34 Experiment Station Bulletin 345 



The Rockingham survey is of a detailed reconnaissance nature, and 

 on a scale of 2 inches equals 1 mile. Enlarged topographic maps are 

 used. The survey is to be made on same legend as the adjacent Strafford 

 County survey (omitting cover or present land use). Soil and slope 

 are to be generalized in rougher and wooded areas; that is, small and 

 insignificant areas of soil and slope are to be included with the dominant 

 condition. In the more extensive rough areas, slope combination may be 

 made, eg., BC, CD, BO. Even in cleared areas, small slope areas differing 

 only in a few degrees from the dominant slope may be included, espec- 

 ially when the use is not affected. Erosion symbols are eliminated in 

 forested areas. Three classes of erosion are used: 1. slight; 2. moderate; 

 3. severe, with symbols for small areas which cannot be separated on 

 scale of map. 



The Podzol group of soil may be eliminated from the legend except 

 for the small areas found in the northwestern part of the county where 

 the Blue Hills Range extends into Rockingham County. (Coop. U. S. 

 Soil Survey) (W. H. Coates, later C. L. W. Swaxson, G. P. Percival) 



Influence of Soil Texture, Soil Moisture, and 

 Soil Aeration upon Growth of Plants 



During the winter of 1940-41 potatoes were grown in the green- 

 house in top soils representing three widely separated textures and three 

 soil series. Buxton clay, Paxton fine sandy loam, and Merrimack loamy 

 fine sand were all air dried and sieved into various size fractions. Two 

 moistures were arbitrarily chosen so that each soil fraction could be held 

 at two different percentages of pore space. Sixty per cent saturation and 

 ninety per cent of field capacity were selected. Total yields of tubers 

 were found to be the easiest and most reliable indication of the effects 

 of these treatments. 



Under these conditions it was found that in general the finer the 

 texture, the greater the yield. This same relationship seems to hold also 

 when the plants are not grown at optimum moisture and when the pore 

 space relationships are different, provided the soils are compared from 

 a similar position on the moisture-yield curve. 



From this work it appeared that the control of soil moisture at 

 definite levels by the usual methods was subject to some error. For in- 

 stance, per cent saturation is usually determined by saturation of the soil 

 from the bottom of the containers in which the plants are to be grown. 

 It was shown that this method was not accurate enough when comparing 

 different soil types because varying amounts of air were trapped in the 

 soil. 



lor the winter of 1941-42 control of this error was attempted in 

 the following way. Total air space was obtained by packing a known 

 weight of soil to a definite volume. Moisture levels at different per- 

 centages of saturation were calculated from the apparent and real specific 

 gravity instead of by saturation from the bottom. In addition, com- 

 pensation was made for the growth of tops and tubers by a gradual in- 

 crease in the water added. 



Three soil types were tested, giving a range of textures: Buxton 

 clay, Newmarket fine sandy loam, and Merrimack loamv fine sand. The 



