
TY  - JOUR
A1  - Robertson, FA 
A1  - Myers, RJK 
A1  - Saffigna, PG 
T1  - Distribution of carbon and nitrogen in a long-term cropping system and permanent pasture system
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 1993
VL  - 44
IS  - 6
SP  - 1323
EP  - 1336
KW  - carbon;nitrogen;total soil N;organic C;microbial biomass;plant dry matter
UR  - https://doi.org/10.1071/AR9931323 
N2  - Nitrogen (N) limitation to productivity of sown perennial grass pastures on the brigalow lands of S.E. Queensland contrasts with adequate N supply to annual crops grown on the same soil. In order to understand this anomaly, the distribution of N and carbon (C) under permanent green panic pasture and under continuous cropping with grain sorghum was compared in an 18 month field study. Total soil N and organic C (0-10 cm) were, respectively, 0.37 and 3.20% under green panic and 0.23 and 2.31% under sorghum. Soil microbial biomass (0-28 cm) contained 246 kg N and 1490 kg C ha-1 under green panic and 147 kg N and 744 kg C ha-1 under sorghum. Enhanced microbial growth under pasture was attributed to the continuous input of available C from surface litter and roots. The C/N ratio of pasture residues was high (greater than 50) and conducive to immobilization of N. Availability of N under pasture was further reduced by approximately 50% of plant N being immobilized in standing dead tissue. Under sorghum, the microbial biomass was well supplied with N, but was limited by C availability. The soil under sorghum received a single large C input when crop residues were returned after harvest. The differences in N availability, and hence productivity, of these soils under cropping and permanent pasture were due primarily to differences in the timing and quality of C inputs. 
ER  -

