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Are you making the most of the Nitrogen available in
your soil?
Tessa Mills 1 , Celine Repussard 2 , Emily Morrison 3 , Siva Sivakumaran 1 , Steve Green 1 , Ian McIvor 1
1 The Horticulture and Food Research Institute of New Zealand (HortResearch), P. B. 11030, Palmerston North, NZ,
2 Ecole Nationale d’Ingenieurs des Travaux Agricoles de Clermont-Ferrand, Option Agronomie et Productions Végétales, Site de
Marmilhat, BP 35, 63370 Lempdes, France
3 Palmerston North Girls High School, Fitzherbert Avenue, Palmerston North
INTRODUCTION
Nitrogen (N) is an essential plant nutrient
and is generally applied at relatively high
rates in kiwifruit compared with other
perennial horticultural crops. High levels
of plant-available N encourage strong
vegetative growth and may impair fruit
quality in kiwifruit. This, coupled with
the potential increase in leaching l
osses under a high N loading, justifi es
the need for research to improve
our understanding of how N can be
managed for maximum benefi t without
environmental compromise.
Since June 2004, the Sustainable Land Use
Team from HortResearch has carried out
fi eld experiments on a high-producing
Hort16A property in the Te Puke region.
The research is funded by the Sustainable
Farming Fund (SFF) administered by MAF,
and it has focused on the impact of either
increased, or reduced, application of N on
the nitrogen economy of the vines.
Treatments were based on the grower’s
current rates of fertiliser use, with Control
being equivalent to approximately 145kg
N/ha/y, Zero-N had no additional inputs of
N fertiliser, and High-N had twice the current
commercial rate (approximately 295kg N/
ha/y). All other nutrients were applied at
current commercial levels. A detailed
description of the SFF trial can be found in
the May/June 2007 edition of the New
Zealand Kiwifruit Journal (Mills et al. 2007).
Table 1 outlines application of all other
elements over the three years of the trial.
Product applied Kg/ha 2004 Kg/ha 2005 Kg/ha 2006
Lime 1250 1000
Muriate of potash 250 154 150
Sulphate of potash 725 761 756
Cal mag 192 173
Super phosphate 250
Triple super phosphate 300 225
Ferrous sulphate 20 20 20
Granular boron 3 3 5
Calcium ammonium nitrate 415 477 435
Kieserite 225 190
Nitrobor 174 155 150
Gypsum 250
Dolomite 500
Compost 5000
Table 1. The application of all other elements during the 3 years of this trial.
During the three-year trial period, the Zero-N
treatment vines showed reduced leaf and
fruit N levels compared with both Control
and High-N vines. The Zero-N treatment
had signifi cantly reduced vegetative growth
every year, yet fruit size was reduced (by cf.
10g) in just one year, and that was only
when compared with the High-N treatment.
Despite having no N fertiliser applied for
three seasons, and consistently high
cropping levels (16,000-17,000 trays per
ha) which we may expect would deplete
soil reserves, the Zero-N vines continued to
perform well. Fruit set for the 2007-2008
season was similar between all three
treatments.
The deep pumice-derived ash soil at the
trial site has the potential to provide
signifi cant amounts of plant-available N
(Mills et al. 2007). Indeed, the reserves of
mineral N were such that the Zero-N vines
retained their reproductive capacity (i.e.
return bloom, fruit size) albeit with a
reduction in vegetative growth. Results from
our fi eld trials suggest that although the
total mineral N content in the soil is much
lower in the Zero-N vines cf. the High-N
vines, a large amount of N is still available to
the vines, through mineralisation of soil
organic matter which releases plant available
mineral N from the organic N pool.
NZ KIWIFRUIT JOURNAL JANUARY / FEBRUARY 2008
29