SOIL EXHAUSTION AND ROTATION OF CROPS. 



195 



what the height of the stubble was ; probably it was rather short, 

 as straw is too valuable in most parts of Prussia to be left on the 

 ground. These figures were obtained to throw light on what 

 happens under the circumstances that prevail in the culture at 

 Proskau. We want a similar work done to throw light on what 

 happens under our circumstances, and this work should be repeat- 

 ed several years, so that we shall arrive* at average figures that 

 can be fully depended upon. Referring to the table, you have of 

 rye stubble and roots, 3400 lbs.; of barley, 1515 lbs.; of oats, 

 2200 lbs.; of wheat, 2240 lbs., of red clover, 6580 lbs.; of buck- 

 wheat, 1630 lbs.; of peas, 2400 lbs.; of lupine, 2800 lbs. 



You see at once the bearing of these figures. You see that 

 when you have got your clover hay off the field, there remains, 

 within ten inches of the surface, twice as much vegetable matter 

 as is necessary to go into the next rye crop, and three times as 

 much as is necessary to go into the next wheat crop. That helps 

 to explain why clover is a good preparation for these crops. 

 Look at the column headed " Nitrogen." In rye, we have 62 ; in 

 wheat, 22 ; in clover, 180 lbs. Take lime. In rye, 69 ; in clover, 

 246; and so on. What I want to show mainly by this table is 

 expressed in the first column of figures — the amount of vegetable 

 matter remaining in the roots. 



Here we have another set of figures which refer somewhat in 

 detail to two of our standard crops — Rye and Clover. 



Roots. 



Top 



Rye, before heading. 



" headed 



" in bloom 



" ripe 



Clover, before bud.. . 



" in bud 



" in blossom .. . 

 " ripe 



av. length. 



6 inches. 



8 " 



8 " 



8 " 

 18 •' 

 16 " 

 14£ " 

 15 " 



weight. 



50 



106 



143 



253 



56 



94 



106 



147 



Roots. 



weight. 

 30 

 23 

 24 

 19 

 35 

 50 

 45 

 99 



Ratio of 

 Root to Top. 



10: 17 



10: 45 



10: 59 



10: 136 



10: 16 



10: 19 



10: 23 



10: 15 



In tfiis experiment, due to Heiden, a mass of soil one foot wide, 

 five feet long, and four feet in depth, was enclosed in boards, then 

 lifted out and the roots removed by careful picking and washing. 

 The average length of the roots was noted, and the total weight 

 of roots arid tops ascertained. This was done, as the table 

 shows, at several different periods of growth. 



You see from the second column that the roots of rye at the 

 time of heading had an average length of eight inches, and did 



