## Abstract

Soil heat flux (G) is an important component of evapotranspiration (ET) modeling, especially for estimating ET values for hourly or shorter periods. In this study, meteorological and agronomic measurements were made at Kimberly, Idaho, with the purpose of establishing empirical relationships to estimate G for alfalfa and clipped tall fescue grass. For both plant surfaces, good linear correlation was found for most days between the averages of the 20-min net radiation (R_{n}) and G values for a given day. However, when the soil surface was wet, after rain or irrigation, the relationship was subject to hysteresis problems. The linear relationship between G and R_{n} for alfalfa also changed with plant canopy height (h), and an equation was derived to estimate G from R_{n} and h (r^{2} = 0.88). This equation fitted measured G data much better than two other commonly used models (Allen et al., 1996; Clothier et al., 1986). For tall fescue grass, h did not affect the relationship between R_{n} and G, as the grass was clipped weekly resulting in a narrow range of h (0.09 to 0.19 m). A linear equation to estimate G as a function of R_{n} (r^{2} = 0.91) was derived for clipped tall fescue grass, which was found to fit measured data equally well as the model proposed by Allen et al. (1998), but that uses a single equation for both daytime and nighttime instead of two separate equations.

Original language | English (US) |
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Pages (from-to) | 401-409 |

Number of pages | 9 |

Journal | Applied Engineering in Agriculture |

Volume | 21 |

Issue number | 3 |

State | Published - May 2005 |

Externally published | Yes |

## Keywords

- Alfalfa
- Energy balance
- Evapotranspiration (ET)
- Soil heat flux
- Tall fescue grass

## ASJC Scopus subject areas

- Engineering(all)