Twenty 6 x 6 m plots with a 3-meter buffer zone were established on
the Jornada Basin CDRCC in 1986. Five plots each were randomly
assigned to one of four treatments: (1) chlordane amendment (100ml Al
(Active Ingredients) per 10,000 ml) to exclude microarthropods, (2)
water (irrigation 6 mm per week), (3) water (6 mm per week) plus
chlordane amendment (100 ml Al per 10,000 ml) and (4) control, no
treatment. In May, randomly selected fluffgrass (_Dasyochloa
pulchella_) rhizospheres from each plot were selected for nitrogen
mineralization analysis.
Net mineralizable N was estimated using batch incubation procedures
for 0, 2, 4, and 8-week incubation periods. Soil subsamples (25g) were
incubated at 35 C in 50-mL plastic vials covered with 0.0125 mm
polyethylene film and seal with rubber bands to reduce moisture loss.
Moisture content was adjusted to 10% water content by weight at weekly
intervals by injecting deionized water through a small hole in the
film with a syringe. Subsamples were removed for inorganic N (NH4-N
and NO3 +NO2-N) determination following 2, 4, and 8-week incubation
periods. Inorganic N was extracted by placing 10 g of soil into
polyethylene bottles containing 100 ml of 2.0 Molar KCL + PMA (to
prevent growth by bacteria and fungi). Samples were shaken 30 times,
set for 24 hours, and then filtered. NH4 -N was measured by an
automated salicylate procedure (Wall and Gehrke, 1975) an NO3 + NO2-N
by an automated cadmium reduction procedure (Henriksen and
Selmer-Olsen 1970). Net N mineralization was calculated at the net
change in N occurring from the beginning to the end of each
incubation.
Gravimetric soil moisture was determined for all the samples used for
inorganic N and nitrogen mineralization potential. Ten grams of
well-mixed soil from each sample were oven-dried for 48 hours at 105
C, and reweighed.