Ap. Mallarino et M. Ulhaq, TOPSOIL AND SUBSOIL POTASSIUM AS AFFECTED BY LONG-TERM POTASSIUM FERTILIZATION OF CORN-SOYBEAN ROTATIONS, Communications in soil science and plant analysis, 28(17-18), 1997, pp. 1537-1547
Long-term potassium (K) fertilization practices are likely to affect t
he K content of soils. This study assessed the effect of long-term K f
ertilization strategies for corn (Zea mays L.) and soybean [Glycine ma
x (L.) Merr.] rotations on extractable K in the soil profile of a majo
r Iowa soil type at two locations. The soil type was a Webster fine-lo
amy, mixed, mesic, Typic Haplaquoll at both sites. Soil samples were c
ollected from the 0-15, 15-30, 30-60, and 60-90 cm depths after 17 yea
rs (Site 1) or 19 years (Site 2) of K fertilization with combinations
of two initial rates and four annual rates. The initial rates were 0 a
nd 1,344 or 1,120 kg K ha(-1) at Site 1 and 2, respectively, and the a
nnual rates ranged from 0 to 100 kg K ha(-1). Samples were analyzed fo
r ammonium acetate-extractable K (STK) and nitric acid (HNO3)-extracta
ble nonexchangeable K (HNO3-K). Concentrations of STK and HNO3-K in th
e top 0-15 cm soil layer at the two sites were higher for the high ini
tial K rates and were linearly related with the annual K rate. Results
for the subsoil layers varied between sites and extractants. At Site
1, annual rates of 30 kg K ha(-1) or higher resulted in a relative acc
umulation of HNO3-K in the 15-30 cm layer. At Site 2, these rates resu
lted in relative accumulations of STK in the 30-60 cm layer and of HNO
3-K in the 60-90 cm layer, but with relative depletions of STK in the
15-30 and 60-90 cm layers. Thus, use of one extractant may not always
be sufficient to evaluate cropping and fertilization effects on subsoi
l K. Long-term K fertilization of corn and soybean rotations affected
extractable K of both the topsoil and subsoil. The effects on subsoil
K, however, were smaller compared with effects on the topsoil and vari
ed markedly between sites, subsoil layers, and extractants.