174 



MISCELLANEOUS PUBLICATION 1271. U.S. DEPARTMENT OF AGRICULTURE 



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~30- 

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o 40- 









50- 



95T.C.I 



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- Saltbush 





+ Saltbush 



Significance 



of difference 



(P) 



N.S 



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N-S 



N.S 



08 06 OJ 02 0.2 0.4 0£ 0.8 



CHANGE IN MOISTURE CONTENT (gm /cm 2 ) 



■ ' i i i 



80 40 40 80 



ROOTS OF SALTBUSH (% of total by weight) 



Figube 7. — Soil moisture use in adjacent sites with and 

 without bladder saltbush (Atriplex vesicaria) at Em- 

 met "Vale, 49 km. N.N.W. of Deniliquin, N.S.W. (fig. 1) 

 over the 33 days after November 19, 1970. Average 

 initial moisture contents for the depths 0-7.6, 7.6-23, 

 23-38, and 38-54 cm. were 16.9, 20.2, 22.6, and 25 per- 

 cent; 15.4, 19.5, 23.0, and 26.3 percent of soil ovendry 

 weight for the sites with and without saltbush, respec- 

 tively. Average short-wave radiation over the period 

 was 676.2 cal./cm. 2 /day. The water-use was equivalent 

 to 1,009 cal./cm. 2 and 568 cal./cm. 2 in the saltbush and 

 no saltbush sites, respectively (taking 1 g. water = 590 

 cal./cm. 2 ). Light falls of rain over the period of mea- 

 surement (totalling 1.24 cm.) have not been included 

 in the calculations. The percentage of saltbush roots 

 with depth was calculated from data of Jones and 

 Hodgkinson (31). 



lands of N.S.W., where one-and-a-half to one- 

 hundred-fold concentrations occurred, depending 

 on the particular plant nutrient. No similar 

 study appears to have been conducted in the arid 

 and semiarid rangelands, although Lange (35) 

 had noted a concentration of sheep fecal pellets 

 of greater than 4:1 between sites at 183 and 1,600 

 m. from a watering point. Evidence of the con- 

 centration of nutrients is also commonplace in 

 the shade of trees, the corners of paddocks, or 

 near watering points by the presence of pure 

 stands of reputedly nutrient demanding species 

 such as Sisymbrium erysimoides Desf., S. irio L. 

 and Hordeum leporinum Link (barley grass). 



Removal Of Major Recycling Species 



Variation of organic carbon, nitrogen, and 

 phosphorus, and of chlorides, sodium, potassium, 

 calcium, magnesium, total soluble salts, and con- 



ductivity is known to occur in the soils of many 

 of the rangeland shrub steppe communities (4, 

 30, 33, 50, 51, Marshall and Tupper, unpub- 

 lished). Many of the dominant perennials (Atri- 

 plex spp. and Kochia spp.) accumulate sodium 

 and chloride in their leaves in the field and under 

 glasshouse conditions and some are nutritionally 

 favored by high concentrations of sodium (5, 12, 

 30, 76.) 



These studies have implications for stock inter- 

 actions which result in the elimination of species 

 which predominate in the recycling and spatial 

 transfer of plant nutrients. Jessup (30) showed 

 that concentrations of chloride and total soluble 

 salts under Emneapogon ovenaceus (Lindl.) C. E. 

 Hubbard grassland, which had previously carried 

 the shrub species A. vesicaria and K. astrotricha. 

 were at levels more comparable with the inter- 

 shrub soil rather than the higher concentrations 

 below the shrubs. Charley (14) proposed that the 

 pattern of redistribution of chloride following 

 the destruction of perennial shrubs by grazing 

 is a key factor in the sequence of species domi- 

 nance as grazing intensity increases. Thus, the se- 

 quence of dominance from A. vesicaria to Bassia 

 spp. to Enneapogon sp. with increased grazing 

 pressure is related to a progressive decrease in 

 salinity concentration of the depressions in which 

 the vegetation he was studying grows, and an in- 

 crease in concentration of the surrounding, un- 

 vegetated shelves. Rixon (50, 51) showed that soil 

 from mounds associated with Atriplex vesicaria 

 before its elimination 5 years previously by graz- 

 ing still exceeded soil from intervening areas in 

 its capacity for mineralization of nitrogen but 

 was significantly lower than the capacity of soil 

 from below existing shrubs. 



The emphasis on shrub steppe communities has 

 been intentional because little of relevance has 

 been reported for other Australian rangeland 

 communities with few exceptions (11, 46, 54, 75). 

 Gaps also exist in the understanding of the shrub- 

 steppe patterns perhaps the most noteworthy of 

 which is the comparatively little attention given 

 to soil water movement in the distribution of the 

 soluble anions and cations although associations 

 between the two are evident in the work of Jessup 

 (30) and Jones (33). 



The possibility exists for addition of nitrogen 

 to the rangeland ecosystem by direct fixation by 



