We. Jokela et al., IMPROVED PHOSPHORUS RECOMMENDATIONS USING MODIFIED MORGAN PHOSPHORUS AND ALUMINUM SOIL TESTS, Communications in soil science and plant analysis, 29(11-14), 1998, pp. 1739-1749
The need for reliable recommendations for phosphorus (P) application o
n cropland has become increasingly important in recent years with the
need to optimize economic inputs and minimize adverse water quality im
pacts. We used results from a series of recent laboratory and field ex
periments with Vermont and New York soils, combined with those of earl
ier work, to revise state recommendations for P application on field c
rops. Based on results of field and greenhouse studies, we established
a critical value of 4 mg kg(-1) (optimum range of 4.0 to 7.0) using m
odified Morgan extractant [1.25 M ammonium acetate (NH4OAc), pH 4.8] a
s a measure of plant-available P. Aluminum (Al) in the same extractant
(''reactive'' Al) correlated well with the amount of added P needed t
o increase soil test P. Consequently, P rate recommended for soils bel
ow 4 mg kg(-1) is based on a combination of extractable P and Al. With
in the ''Optimum'' range only a low rate of P is recommended. Modified
Morgan P also correlated well with P desorbed into water or calcium c
hloride (CaCl2) solution, suggesting it is a good indicator of the pot
ential for a soil to release P into runoff. These research results sup
port use of modified Morgan-extractable P and Al for P fertilizer reco
mmendations for crop production and water quality purposes in the New
York-New England region of the United States.