J. Vos, Split nitrogen application in potato: effects on accumulation of nitrogen and dry matter in the crop and on the soil nitrogen budget, J AGR SCI, 133, 1999, pp. 263-274
In four field experiments, the effects of single nitrogen (N) applications
at planting on yield and nitrogen uptake of potato (Solanum tuberosum L.) w
as compared with two or three split applications. The total amount of N app
lied was an experimental factor in three of the experiments. In two experim
ents, sequential observations were made during the growing season. Generall
y, splitting applications (up to 58 days after emergence) did not affect dr
y matter (DM) yield at maturity and tended to result in slightly lower DM c
oncentration of tubers, whereas it slightly improved the utilization of nit
rogen. Maximum haulm dry weight and N content were lower when less nitrogen
was applied during the first 50 days after emergence (DAE). The crops abso
rbed little extra nitrogen after 60 DAE (except when three applications wer
e given). Soil mineral N (0-60 cm) during the first month reflected the pat
tern of N application with values up to 27 g/m(2) N. After 60 DAE, soil min
eral N was always around 2-5 g/m(2). The efficiency of N utilization, i.e.
the ratio of the N content of the crop to total N available (initial soil m
ineral N + deposition + net mineralization) was 0.45 for unfertilized contr
ols. The utilization of fertilizer N (i.e. the apparent N recovery) was gen
erally somewhat improved by split applications, but declined with the total
amount of N applied (range 0.48-0.72). N utilization and its complement, p
ossible N loss, were similar for both experiments with sequential observati
ons. Separate analysis of the movement of Br- indicated that some nitrate c
an be washed below 60 cm soil depth due to dispersion during rainfall. The
current study showed that the time when N application can be adjusted to me
et estimated requirements extends to (at least) 60 days after emergence. Th
at period of time can be exploited to match the N application to the actual
crop requirement as it changes during that period.