Sequential estimation of forage dry matter in situ under rapidly changing conditions

Abstract

In rapidly changing conditions repeated calibration of the pasture disc meter is necessary for reasonably accurate estimates of standing forage. Estimates of dry matter yield determined from the disc height of the meter depend on many factors, mainly disc height but also the moisture and fibre contents of the herbage and the degree to which it has been trampled. Daily calibration of the disc meter will automatically take care of these factors but this takes time. Five other methods for describing the changes in dry matter yield with time are discussed: two are multiple regressions with dry mass dependent on disc height, moisture and fibre content and a dummy variate for factors such as trampling and fouling. The use of a multiple regression, which is less laborious than repeated calibration, gave a reasonably accurate estimation of the dry matter yield and time relationship in rapidly changing conditions.

Uittreksel

In snel veranderende omstandighede is dit noodsaaklik om die skyfweiveldmeter herhaaldelik te kalibreer om redelike ramingx van staande weidingsopbrengs te verkry. Ramings met die skyf‐weiveldmeter van dröe materiaal opbrengs is afhanklik van bate faktore, vernaamlik skyfhoogte maar ook vog‐ en veselinhoud van die welding en die mate van vertrapping daarvan. As die skyf‐weiveldmeter daagliks gekallbreer word, sal dit outomaties hierdie faktore in aanmerking neem maar dit is tydsrowend. Vyf ander metodes vir die beskrywing van die verandering in drömateriaalopbrengs word bespreek: twee is meervoudige regressiebepalings met dröe massa as afhanklik van skyfhoogte, vog‐ en veselinhoud en ‘n fopveranderlike soos vertrapping en bemesting. Die gebruik van meervoudige regressiebepalings wat minder werksaam is as die herhaalde kalibrering van die skyf‐weiveldmeter, het dröemateriaalopbrengs redelik noukeurig beraam soos dit in snel veranderende omstandighede gewissel het.

Notes

Extracts from a thesis by the senior author to be submitted for an M.Sc. Agric. degree at the University of Natal.