TERCEIRÂ REUNIÄO BRASILEIRA CIENCIA DO SOLO

136 ANAIS DA TERCEIRA RETJNIÂO BRASILEIRA DE CIÊNCIA DO SOLO
3. Nesta experiência, foi notada uma diminuiçâo de teor de nitratos
em dezembro, que foge ao critério anterior. Admitiu-se comocausa,
a lavagem, bem como a absorçâo intensa dos nitratos do solopelo
mato que cresce. Pode-se explicar, por êsse fenômeno, a falta de
reacao das adubaçoes nitrogenadas minerais, preconizando-se o parcelamènto
do adubo para esta época. Contudo, esta experiência de
variabilidade de nitratos nâo leva a resultados definitivos, pois indica
apenas possibilidade de se resolver o problema de adubaçoes nitrogenadas
minerais no Estado de S. Paulo.
4. A experiência efetuada nâo permite que se aceite uma ascençâo
de sais nas épocas de sêca no Estado, porque nâo houve enriquecimento
de NO3~~ nesses periodos.
5. Existem associadas perdas de NO3~ com as chuvas, porém.
0 fenômeno nâo pôde ser medido quantitativamente.
SUMMARY
From the study of the variation of nitrates in Terra Roxa Misturada
Soil the following conclusion may be drawn:
1. The nitrates content of this soil, show a periodicity correlated,
with the different seasons of the year. This seems to hold for the
greater part of S. Paulo solis, which must have the same periodicity
of the general uniformity of their climate, with minor exceptions.
2. As nitrification proceeds at a higher rate in hot and wet.
seasons (September-May) than in sold and dry ones (May-September),,
nitrates accumulate in the soil during the first period and desapear
in the second. However there appear to be an exception to the above
rule, when it was found a decrease of nitrates in December. This
may be due either to the leaching by rain or from the absorption by
weeds at the time growing in the experimental field. Since nitric
and ammonium nitrogen fertilizers do not generaly yield good results
in S. Paulo, it is logic to assign the decrease of nitrogen content to
the leaching of the soil, although this work do not permit conclusive
explanation about nitrogen fertilizers.
3. This study does not support the theory of the possible uprising
of salts during dry months in the soil since it was found nitrates
to man tain the same level in the soil during these months.
4. Although the author was able to associate losses of nitrates
with mm of rainfall, he was unable to determine this correlation.
quantitatively.
LITERATURA CITADA
1 — BATHAM, H. N. e L. S. NIGAM — Periodicity of the nitrate content of
Soils. Soil Sei. 29:181-190. 1930.
2 — COSTA VERDADE, F. — Dosagem dos nitratos pelo método do âcido fenoldisulfônico.
Apresentado à II Reuniäo Brasileira de Ciência do Solo
e em publicaçao.
3 — DEMOLON, A. e E. BASTISSE — Results of Lysimeter Experiments. Soil Sei.
46:1-7. 1938.
4 — GOWDA, R. N. — Nitrates and nitrification in field soils. Soil Sei.
77:333-342. 1924.
5 — HALL, T. D. — Nitrification in some South African Soils. Sil Sei. XII:
301-363. 1921.
6 — HALL, T. D.>— Nitrification in some South African Soils. Part II. Soil
Sei. 18:219-235. 1924.
7 — SACHS, W. H. — Effect of cultivation on Moisture and nitrate of field.
soil. Univ. of Arkansas Agric. Exp. Sta. Bul. 205.
8 — SMITH, J. B. — Distribuition of nitrates in three layer of fallow Soil-
Soil Sei. 26:347-350. 1928.