New Zealand Journal of Agricultural Research abstracts
Balanced and adequate potassium and phosphorus nutrition
of pasture
J. D. MORTON
L. C. SMITH
K. G. DODDS
AgResearch
Invermay Agricultural Centre
Private Bag 50 034
Mosgiel, New Zealand
W. D. CATTO
Ballance Agri-Nutrients
Private Bag 12 503
Mt Maunganui, New Zealand
Abstract Pasture production responses from applications of
four rates each of potassium (K) (0, 112.5, 225, 450 kg ha-1) and
phosphorus (P) (0, 60, 120, 240 kg ha-1) in a factorial design were
measured in a mowing trial with 60% of clippings returned at a K- and
P-responsive site (54.6 μg K ml-1 and 9 μg Olsen P
ml-1) at Woodlands in Southland, New Zealand over 2 years. There
were large significant responses in total pasture dry matter (DM) production to
K and P. A bivariate Mitscherlich-related equation accounted for 97% of the
variation in measured values of total DM yield, 94-99% of the variation in
ratios of K, P, and nitrogen (N) concentrations in mixed herbage, and 99-100%
of the variation in nutrient ratios in white clover, summed or averaged over 2
years. The fitted equations were used to identify combinations of fertiliser P
and K rates and ratios of K and P concentrations in mixed herbage and clover
that resulted in balanced and adequate nutrition. Two nutrient elements are in
balance when the yield response to one added on its own equals the response to
the other added on its own, both in relation to the maximum yield. Balanced
nutrition in total DM occurred at a K/P ratio of 5.1-7.4 for mixed herbage and
4.2-7.9 for clover, and were highest at higher rates of K and P. For balanced
nutrition at 95% relative yield, K/P ratios were 6.8 for clover and 6.7 for
mixed herbage. Fertiliser K/(K + P) ratios for balanced nutrition increased
from 0.5 for fertiliser expenditure of $50 ha-1 to 0.7-0.8 for
expenditure of $100-200 ha-1. Modelled yield at the fertiliser K/(K
+ P) ratio for balanced nutrition in mixed herbage and clover DM was similar to
maximum modelled yield. Mixed herbage and clover K/P ratios derived from
economically optimal fertiliser K/P ratios were 6.2-6.6 and 5.6-6.7,
respectively. Using N concentration as an internal standard, nutrient adequacy
is defined as the herbage yield with K and P in physiological balance relative
to the maximum yield with K and P in physiological balance and expressed as RY
[KP]. At 95% RY [KP], adequate nutrition was achieved at K/N of 0.77 for mixed
herbage and 0.46 for clover. Overall, the results from the trial reported here
confirm that ratios of nutrient concentrations are useful indicators of
balanced and adequate K and P nutrition for total pasture production. Mixed
herbage or clover nutrient concentrations and ratios were both effective
indicators of balanced and adequate nutrition.
Keywords balanced nutrition; white clover; fertiliser ratio;
potassium; phosphorus; interactions; response surface; economically optimal
nutrient ratios
New Zealand Journal of Agricultural Research, 2001, Vol. 44: 269-277
0028-8233/01/4404-0269 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (614K); (scanned from paper original: notes about this process)
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