Jm. Choi et Pv. Nelson, DEVELOPING A SLOW-RELEASE NITROGEN-FERTILIZER FROM ORGANIC SOURCES .1. USING NONVIABLE BACTERIA, Journal of the American Society for Horticultural Science, 121(4), 1996, pp. 629-633
Mineralization of N from nonviable cells of Brevibacterium lactofermen
tum (Okumura et al.) mixed into soilless substrate in elution columns
occurred largely during the first 5 weeks with a peak between 2 and 3
weeks. Over a 12-week period, 73% of the total N was recovered in the
eluent. To prolong the period of N release to meet the requirements of
a slow-release fertilizer, the bacterium was bonded to kraft lignin,
a polyphenolic substance highly resistant to degradation. To retard mi
neralization further, the bacterium-lignin mixture was reacted with fo
rmaldehyde to form amino cross-links within and between protein chains
. Bonding to lignin was undesirable because N release occurred during
the same period as from the bacteria unbound to lignin and the total a
mount of N recovered was reduced to only 42%, Cross-linking with forma
ldehyde was less desirable since N was released mainly during the firs
t 4 weeks with a peak during the first elution (0 time) and the total
amount of N released was even lower than for the bacterium-lignin mixt
ure, Additions of urea to the latter reaction did not satisfactorily i
mprove subsequent N mineralization. In a second set of treatments lign
in was withheld and the bacterium was reacted with weights of formalde
hyde (a.i.) equivalent to 0.1%, 0.5%, 1.0%, 5.0%, and 10.0% of the dry
weight of bacterium, Formaldehyde quantities less than or equal to 1.
0% either had no effect or lowered the mineralization of N without alt
ering time of release, Five percent and 10% formaldehyde successfully
reduced release of N during the first 4 weeks and increased it thereaf
ter. The best rate was 5%, In this treatment N was released from week
2 through the end of the test (12 weeks). Peak release occurred at 6 w
eeks. This resulting N source, while not a stand alone product, does h
ave a slow-release property that could lend itself to use in combinati
on with other slow-release N sources.