STUDIES ON SOIL TEST CORRELATION, CALIBRATION AND INTERPRETATION FOR PHOSPHORUS FERTILIZER RECOMMENDATION ON MAIZE (Zea mays L.)
STUDIES ON SOIL TEST CORRELATION, CALIBRATION AND INTERPRETATION FOR PHOSPHORUS FERTILIZER RECOMMENDATION ON MAIZE (Zea mays L.)
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Date
1997-12
Authors
NTO, EMERUCHE KALU
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Abstract
The study was carried out in the southern Guinea savanna zone of Nigeria to
develop a soil testing programme which leads to the establishment of a rational basis
for phosphorus fertilizer recommendations to crops. To achieve this, correlation studies
to determine the best extractant of available phosphorus, and calibration studies to
develop site specific fertilizer recommendation practices were carried out.
Thirty-six surface soil samples collected across Benue, Plateau and parts of Kogi
States were used for the correlation studies. Eight soil test methods, Mehlich 1,
Mehlich 2, Bray 1, Bray 2, Olsen's, Modified Mehlich 1, Mississippi, and AB-DTPA
were used to extract phosphorus from the soils. Pot experiments were set up in the
greenhouse using maize as the test crop. Two treatments, P0 without phosphorus, and
P1, with adequate amount of phosphorus, were used. Maize was grown for 35 days.
Forage dry matter yields and phosphorus uptake were determined.
Ten sites were selected for the field fertilizer rate studies which were carried
out for two cropping seasons, 1988 and 1989. Six phosphorus fertilizer rates, 0, 20,
40, 60, 80 and 100 kg P2Os/ha, were used. Surface soil samples were collected before
maize planting and fertilizer application. Available phosphorus was extracted with the
eight soil test methods.
The results showed that each soil test method extracted a wide range of
phosphorus from the soils. The effectiveness of the methods in solubilising quantities
of phosphorus from the soils was Bray 2 > Olsen's > Mehlich 2 > Modified Mehlich
1 > Bray 1 > Mehlich 1 > AB-DTPA > Mississippi, with a mean extractable
phosphorus of 5.54, 5.47, 4.50, 4.0, 3.57, 2.86, 1.74 and 1.22 mg kg-1, respectively.
The herbage dry matter yields of maize at P0 varied among the soils and ranged
from 1.03 to 13.72 g/pot. Analysis of variance showed that the yields varied
significantly at the 0.1 % probability level with a high coefficient of variation of 21.1 %.
The phosphorus uptake at P0 also varied very significantly with the soils and ranged
from 1.29 to 24.0 mg/pot.
Actual yield, relative yield, actual yield increase and phosphorus uptake were
used to evaluate the effectiveness of the soil test methods. In general, the precision of
prediction was relative yield > actual yield > phosphorus uptake > actual yield
increase. The effectiveness of the extractants varied with the yield parameters. In all,
Mehlich 1, Modified Mehlich 1 and Bray 1 were the best predictors, in that order.
From the correlation studies it was found that all the eight soil test methods
were suitable for solubilising available phosphorus from these soils. However, Mehlich
1 which was the most precise and effective and the least influenced by soil properties
is recommended for soil testing in the southern Guinea savanna.
The results of the field fertilizer rate studies showed that maize grain yields
varied from treatment to treatment in each site, from site to site for each treatment, and
from year to year for each site-treatment. In general, the soils in all the 19 site-years
responded significantly to phosphorus fertilization although the degree of response
varied from site to site and year to year.
The critical levels of extractable phosphorus were determined by both CateNelson
graphical and analysis of variance methods. The results were as follows:
Mehlich 1, 7.25 and 7.29 mg kg1, Mehlich 2, 13.0 and 13.20 mg kg1, Bray 1, 8.0 and
7.83 mg kg"1, Bray 2, 8.0 and 6.76 mg kg', Olsen's, 7.25 and 6.94 mg kg1, Modified
Mehlich 1, 6.75 and 6.36 mg kg1, Mississippi, 1.20 and 1.12 mg kg1, and AB-DTPA,
2.70 and 2.60 mg kg-1, for the two methods, respectively.
The Mitscherlich-Bray equation, Log(A-y) = Log A-C,b, and its expanded
form, Log(A-y) = LogA - C,b - Cx, were used for calibrating the responses of maize
to phosphorus fertilization. The correlation factors, C,, obtained for Mehlich 1,
Mehlich 2, Bray 1, Bray 2, Olsen's, Modified Mehlich 1, Mississippi and AB-DTPA
soil tests were 0.047, 0.040, 0.056, 0.048, 0.069, 0.045, 0.243 and 0.156,
respectively. Also the efficiency factor, C, for band applied phosphorus fertilizer was
calculated as 0.014. Based on the Mitscherlich-Bray relationships and a graphical
approach, arbitrary values of percent sufficiencies, y, of 10 to 93% which cover a full
range of soil deficiencies, and corresponding soil test values, b, phosphorus fertilizer
recommendations, x, were obtained. Calibration curves and tables were produced for
the various soil test methods for use in interpreting soil test data to farmers.
Description
A thesis submitted to the Postgraduate School, Ahmadu Bello University, Zaria, in
partial fulfillment for the award of the Degree of Doctor of Philosophy in Soil Science.
Department of Soil Science
Faculty of Agriculture
Ahmadu Bello University
Zaria, Nigeria
Keywords
SOIL,, TEST,, CORRELATION,, CALIBRATION,, INTERPRETATION,, PHOSPHORUS,, FERTILIZER,, RECOMMENDATION, MAIZE (Zea mays L.)