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Field-scale calibration of the PAR Ceptometer and FieldScout CM for real-time estimation of herbage mass and nutritive value of rotationally grazed tropical pasture.

Keyanna C. Peters, Martin P. Hughes and Oral Daley

Martin Hughes

Smart Agricultural Technology



Vol. 2

Leaf area indexLight interceptionChlorophyll indexPrediction model

Destructive sampling method is regarded as the standard approach for evaluating pasture herbage. However, non-destructive methods for managing pastures are rapidly gaining acceptance because they provide faster results that can influence real-time decision-making. The objective of this study was to calibrate the PAR Ceptometer and FieldScout CM as non-destructive tools for real-time prediction of herbage mass and nutritive value, respectively of rotationally grazed pasture. Sixty (60) herbage samples were cut from three (3) rotationally grazed paddocks to determine herbage mass (HM) and nutritive value [crude protein (CP), apparent neutral detergent fiber (aNDF), apparent acid detergent fiber (aADF) and in vitro organic matter digestibility (IVOMD)] after leaf area index (LAI) and light interception (LI) [PAR Ceptometer], sward height (SH) and chlorophyll index (CI) [FieldScout CM] measurements were taken. There were strong positive correlations between sward physical characteristics and CI (r2 = 0.74 to 0.90) and between CI and CP (r2 = 0.81). The LAI and LI accounted for 81 % and 75 % of variability in HM, respectively. The CI accounted for a maximum of 68 % variability of CP. However, concordance correlation coefficient (CCC) of these prediction models were poor. Models with highest prediction accuracy for HM were those with SH (cb= 0.89) and LAI (cb= 0.81). Regression bias was the main sources of error for HM prediction models, while the primary error for CI predicted aNDF (75.4 % MSPE) and IVOMD (95.5 % MSPE) occurred at random. It was concluded that the PAR Ceptometer produced unreliable estimates of HM while the FieldScout CM is capable of producing reliable predictions of aNDF and IVOMD of rotationally grazed mixed Brachiaria arrecta and Digitaria eriantha pastures.



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