Ce. Wilson et al., CHEMICAL ESTIMATION OF NITROGEN MINERALIZATION IN PADDY RICE SOILS .2. COMPARISON TO GREENHOUSE AVAILABILITY INDEXES, Communications in soil science and plant analysis, 25(5-6), 1994, pp. 591-604
A simple nitrogen (N) availability index is needed to improve fertiliz
er recommendations and, thus, reduce the opportunity for over- or unde
r-fertilization of rice (Oryza sativa L.). Consequently, a study was c
onducted to develop a chemical extraction procedure that will estimate
the potentially mineralizable N made available to rice during the gro
wing season. The ammonium-nitrogen (NH4+-N) extracted with 0.05M KMnO4
(potassium permanganate) + 0.5M H2SO4 (sulfuric acid) (acidified KMnO
4), 0.05M K2Cr2O7 (potassium dichromate) + 0.5M H2SO4 (acidified K2Cr2
O7), 1.0M HCI (hydrochloric acid), and 0.5M C2H2O4 (oxalic acid) was c
ompared to total N uptake (TNU) by 'Newbonnet' rice grown under greenh
ouse conditions. Comparisons were also made between distillation of th
e entire soil-extractant Suspension (TOT) and distillation of the supe
rnatant after centrifugation (SUP). Anaerobic incubation for 7, 14, an
d 21 d was also included for comparison. The indices evaluated decreas
ed in ability to predict TNU in the order: anaerobic incubation > acid
ified KMnO4 > acidified K2Cr2O7 = HCI > oxalic acid. Anaerobic incubat
ion was the best index of N availability for rice. The 14-d incubation
predicted TNU (r2 = 0.82*) better than the 7- or 21-d incubation (r2
= 0.71 and 0.65*, respectively). The best chemical index of N availa
bility was oxidation with acidified KMnO4 (r2 = 0.75*). Extraction wi
th HCI (TOT) and acidified K2Cr2O7 (TOT) were similar and extraction w
ith oxalic acid was the least effective method. Pre-incubation of each
soil for 30 d prior to anaerobic incubation did not improve the relat
ionship with TNU by rice in the greenhouse.