New Zealand Journal of Crop and Horticultural Science abstracts
Green-manure impacts on nitrogen availability to organic sweetcorn (Zea
mays)
J. A. Hanly
P. E. H. Gregg
Fertilizer and Lime Research Centre (PN 432)
Institute of Natural Resources
Massey University
Private Bag 11 222
Palmerston North, New Zealand
email: j.a.hanly@massey.ac.nz
Abstract Two field experiments were conducted in the
Gisborne region of New Zealand to assess the effectiveness of four winter
green-manure crops (lupin, mustard/lupin mix, mustard, and annual ryegrass)
for improving the short-term nitrogen (N) availability of soils growing organic
sweetcorn (Zea mays). Average soil mineral (0-15 cm) N in the control
treatment (bare soil winter fallow) plots, measured at the time of sweetcorn
emergence (late November 1997), was 50.4 kg N ha-1 at Site A and
81.3 kg N ha-1 at Site B. Compared with the control (bare soil
fallow) treatment, soil incorporation of the lupin and mustard/lupin mix
treatments significantly increased soil mineral N by 30-45% at both trial
sites at sweetcorn emergence. In contrast, the ryegrass treatment reduced
soil mineral N levels by 33-43% at both sites. These treatment effects were
related to green-manure crop N concentrations just before soil incorporation.
Sweetcorn N accumulation at final harvest was also significantly increased
by soil incorporation of the lupin and mustard/lupin mix treatments and significantly
reduced by the ryegrass treatment. Average sweetcorn ear yields in the control
treatment plots at maturity were 16 t ha-1 at Site A and 18 t
ha-1 at Site B. However, ryegrass treatment significantly reduced
sweetcorn ear yields by 64% at Site A and 48% at Site B, which was likely
to have been caused by the lower soil mineral N levels attributed to soil
incorporation of the ryegrass treatment. Although the lupin and mustard/lupin
mix treatments increased soil N availability and uptake by sweetcorn, these
treatments did not significantly improve sweetcorn ear yield. The lack of
yield response was attributed to soil moisture limitations, which occurred
in the latter part of the season and were likely to have restricted yield
potential.
Keywords sweetcorn yield; organic certification; green-manure
crops; residue incorporation; lupin; mustard; annual ryegrass; soil mineral
nitrogen
H03095; Received 14 October 2003; accepted 17 June 2004Online publication
date 9 September 2004
New Zealand Journal of Crop and Horticultural Science, 2004, Vol. 32:
295-307
0014-0671/04/3203-0295 $7.00 © The Royal Society of New Zealand
2004
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