ecosystem services to and from north american arid ... - Conabio

IV SIMPOSIO INTERNACIONAL DE PASTIZALES
San Luis Potosí, S.L.P. México; 22 al 24 de agosto de 2007
Artículos in extenso
Área temática: Productividad
RELATIONSHIP BETWEEN NORMALIZED DIFFERENCE VEGETATION INDEX
(NDVI) AND FORAGE YIELDS IN MIXED PASTURES
Santillano-Cázares, J. 3 *, J.L. Caddel 1 , D.D. Redfearn 1 , H. Zhang 1 , C.L. Goad 2
1
Professor and Extension Department of Plant and Soil Sciences, Oklahoma State University.
2
Professor Department of Statistics, Oklahoma State University.
3
Professor and Reasearch Facultad de Agronomía de la Universidad Autónoma de San Luis Potosí.
Soledad de Graciano Sánchez, S.L.P., México. Tel.: 444-852-40-53, Ext. 103. santillano64@hotmail.com
ABSTRACT
Mixed pastures are typically highly variable in forage yields both in time and space. For pasture
management and researching activities, obtaining quick, reliable, convenient, and non
destructive estimates of forage yields in pastures would be useful to make informed decisions.
Normalized difference vegetation index (NDVI) is a widely used index that has been used with
encouraging results to estimate grain yields of annual crops like wheat (Tritricum aestivum L.)
and corn (Zea mays L.). In mixed pastures, little information exists concerning the degree of
association between NDVI and forage yield. The objective of this research was to test a handheld
sensor for estimating relative differences of forage yield in mixed grass-legume pastures.
During five seasons, NDVI measurements were collected from five fertilizer treatment strips in
four pastures. Forage yields were measured immediately after scanning. In four of five seasons,
the correlation coefficients (r) were significant but inconsistent. The last two seasons, because of
drought, yields were extremely low and the relations were of opposite sign, negative in the
spring of 2004-2005 (r = - 0.75, P < 0.001) and positive during in the summer (r = 0.98, P <
0.001). We propose that the relationship is simply random under such of low yields.
Contrastingly, in the summer of 2004-2005, when high forage yields were recorded, an r = 0.68
(P < 0.001) was observed, but the correlation substantially increased in the fall of 2005-2006 (r =
0.76, P < 0.001), when forage yields decreased substantially. This evidencing that a probable
loss of sensitivity of NDVI occurred as a result of high forage yields compared to when lower
forage yields were recorded. It was concluded that NDVI is not a reliable estimator of forage
yields in mixed pastures due to a loss of sensitivity under extremes of forage production levels
and because a substantial fraction of the yield is often composed by non green forage, while
NDVI was designed to detect green tissue.
INTRODUCTION
In mixed pastures, besides the complexity of including multiple species, these systems are
typically highly variable in forage yields both in time and space. Obtaining quick, reliable,
convenient, and non destructive estimates of forage yields in pastures would be beneficial to
pasture management and research activities. Spectral reflectance is a tool that has been long
used in the assessment of amount of several plant parameters like biomass and condition of the
vegetation. The principles of the spectral reflectance technology rely on the amount and
composition of light reflected from the vegetation. Vegetative indices result from combining two
or more spectral bands and several indices have been developed to serve different purposes in
the evaluation of different variables of interest of vegetation (Jackson and Huete, 1991).
Although with limitations, NDVI has been reported to correlate with certain physical properties of
the vegetation canopy like leaf area index, vegetation cover, vegetation condition, and biomass
(Carlson and Ripley, 1997). Encouraging results have been obtained using NDVI as a tool to
predict grain yield in early stages of growth of corn (Teal et al., 2006) and winter wheat [Mullen
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