COMPOSITION OF PASTURE GRASS 5 



(3) There was a low average phosphorus content in the herbage from all 

 series, falling below all but two of even the poorer values reported from other parts 

 of the world, which have been included in Table 1 for purposes of comparison. A 

 few scattered samples had a phosphorus content above .25 per cent, but the ma- 

 jority of the samples were under .2 per cent. 



Orr'^ in his review of the subject points out that a good pasture will contain 

 approximately .7 per cent of lime and .3 per cent of phosphorus. Review of 

 the available data indicates that about .15 per cent of phosphorus in the herbage 

 is the lower limit of safety. Below that point the deficiency may seriously limit 

 the value of the pasture for grazing purposes, while below .1 per cent mineral 

 deficiency diseases become prevalent. 



It would seem, therefore, that many of these Massachusetts pastures are border- 

 ing on a deficiency of phosphorus, if not actually over the danger line. This 

 statement is particularly applicable to the lighter soils toward the end of the graz- 

 ing season, especially if there has been a period of drought. Note especially in this 

 connection the September values for the samples from Colrain fine sandy loam 

 and for most of the samples taken in Hampshire County. 



One direct result of drought is to lower the moisture content of pasture grasses. 

 In these samples correlation of this lowered moisture content with a lowered phos- 

 phorus content was very evident. The average moisture content of samples con- 

 taining less than .2 per cent of phosphorus was 51.2 per cent, while for those con- 

 taining .2 per cent or more of that element the average moisture content was 60.8 

 per cent. This correlation bears out the observation of Orr that "the percentage of 

 phosphorus tends to decrease with drought." A similar correlation was noted be- 

 tween moisture content and protein content. Samples below 15 per cent of protein 

 averaged 46.9 per cent of moisture; those over 15 per cent of protein averaged 61.1 

 per cent of moisture. 



Results of Partial Analyses of Some of the Pasture Soils 

 Mention has been made of the fact that samples of the surface soil were taken 

 from a majority of the pastures visited. Twenty of these samples have been util- 

 ized to ascertain possible differences in the acidity of the various soil types, and 

 also to see if there was any correlation between the content of available phosphorus 

 in the soil and the phosphorus content of the herbage.'* 



The data indicate that these soils contained in almost all cases a goorl proportion 

 of fine material and were only moderately acid. The Stockbridge soils showed the 

 influence of their limestone origin in a somewhat higher pH (closer to neutrality) 

 than any of the others. With certain exceptions to be noted, there was little or 

 no correlation between the available phosphorus in the soil and the phosphorus 

 content of the grass growing on it. The exceptions are the afore-mentioned Stock- 

 bridge series of soils and certain scattered samples with high values, viz. : a Glouces- 

 ter loam from Brimfield, a Becket loam from Sandisfiekl, and a Peru loam from 

 Chester. 



The values for the Stockbridge series are reasonably constant and also relatively 

 high, due possibly to the influence of lime in fixing the phosphorus in relatively 



^Orr, J. B., Loc. cit. 



*The hydrogen ion concentration of ttie soils was determined by means of a Leeds and Nortlirup 

 potentiometer, using a quinhydrone electrode. Available phosphorus was determined by the method 

 of Truog. (Jour. Amer. Soc. Agron. 22:874, 1930.) 



