Water as a Limiting Factor in the Growth of Sweet Clover (M. Alba)

Abstract

Summary1. Sweet clover (white) will apparently live in the loam soils employed in the present trial with as little moisture as 9 percent of the dry weight of the soil in which it grows. On the clay soil employed in this series sweet clover appeared to cease growth when the percentage of water on the basis of the dry soil approached 11 percent as a minimum. It is thus indicated that even under conditions otherwise identical variations in soil type may produce some variation in the amounts of water necessary for growth of sweet clover. The observation that soil type, regardless of other conditions may furnish a factor influencing water requirement is in substantial agreement with other investigators. Pages 259, 261, 272, 273.2. When the factor of soil type was equalized, it was observed that as the percentage content of moisture in soil was increased, the total amount of water utilized by the plants increased. With increase of moisture content by degrees, in soil from 9 percent, to a maximum of 32 percent, the total water used increased regularly from 6.6 kilos to 79 kilos. Thus in general, sweet clover plants can make some growth with very limited moisture, but if water is available to them they can adapt themselves to use it. Pages 261, 273.3. It is also apparent that the average production of dry matter per plant increases with the total amount of water utilized. Page 261.4. One chief factor in the increase of dry matter of sweet clover produced with the increase of available water was the increase in height of main stems; the extreme height of plant (main stem) was found to increase, with the increase of water available, up to 22 percent of the dry weight of soil. When the percentage of available water was still further increased the corresponding increase in dry matter apparently was produced not by increase in extreme height but by increase in number of stems and branches. Such was the means by which sweet clover plants adapted their manner of growth to the increases in water. Page 273.5. Also in regard to the manner of growth of sweet clover plants as affected by increases in amount of water; it appeared that the average weight of the leaves of plants increased, and that the mean area per leaf increased with increase in the amount of moisture available. This statement is based on measurements made in 1918. Pages 273, 275. 6. It appeared that the average actual water requirement (as indicated by the ratio of grams water used to grams of air-dry tops produced) increased with an increase in the amount of the water available, up to 18 percent of the weight of soil, possibly beyond. In short sweet clover will not only utilize more total water within limits when it becomes available, but also will utilize more water per gram of dry matter up to a maximum. Pages 272, 273.7. The present researches indicate that as an average on all soils the water requirement for sweet clover varies according to the percentage of water available, from 675 to 789. Page 275.8. These figures for water requirement as determined agree substantially with those furnished by Briggs and Shantz, for conditions at Akron, Colorado, they having secured a water requirement of 770. Page 294.9. Sweet clover may be said to have an average water equirement, as compared to plants listed in general; tumble weed with 277 and millet with 310 are among the lowest and brome grass, with 1016, highest in respect to water requirement. Page 294. 10. Previous to beginning the present researches, South Dakota Experiment Station published Bulletin 151, Trials with Sweet Clover as a Field Crop, which indeed may have been the earliest bulletin published giving results with growing, harvesting and feeding the plant in question as a harvested crop. At the beginning of the present researches it was intended to get quantitative information about the capacity of the sweet clover plant to adapt itself to a wide range of cropping conditions. It becomes more apparent that sweet clover possesses that range of adaptability. In spite of some limitations as a crop-plant it may well increase in importance as a farm crop, in South Dakota and throughout the world