Agriculture Reference
In-Depth Information
Fig. 6.3.
(a) Relationship between organic N (%) and weight per unit area in dry
matter of onions that were not growth limited by N, as young plants in June (
) and as
bulbs in September (
). The line is the expected relationship for a C
3
species.
(b) Effects of fertilizer N on plant population in June (
●
) and at final harvest in
September (
) on a light loam soil. (c)
Effect of fertilizer N on onion dry weight yield per unit area (
●
), and on mean plant dry weight in June (
) and on mineral N in
the depth ranges (cm) 0-90 (
) for a September harvest of ripe
bulbs on two light loam soils in The Netherlands (right-hand graph is from the same
soil as for graph (b)) (from Greenwood
et al
., 1992. Courtesy of
Fertilizer Research
).
●
), 0-60 (
) and 0-30 (
The critical K concentration behaves similarly to critical N, and the ratio of
critical percentage K:critical percentage N is 0.595 for onion and 0.902 for
leeks (Greenwood and Stone, 1998). The critical percentage P is roughly eight-
to tenfold lower than the critical percentage N, and also declines as crop weight
increases (Greenwood
et al.
, 1980d).
The bulb onion crop presents a considerable challenge to supply nutrient
uptake per unit root length at a sufficiently high rate to permit the maximum
RGR of seedlings and, later, during the main period of bulb growth to supply
sufficient total N from their restricted rooting depth to achieve maximum bulb