Abstract. Ammonium sulfate, ammonium carbonate or ammonia gas inhibited water uptake in sugar beet roots whenever the pH was sufficiently high to cause the production of ammonia. When ammonia was removed by aeration, inhibition of the water uptake by roots was rapidly reversed. ATP at 0.2 mm appeared to either wholly or partially prevent the ammon,ia-induced inhibition of water uptake by roots. ATP may be involved in maintaining the structure of water pathways through the root. In roots lacking epidermis, ammonia did not inhibit water uptake by the roots. This may indicate that the site of the inhibition lies within the root epidermis.During a previou,s study we observed that sugar beets grown in the greenhouse or out-of-doors in a nutrient solution (pH 7.6-8.0) using ammonium suilfate as the ni,trogen source wilited severely on h,o,t summer days. Sugar beets ireceiving poitassium nlitraite as a nitrogen soturce sthowed little, if any, wiliting. On ciloudy days or ait night, no difference in wiilting wa's observed between the treatments. lit appeared that amimonia may have been interfering with the movement of water thrrotugh the sugar beeit plant.Several investigators have reported that respiration inhibitor's anid/o,r un!oouplers such as cyanide (2,3,15,16,17,19), aziide (2,13, 19), 2,4-dinitrophen,ol (16), fluoiride (2), i'odoacetate (2), arrsenate (2), phenylurethiane (2), and lack of oxygen (15,20) decrease the movement oif w,alter int'o or oult of coleolptille segmenits, root segments 'or initact roots. Ammonia (NH3) and/or undi ssocia'ted ammonium hydroxide, hereinafter called ammonia, mlay also act as respi,ration inhibitors. AlItschuil et al. (1) showed that treating cotton seed wiitih ammonia inhibited respiration in boith mature and immature seeds. V:nes and Wedd:n,g (24,26) found that ammon.a inhbted resp.rat.on in excised bar'ey roots, garclen bee't di,skq, leaf d.sks of sp:nach antd sugiar beets and garden beet root m:toc'hondr.a. They fouiind that the degree o,f inh'b tion was related to pH, since pH controls the amount of ammon:a present in solutitons contan:ng ammon um ion's (NH,').

Grass tetany, a Mg deficiency of ruminants, accounts for significant economic losses to Western cattlemen during the spring grazing period on Agropyron desertorton. This nutritional deficiency may also occur when ruminants graze other temperate grasses, but the soil-plantanimal factors leading to the problem are not well understood.The objective of this study was to provide definitive data relating seasonal changes in the chemical composition of forage to the occurrence of grass tetany on semiarid•grasslands,The field experiment was established on two calcareous soils where grass tetany had previously occurred. Agropyron desertorum forage was harvested from both sites at regular intervals during the spring tetany period in each of 5 years. The forage samples were analyzed for mineral elements, N, total water-soluble carbohydrates (TWSC), higher fatty acids (HFA), ash alkalinity, and aconi tic acid.High levels of N and HFA, which are known from other studies to reduce Mg availability to the animal, coincided with the occurrence of tetany. The low Mg concentrations measured in the forage probably provided only marginal levels of available Mg to the grazing animals. A rapid increase in the ratio of N/TWSC coincided with the onset of tetany, and may be the primary factor which indirectly decreases Mg availability and precipitates the occurrence of tetany. Although the relationship of the protein/energy imbalance to grass tetany has been suggested previously, as far as the authors are aware this is the first time that N/TWSC values obtained during the growing season have been documented in conjunction with the occurrence of grass tetany.Additional index words: Crested wheatgrass, Hypomagnesemia.

In soils, downward water movement is restricted when finetextured materials are underlain by sand or gravel layers. Water accumulates in arid and semiarid soils at the interface of the fine‐ and coarse‐textured materials and may rarely enter the coarse‐textured materials. Calcium carbonate, silica, and other salts are deposited at or near the top of the sand or gravel layers as water is removed by evapotranspiration. With time, silica, calcium carbonates, and other salts become cemented or indurated, forming calcareous crusts at these interfaces. The sands and gravels are not wet uniformly when water does enter, because it enters relatively small areas. Calcareous concentrations may form in these small, wetted areas and may be seen as calcareous cemented columns surrounded by noncal careous sands or gravels.