This presentation was presented during the 2 Parallel session on Theme 3.2, Managing SOC in: Grasslands and livestock production systems, of the Global Symposium on Soil Organic Carbon that took place in Rome 21-23 March 2017. The presentation was made by Mr. Fernando García-Préchac, from University of Uruguay, in FAO Hq, Rome

1. Long-term effect of different agricultural soil use
and management systems on the organic carbon
content of Uruguay prairie soils (Molisols).
Fernando García-Préchac
Prof. Dept. of Soils and Water
Fac. de Agronomía, Univ. de la República, URUGUAY
(ITPS Member)

2. Intro: Uruguay Location and Climate
Temperate Climate:
 Annual Rainfall:
1100-1500mm (±200mm,
High variability)
 Mean Temp:
24ºC Summer (± 2ºC),
12ºC Winter (± 1.5ºC)

3. Intro: Area, Population, Agricultural Products
 AREA: 176 215 km² (17.6 Mha) .
 Population:
 People: 3.400.000
 Cattle (Bovine): 12.000.000
 Sheeps: 6.500.000
 Cropped Area: 1.800.000 ha
 Forested Area: 1.000.000 ha
 Other “Traditional”
Export Products:

4. Intro: Uruguay Ecosystem and Soils
 Ecosystem: Grasslands (still 65% of the country)
 Topography: Rolling Plains and Low hills
 Soils: Mollisols and Vertisols (30%) and
Alfisols, Ultisols, Inceptisols, Histosols, Entisols
EEMAC
EELE
UEPAP

5. EELE: Experimental Station INIA-La Estanzuela
 Initiated in 1963
Randomized 3 blocks design,
initiated in 3 consecutive years.
Experimental plots are 25m × 200m,
situated lengthwise on 2–4% slope.
No direct grazing; “cut and return”.
1982:
Cont. Cropping
1982: 3rd. Year Pasture in
Crop-Past. Rot.
“Rotaciones Viejas”
Silty clay loam Typic Arguidoll, 2-4%
slope:

6. Soil Organic carbon content as a function of time in 5 systems studied in a
longterm experiment started in 1963 at INIA La Estanzuela, Uruguay. Sampling
depth: 15 cm (Quinke et al., 2012).
No Till from 2007
Chisel &
disks
Moldboard Plow
-SOC decreased in CC with no N and P fertilization; it last value is 45% of the original.
-In CC with N and P fertilization, SOC equilibrated around 72% of the original.
-SOC content is higher in the CPRs; more with longer time under pasture and less under crops.

7. 0
5
10
15
20
25
CC no Fert. CC Fert. CPR 4C-2P CPR 3C-3Cyrs
SOC content (g/kg). 0-7.5 cm depth, 30 years
using Conventional Tillage
C-MAOM
C-POM
Total C
0
5
10
15
20
25
CC no Fert. CC Fert. CPR 4C-2P CPR 3C-3Cyrs
SOC content (g/kg).,7.5-15 cm depth, 30 years
using Conventional Tillage.
C-MAOM
C-POM
Total C
Rotaciones Viejas, 30 years with
Cnventional Tillage; (Morón, 2003).

8. EEMAC: Expt. Station Mario A. Cassinoni,
Fac. of Agronomy-UDELAR
Soil: Clay Loam Typic Argiudol, less than 1% slope:
Iniciated in 1993.
Continuous Cropping (CC) vs. Crop-Pasture Rotation
(CPR: 3 yrs. crops-3 yrs. pasture), combined with CT
vs. NT in a complete factorial random block design.
In 2000, NT plots were divided to contrast C3
(Soybean or sunflower) or C4 (Sorghum or Corn) in
the summers of the cropping sequences.

9. 0
5
10
15
20
25
30
35
CC-CT CC-NT ROT-CT ROT-NT
SOC (g.kgˉ¹) at 3 depths in 2004, Ernst and Siri-Prieto (2009)
0-6 cm Sig. 5%
6-12 cm NS
12-18 cm NS
a
b
b
b
Lack of differences between CC-NT, ROT-CT, and ROT-NT
explained by low soil erosion (less than 1% ).

10. 0
2
4
6
8
10
12
14
16
18
CCCT ROTCT CCNT-C3 CCNT-C4 ROTNT-C3 ROTNT-C4
SOC (Mg.haˉ¹) in 2003 at 4 depth increments, Salvo et al. (2010).
0-3 cm sig.
3-6 cm NS
6-12 cm NS
12-18 cm NS
(P<0.01)
(P<0.05) (P<0.03)

11. SOC stock (Mg/ha), Total and its physical fractions, 0-3 cm, 10 years in
EEMAC expt.(Salvo et al., 2010).
0
2
4
6
8
10
12
CCCT ROTCT CCNT-C3 CCNT-C4 ROTNT-C3 ROTNT-C4
Total SOC
C-MAOM
C-POM

12. UEPAP: Exp. Unit Palo a Pique, INIA-33
 Initiated in 1995.
 Field Scale (72 ha, 3 ha
plots).
 Direct Grazing with
animals.
 Origin: Undegraded soils
under Natural Grasslands.
 No-Till in all the
experiment.
Silty Loam Abruptic Argiaquolls (in the Summit
and shoulder), 3-5% slope.

13.  Soil Uses for FORAGE (1995):
 1. Continuous Cropping (CC).
 Winter: Annual ryegrass or Oats (direct grazing)
 Summer: Sorghum or Millet (hay or silage)
 2. Crop-Pasture “Short” Rotation (SR).
 2 yrs. Idem CC +
 2 yrs.Pasture. (Red clover & annual ryegrass).
 3. Crop-Pasture “Long” Rotation (LR).
 2 yrs. Idem CC +
 4 yrs. Pasture. (Tall fescue, White clover & Birdsfoot trefoil)
 4. Permanent Pasture (PP)
Original Pasture overseeded with White clover & Birdsfoot trefoil (4 yrs renewal).
 Soil Uses for GRAIN (2005):
 In CC and the 2 yrs. of crops in SR and LR, the
cropping sequence is Sorghum - Black Oat – Soybean - Wheat

14. No-Till Soil Use Intensity impacts on SOC (0-15 cm) in forage (20 yrs)
and grain (10 yrs) crop based rotation systems (Terra and Macedo,
2015).FORAGE BASED GRAIN BASED
PP PPCC CCLR LRSR SR
(Animal Production, kg of live weight/ha:
340 480 480 530)
CC 31% less than PP CC 22% less than PP
aa b
c
c
b b b
CPRotations had 8% less SOC than Permanent Pasture, due to high biomass
extraction in the animal products.

15. SOC stock (Mg/ha), 0-15 cm, 10 years
(Terra and Macedo, 2015)
0
5
10
15
20
25
30
35
40
45
CC Short Rot. Long Rot. PP Nat. Grassland
C-MAOM
C-POM
Total SOC

16. Conclusions
 Crop-Pasture Rotations with No-Till resulted in no SOC content
differences with the experimental original content; but with high
extraction of biomass in animal production an small reduction was
detected.
 Continuos No Till Cropping with predominance of Grass Crops
instead of Soybean or Sunflower resulted in SOC content close
to the original.
 Changes in SOC content due to the different NoTill systems
were detected close to soil surface. SOC changes were mainly
detected in the particulate fraction with low time of residence.

17. Thanks