Ammonium Bicarbonate Toxicity root injury occurred from within few hours to several weeks in solution culture tests with citrus, avocado, and soybeans

A. Wallace, M. 1. Biely, and K. C. Bhan

The ammonium source of nitrogen presence of nitrate. Such injury occurred bicarbonate effect could be the result of is often considered less desirable than in about three weeks. the hydroxyl ion. Results were inconclu- other nitrogen sources for some plants. Roots of citrus and soybean seedlings sive. Nitrate is believed-by many people- were injured much in the same manner Since a large portion of the nitrogen to be superior to ammonium nitrogen as were avocado roots, but the injury did fertilizer used in California is ammonic. for citrus, especially under acid soil con- not occur quite so rapidly, nor was there it is of considerable importance to ascer- ditions. injury with a combination of bicar- tain if these effects obtain in the field, Workers in Florida showed recently bonato and nitrate. particularly on alkaline or calcareous that poor growth in citrus with am- Bicarbonate concentrations of 5 m.e. soils where bicarbonates are always monium nitrogen could largely be over- -milliequivalents-per liter or less pro- present. Preliminary results with soil come by raising the pH-relative acidity- duced relatively little toxicity while those tests indicate that there could be some alkalinity-of the nutrient medium to 10 and above produced considerable problem, especially since a toxic effect about 6. toxicity. Likewise the lower ammonium can be pronounced in avocado within It was reasoned that if ammonium ni- concentration, the less the toxicity. hours. trogen were less toxic at pH 6 than at pH Whrn ammonium ni trogen i9 appl i id 4 it might be even less toxic if bicar- Dry Weights of Roots of Soybeans to neutral. alkaline, or calcareous soils, bonate were present and if the pH were Treatment Wt. in sramr nitrifying bacteria convert it to nitrate above 7. The hypothesis involved the ~ ~~ ~ ~~~~~ nitrogen. This process is rapid and es- fixation of the bicarbonate into organic ammonium-N pH 4 ...... 1.5 sentially complete in a iew days. It is a ammonium-N pH 6 ...... 1.7 acids which in turn would be combined ammonium-N pH 7 ...... ,._.3.5 safety mechanism that could prevent am- with the ammonia to form amino acids ammonium-N-bicarbonate pH 8.5. . 1.1 monium bicarbonate toxicity. If soil has and thus provide a means of rendering nitrate N-pH 4 ...... , ...... 4.0 been fumigated or sterilized, however, nitrate N-pH 6 . . . . , ...... 3.9 ammonia nontoxic. The treatment, how- nitrification may be very slow and am- ever, proved to be almost lethal to- the nitrate N-pH 7 ...... , . . 3.5 nitrate N-bicarbonate pH 8.5. . . . 4.0 monia application to soils containing bi- plants. carbonates may be injurious for some crops. Control plants in which nitrate or ani- Root Injury monium nitrogen was maintained and A. Yallare is Associate Professor of Horti- cultural Science, University of Celijornia, Los Avocado roots were severely injured in which changes werr made often Angeles. in solution culturc by ainmoniurri bicar- enough to keep microbial activity at a M. I. Biely is Research Assistant in Horti- honale within 72 hours and by urea with rninimum indicated that the combination ruliuml Science, University of Calijornia, I.os bicarbonate in about seben days. They of ammonia and bicarbonate was neces- Angeles. were visibly injured by ammonium sul- sary to produce the toxicity. heither K. C. Rlian is Research A.wistrrnt in Horti- fate in the presence of calcium carbonate, alone caused it. cultural Science, University 01 Calijornia, Los also in solution culture. in atwut two A number of plants were groMn in nu- A ngdes. weeks. Actually avocado roots were in- trient solutions with ammonium hy- The above progress report is Lased on Re- jured somewhat by bicarbonate in the droxide to determine if the ammonium search Project iYo. 8.51.

PONDEROSA measured by lateral root growth-while green and the roots as turgid and as firm. stock lifted on November 1 did, October Howeber, some rapid method of measur- Continued from preceding pagr 15 and November 1 are not necessarily ing the physiological activity-perhaps age may he closely associated with a critical dates. Weather conditions might gas exchange or reserve food mcasurc- failure to achieve physiological harden- be such that stock lifted on Octoher 15 nients-may provide the answer. ing or readiness before being placed in would be physiologically hardened and Although thcse studies indicate that storage. If this be true, some of the fall- would storc well. Similarly the seed col- early fall lifting and storage may produce stored Mt. Shasta stock, in contrast to lection zone might he correlated with sur- seedlings that are certain to die, they also the Oakdale stock, would have been in a vival and lateral root elongation one indicate that seedling stock lifted and poor physiological condition-perhaps year but not the next. Certainly critical stored later in the year has a good chance even close to death-when delivered to dates can be expecled to differ at each of of survival. the planting site the following spring. the widely separated forest nurseries in ____ Edward C. Stone is Associate Professor oi Since the weather varies from one year the state. Forertry, linrversity of California, Berhela to the next, there is a good chance that The physiological rendition of a seed- Gilbert H. Schubert is Reyearch Forester, the physiological condition of the seed- ling can not be determined by inspection. California Foreyt and Range Experiment Sta- ling at a specified date will not be the Stock lifted on October 1 appears thr tion, U. S. Forest Service, Berkeley. same each year. Although stock lifted same after storage as stock lifted in No- The above progress report is based on Re- on Octoher 15 did not store well-as vember or December; the needles are as Yearch Project No. 1577.

12 CALIFORNIA AGRICULTURE, MARCH, 1959