『Abstract
The distribution and form of P in soil is central to the sustainability
of agricultural practice. This study used sequential fractionation
and 31P nuclear magnetic resonance spectroscopy (31P
NMR) of NaOH-EDTA extracts to examine the influence of pastoral,
native (undisturbed) and forest land use on soil P forms in 5
contrasting soils ranging from a Regosol to a Rendzina in Otago,
New Zealand. Climatic factors likely to influence soil P distribution
were negated by careful site selection. Together with a decrease
in soil organic C (31％), total P decreased in forested soils (mean＝674
mg kg-1) compared to native soils (mean＝784 mg kg-1).
In contrast, the ratio of inorganic to organic P increased (10％)
probably due to mineralization of organic P in forest soils, while
for pasture soils, accumulation of P in inorganic forms due to
P inputs via fertilisers and animal dung was to blame. Investigation
of the organic P forms in NaOH-EDTA extracts of each land use
by 31P NMR indicated that diesters were greatest in
the native soil (4-12％ of total P in spectra), and declined as
a proportion of total P in pasture soils and more so in forest
soils. This was reflected in a decline of the diester to monoester
ratio. However, the ratio was generally greater in forest than
pasture soils and attributed to the labile nature of diesters,
mineralization of monoesters in forest soils, and an increase
in monoesters in pasture soils from inositol phosphates in plant
debris. This effect was pronounced in the Regosol due to sandy
texture and the preferential accumulation of plant debris in coarse
particle size fractions. Due to the depletion of soil P reserves,
forest soils in the area should be followed by pasture and well
managed fertiliser additions before replanting.
Keywords: 31P NMR; Monoesters; Diesters; Organic phosphorus;
Phytate』
1. Introduction
2. Materials and methods
2.1. Soil sites and sampling
2.2. Soil analyses
2.3. 31P NMR
2.4. P fractionation
2.5. Statistical analyses
3. Results and discussion
3.1. Soil phisicochemical properties and phosphorus fractions
3.2. 31P NMR spectroscopic analysis of NaOH-EDTA extracts
3.3. Soil P and land use
4. Conclusions
Acknowledgments
References