ISSN:
1573-5036
Keywords:
dry matter
;
field capacity
;
growth function
;
nitrogen uptake
;
rooting
;
sowing date
;
thermal time
;
wheat
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract The quantities,Y, of nitrogen taken up, and dry matter produced, at various times during the growth of six winter wheat crops at Rothamsted were shown to be related to thermal time,x, based on soil temperature, by a simple equation $$Y = (A^{ - 1/n} + \exp ( - kx))^{ - n} $$ whereA is the ultimate maximum ofY, n a shape factor andk a rate constant that is related toA andn throughx′, the inflexion point of the function. The value ofn was 1.5 for both N uptake and dry matter. The value ofA for N uptake,A N , was well described by a multiple regression on sowing data,t s , expressed as the number of days after August 31st, and rainfall,R Apr , in the April before harvest, but no such regression could be found for the value ofA for dry matter,A D . The rate constants,k N andk D , for N-uptake and dry-matter production respectively, could be related to the date of sowing and the weather through the corresponding inflexion points,x′ N andx′ D . Highly significant regressions were found, forx′ N on the time,t sf , between sowing and the return of the soil to field capacity and forx′ D on the reciprocal oft s . The function was used to generate N uptake curves from values ofA N andk N (obtained fromx′ N ) given by inserting the appropriate values ofR Apr ,t s andt sf in the regressions. These fitted measured N uptakes satisfactorily for the six crops used to obtain the regressions, and four grown subsequently, at Rothamsted, and also for six crops at Woburn. Values ofA D had to be set arbitrarily because no regression had been found to predict them, but using these arbitrary values in the function gave dry matter curves that fitted the measurements satisfactorily for all ten Rothamsted crops and two of the Woburn crops. Tests for seasonal and site effects showed thatA N was influenced more by differences between the two sites than by seasonal differences other than those inR Apr , whereasA D was strongly influenced by these seasonal differencess and very little by those between the sites.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02371030
Permalink
