『Abstract
Accumulated soil P in agricultural soils is a major source of
soluble and particulate forms of P entering water resources and
degrading water quality. However, few research sites are currently
available to evaluate the long-term effects of different cropping
systems and fertility practices on soil inorganic and organic
P accumulation. The objectives of this study were: (1) to compare
soil P fractions in plots on Sanborn Field, which has been cultivated
for 111 years; and (2) to assess the use of standard soil test
P extractants for determining changes in soil P dynamics over
time. A modified sequential P extraction procedure was used to
separate labile and stable inorganic and organic P pools from
surface soils collected on Sanborn Field in 1915, 1938, 1962,
and 1999 from plots in continuous corn, continuous wheat, continuous
timothy, and a corn-wheat-clover rotation amended with either
manufactured fertilizers, horse or dairy manure or receiving no
fertilization since 1888. Additional samples were collected from
a native grass prairie site of a similar soil series to estimate
soil characteristics at Sanborn Field before initial cultivation
in 1888. Observed accumulation of Bray-1 P among fertilizer and
manure treatments was attributed to over-application of P due
to unrealistically high yield goals for each cropping system.
Long-term cultivation of Sanborn Field increased soil bulk density
and lowered soil pH and total organic C compared with native prairie.
Fertilization either by addition of manufactured fertilizer or
manure significantly increased inorganic resin-P and inorganic
NaOH-extractable P. Applications of animal manure also significantly
increased most organic P fractions compared with the unfertilized
treatment. The native prairies had a larger proportion of total
P in organic forms compared with cultivated plots, especially
in organic NaOH-extractable P, but no significant decreases in
either residual or total P were observed due to cultivation. This
study confirms that soil P availability in cropping systems that
are amended with predominantly organic P amendments may differ
from conventional cropping systems relying on manufactured P fertilizers.
however, no direct evidence was found to support the hypothesis
that any individual inorganic or organic soil P fraction has a
better relationship than conventional soil test P extractants
with plant P uptake under contrasting organic and conventional
fertility practices.
Keywords: Sanborn Field; Soil P pools; Cropping systems; Animal
manure; Native prairie』
Introduction
Materials and methods
Soil sample collection from Sanborn Field and Tucker Prairie
Soil analysis
Data analysis
Results and discussion
P fertilization and soil P accumulation
P fractions
Conclusions
Acknowledgements
References
| 方法 | リン画分 | 実用的なリンプール |
| 土壌試料（1.5 g） | ||
|
0.4 gの陰イオン交換樹脂、 16時間振とう、 20 mLの0.5M HCｌで回収されたリン |
樹脂による無機リン（Resin Pi） | 利用可能の（Available） |
|
30 mLの0.05M NaHCO3（炭酸水素塩）（pH 8.5）、 16時間振とう |
炭酸水素塩による無機リンと有機リン（Bicarbonate Pi + Po） | 不安定な（Labile） |
|
30 mLの0.1M NaOH（水酸化ナトリウム）、 16時間振とう |
水酸化ナトリウムによる無機リンと有機リン（NaOH Pi + Po） | ゆっくりした（Slow） |
|
20 mLの0.1M NaOH（超音波処理）、 16時間振とう |
水酸化ナトリウムの超音波処理による無機リンと有機リン（NaOH sonication Pi + Po） | 吸蔵された（Occluded） |
|
30 mLの1.0M HCｌ（塩酸）、 16時間振とう |
塩酸による無機リン（HCl Pi） | 風化可能なl鉱物（Weatherable mineral） |
|
5.0 mLのH2SO4（濃硫酸）による温浸（digestion）、 360℃で3時間 |
残渣リン（Residual P） | 不活性の（Passive） |
※土壌リンの連続抽出法は、Hedley et al.（1982）をBeck and Sanchez（1994）が修正したものを使用。