Sample collection
A total of 750 soil cores were collected in June 1989 at the 15
NPP study sites. The NPP study has 3 sites in each of 5 vegetation
zones (Mesquite, Grassland, Playa, Creosotebush, and Tarbush),
with the three sites representing a range in biomass (sites with
low, medium, and high biomass). All sites are in the Jornada Basin
LTER site approximately 40 km NNE of Las Cruces, NM.. At each of
the 15 NPP study sites, cores were collected beneath the shrub
canopy, and between shrubs at 5 depths (0-10, 10-20, 20-40, 40-60,
60-100 cm), in 5 directions (In buffer zone just outside NPP plots
North, South, East, West, and Center of NPP plot) Samples were
analyzed for pH, CaCO3, NaHCO3-extractable P, KCl-extractable NH4
and NO3, total kjeldahl N, Saturation extract cations, and
DTPA-extractable micronutrients. Percent organic carbon was
sampled at all directions only at the three grassland sites and
only at 0-10cm and 10-20cm depth; one site per vegetation type was
sampled at all depths for CU (center-under) location only.
Nutrient and chemical analyses
Soil samples were air-dryed in a glasshouse and ground to pass a
2-mm seive. Total N (and TP) was digested by Kjeldahl digestion
block techniques (Bremner and Mulvaney, 1982). Digest NH4-N was
analysed using an automated salicylate procedure (Technicon
Industrial Method No. 329-74W/B).
Inorganic N (NH4-N and NO3 + NO2-N) was extracted with 2M KCl
(Keeney and Nelson, 1982). Ammonium-N in the extracts was analyzed
colorimetrically (indophenol blue) in an automated procedure
(Technicon Industrial Method No. 154-71) and NO3 + NO2-N was
measured by an automated Cd reduction colorimetric procedure
(Technicon Industrial Method No. 100- 70W/).
Available P was analyzed as NaHCO3-extractable (PO4) P (Olsen and
Sommers, 1982).
Percent H2O was determined using the gravimetric method (wt
water/wt dry soil).
Soluble cations (K, Na, Ca, Mg) were extracted using saturation
extract methods (Rhoades 1982, Richards 1954), and analyzed as
following: EC read on Yellow Springs Instruments (YSI) model 32
conductance meter Na, Ca, Mg read on Perkin Elmer ICP/6500
(inductively coupled plasma) K read on Perkin Elmer Model 5000
Atomic Absorption Spectrophotometer using emission mode, acetylene
flame
DTPA extractable micronutrients (Zn, Mn, Cu,. and Fe) were
extracted using DTPA extraction method (Lindsay and Norvell,
1978), and analyzed using inductively coupled plasma atomic
emmission spectrophotometry.
Organic C was determined using a modified Mebius method (J.C.
Yeomans and J.M. Bremner, 1988).
References
Bremner, J.M., and C.S. Mulvaney. 1982. Nitrogen–Total. In : A. L.
Page, R. H. Miller, and D. R. Keeney (eds.). Methods of soil
analysis. Chemical and microbiological properties, Part 2, 2nd
Edn. Agronomy 9 (2):595-624. Am. Soc. of Agron., Madison, Wis.
Technicon Industrial Method No. 329-74W/B:
TKN–>NH4——>ammonia-salicylate complex
TP—>PO4——->phosphomolybdenum complex
Keeney, D.R. and D.W. Nelson. 1982. Nitrogen–Inorganic forms. In:
A. L. Page, R. H. Miller, and D. R. Keeney (eds.). Methods of soil
analysis. Chemical and microbiological properties, part 2, 2nd
Edn. Agronomy 9 (2):643-698. Am. Soc. of Agron., Madison, Wis.
Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. In: A. L. Page,
R. H. Miller, and D. R. Keeney (eds.). Methods of soil analysis.
Chemical and microbiological properties, Part 2, 2nd Edn. Agronomy
9 (2): 403-430. Am. Soc. of Agron., Madison, Wis.
Technicon Industrial Method No. 94-70W/B PO4 (orthophosphate)
phosphomolybdenum complex
Rhoades, J. D. 1982. Soluble Salts. In: A. L. Page, R. H. Miller,
and D. R. Keeney (eds). Methods of Soil Analysis, Chemical and
Microbiological Properties, Part 2, 2nd Edn. Agronomy 9(2):
167-179. American Society of Agronomy, Madison, Wis.
Richards, L.A, ed. 1954. Diagnosis and improvement of saline and
alkali soils. Chapter 2. Determination of the properties of saline
and alkali soils. pg. 7-33. USDA Handbook #60.
Lindsay, W.L. and W. A. Norvell. 1978. Development of a DTPA soil
test for zinc, iron, manganese, and copper. Soil Sci. Soc. Am. J.
42:421-428.
Yeomans, J.C. and J.M. Bremner, 1988. A Rapid and Precise Method
for Routine Determination of Organic Carbon in Soil. Dept of
Agron., Iowa State Univ, Ames Iowa 50011. In: Commun. in Soil Sci.
Plant Anal., 19(13), 1467-1476 (1988).