Abstract:
This study assessed the impact
of crop diversification within no-till crop
rotations on soil organic carbon and total
nitrogen stocks, as well as on labile (Carbon
and Nitrogen in the particulate organic
matter) and persistent (Carbon and Nitrogen
in the mineral-associated organic matter)
Organic matter fractions. The objective was
to identify practical indicators for monitoring
public policies promoting low carbon
emission agriculture. Field experiment was
conducted in 2014/2015 cropping season
using a complete random block design. Seven
treatments were evaluated: soybean/cotton
(CONTROL); maize/soybean (M/Sb);
soybean/maize+brachiaria (Sb/M+Br);
soybean/millet+brachiaria/crotalaria
spectabiliscotton (Sb/Mt+Br/CrsCt);
soybean/cotton/common beans/millet+
brachiaria (Sb/Ct/Cb/Mt+Br); millet-cotton/
soybean/maize/crotalaria spectabilis (Mt-
Ct/Sb/M/Crs); crotalaria-cotton/soybean/
sorghum+brachiaria/crotalaria ochroleuca+
brachiaria (Cr-Ct/Sb/Sg+Br/Cro+Br).
Sampling was done in May 2020 on an Oxisol
in a neotropical savanna of the Central West
region of Brazil (Capivara Experimental
Research Farm of Embrapa Rice and Beans,
Santo Antônio de Goiás, Goiás State, Brazil).
Treatment comparisons were made after
correction for equivalent soil mass per soil
layer. The C-POM, N-POM, C-MAOM, and
N-MAOM fractions were obtained through
granulometric physical fractionation. Total
SOC and SOC stocks were inadequate
indicators of the impact of crop rotations on
SOC. However, the distribution of C and N
among the soil organic matter (SOM)
fractions (C-POM, N-POM, C-MAOM, and
N-MAOM) was influenced by crop rotations.
Rotations with greater crop diversity,
including gramineae, had higher
concentration of C and N in the particulate
SOC (C-POM and N-POM). Differences in
rotation composition also affected the C to N
ratio, particularly in the POM fraction, which
was higher in rotations involving brachiaria
grass and maize. Most diversified rotations
contributed to maintaining higher C-POM
stocks.
