204 
Journal of Agricultural Research 
Vol. IX, No. 7 
it is shown that the nitrification of green manure, especially the legumes, 
proceeds very rapidly. If green manures are incorporated with the soil 
at the proper stage of maturity, it would seem that some increase in nitric 
nitrogen may be expected during the first seven days and that a large 
percentage of the nitrogen contained in the crop will be converted into 
nitrates within 30 days. Early spring would seem to be the season when 
it is most important to have an abundant supply of available nitrogen in 
Citrus soils. It therefore seems inadvisable to allow the cover crop to 
develop until late spring, as it not only robs the tree of its nitrogen supply 
at a critical season but as the crop becomes more mature the nitrogen 
which it contains is converted into nitrates more slowly after it is plowed 
down. Even if a cover crop is not grown, the winter rains may carry the 
nitrate below the feeding roots of the trees. The rapidity of nitrification 
in the early spring would therefore seem to be of special importance with 
Citrus crops, as the nitrate content of Citrus lands is likely to be very low 
at that time. 
The results presented above also indicate that the growth of cover crops 
may materially assist in maintaining the total nitrogen content of the 
soils. Under favorable conditions it would seem that the nitrogen 
gained by cover crops may more than pay for the additional cost in 
operation. They may also save much nitrogen from leaching away during 
the winter season. 
In the above tables it is shown that, when 1 per cent of dried blood is 
added to soils, much of the nitrogen added is lost. In some cases less than 
50 per cent of the nitrogen added could be recovered after six weeks' in¬ 
cubation. When taken from the incubator, the soils frequently gave off 
a strong odor of ammonia, and it is believed that much or possibly all of 
the loss occurred through the volatilization of ammonia. It is recognized 
that the determinations of the ammonia content of the soils to which 1 
per cent of dried blood was added do not show the quantity of ammonia 
produced but rather the ammonia remaining in the soil at the time the 
analyses were made. Determinations of nitrites were not made, except 
in a few instances; but these few determinations were sufficient to show 
that considerable quantities of nitrites sometimes accumulated in these 
soils following the addition of 1 per cent of dried blood. As the reduc¬ 
tion method was used in determining the nitric nitrogen, it is likely that 
some of the nitrogen recorded as nitrates may have been present as 
nitrites. 
EFFECT OF FURROW IRRIGATION ON THE DISTRIBUTION OF NITRIC 
NITROGEN IN SOILS 
In the irrigation of land many methods of applying the water are now 
in use; but, as a rule, the furrow system is employed in the irrigation of 
orchards, small fruits, root crops, and vegetables. In the irrigation of 
orchards the furrows may vary from 4 to 9 inches in depth, and the number 
of furrows run between adjacent tree rows may vary from 2 to 6. The 
