research was to determine the relationship between the crop coefficient to leaf area index (LAI) and ground cover (GC%), and to investigate their use on irrigation management under field condition.

Section snippets

Material and methods

This study was carried out at the Experimental Station of the Núcleo Experimental de Campinas (NEC) of Instituto Agronômico (IAC), county of Campinas, State of São Paulo, Brazil, located in the tropics, 22°52′S, 47°04′W, at an altitude of 600 m above mean sea level.

The soil is an oxisoil, known as Latossolo Roxo, clay texture (61% clay), naturally well drained, with water content upper limit (field capacity) 0.342 m³ m⁻³, lower limit (wilting point) 0.232 m³ m⁻³, and water-holding capacity

General crop growth and yield

The population density treatments and water management adopted in the present study induced strong differences in the seasonal trend in GC%, LAI, and accumulated DM, as shown in Fig. 2, Fig. 3, throughout the season. The adjusted curves relating LAI, GC%, and DM as a function of time for all treatments are presented in Table 1.

The seasonal trend in crop development parameter values was not proportional to the differences in plant population. Effective cover (80% GC) was attained on 45 DAE at 28

Conclusion

The k_c and k_cb for bean plants were successfully related to LAI and GC%, demonstrating their strong dependence on canopy size.

The partitioning of k_c and an adjusted relation of k_cb as a function of LAI, obtained from only 20 days measurements in a high population density and in an evapotranspirometer study, allowed a good estimation of water use in an irrigation field with two different plant densities.

The work pointed out the need of improving relationships concerning the effects of limiting

Acknowledgements

The authors are grateful to the FAEP-UNICAMP (Fundo de Apoio ao Ensino e Pesquisa da Universidade Estadual de Campinas) and IAC (Instituto Agronômico) for providing financial and physical facilities for carrying out the present study.

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The influence of crop canopy on evapotranspiration and crop coefficient of beans (Phaseolus vulgaris L.)

Abstract

Introduction

Section snippets

Material and methods

General crop growth and yield

Conclusion

Acknowledgements

Agric. For. Meteorol.

Agric. Water Manage.

Fraction of thermal units as the base for an evapotranspiration crop coefficient curve for corn

Agron. J.

Maximum leaf diffusive conductance in vascular plants

Photosynthetica