Agriculture Reference
In-Depth Information
Fig. 6.6.
The effects of applying liquid 'starter' fertilizer injected below seeds at
sowing on the early seedling growth of onions in a sandy loam soil with a gradient
of available P and of available K. The liquid fertilizer consisted of a mixture of
ammonium phosphate and potassium phosphate, which delivered 375, 980 and 920
mg/m per row of N, P and K, respectively. Extraction, analysis and indexing of soil P
and K levels were performed according to UK recommendations (MAFF, 2000) (from
Stone, 1998. Courtesy of the
Journal of Horticultural Science and Biotechnology
).
attainment of a high Leaf Area Index (LAI), which causes earlier bulb maturity
for the reasons outlined in Fig. 4.33 (Brewster
et al.
, 1992). This tends to lead
to better quality at harvest and less likelihood of non-ripening, 'thick-necked'
bulbs.
Starter fertilizers may enable vegetable crops, including onions, that need
soils of high P and K fertility to yield well and to be grown successfully on soils of
lower P and K status than previously. Maintenance applications of 100-200
kg/ha of P and K are applied annually to many soils to maintain high levels of
plant-available P and K, to counteract the constant tendency for these nutrients
to become fixed in unavailable forms and for the available P and K levels to
stabilize at a lower steady-state concentration (Karpinets and Greenwood,
2003; Karpinets
et al.
, 2004). This is both wasteful of fertilizer and potentially
polluting, particularly if soil of high P and K levels is eroded into waterways,
where it can contribute to eutrophication.
Stone (1998) demonstrated that injection 25 mm below seeds of a liquid
starter fertilizer of ammonium phosphate plus potassium phosphate giving 375,
980 and 920 mg of N, P and K, respectively, per m row (equivalent to 10, 27 and
25 kg/ha N, P and K, respectively) virtually eliminated any effect of soil P or K
fertility on onion seedling growth (see Fig. 6.6). In a further experiment, starter
fertilizer combined with injection of liquid NPK to make a total fertilizer
application of half the recommended rate for onion bulbs, gave a higher yield than
