Crop roots and crop residues management: impacts on soil structure under
zero tillage
Fuentes M1, Solís Paola1, De León F1, Castorena C2, Govaerts B3
1
Universidad Autónoma Metropolitana-Xochimilco, Laboratorio de Fisiología y Tecnología
de Cultivos, Calzada del Hueso 1100, Col. Villa Quietud, 04960, D.F., México.
[email protected]
2
Colegio de Postgraduados, Laboratorio de Fertilidad, IRENAT Km 36.5 Carretera MéxicoTexcoco, Montecillo, CP 56230, Mexico.
3
International Maize and Wheat Improvement Centre (CIMMYT), Apdo. Postal 6-641, 06600
D.F., Mexico.
Keywords: conservation agriculture, porosity, roots-soil interplay, thin sections
Introduction
The soil physical condition plays a key role in processes such as aeration, water infiltration,
water capillary movement, accessibility of soil solution to particle surfaces for chemical
exchange, sorption reactions and biological activity. Root-soil interplay and crop residues
management influence soil aggregation and increased soil pore complexity (Gregory et al.
2006). Total soil porosity and pore sizes are important parameters to assess soil
structure. However the pore type identification provides more information regarding the
movement of water and air in the soil, than the pore sizes. In a long-term experiment in the
International Centre for Maize and Wheat Improvement (CIMMYT) in the central highlands
of Mexico we investigated the effect of different management practices, i.e. zero tillage (ZT),
conventional tillage (CT) with (+r) or without (-r) residues retention and maize-wheat
rotation (R) or monoculture (M), on physical and chemical soil quality. After 15 years of
continuous practice, ZTM+r and ZTR+r resulted in increased soil physical quality compared
to the other practices (Govaerts et al. 2006; Fuentes et al., 2009), while removal of crop
residue resulted in reduced soil quality, except for ZTM-r with wheat that showed
intermediate soil physical quality (especially aggregation). It seemed that the continuous
cultivation of wheat could compensate somehow for the removal of the residue as this
treatment did not show the same degree of degradation as the other ZT plots with residue
removal. We hypothesized that the interplay between soil-roots under wheat leads to a more
conducive pore soil system compared to maize systems. The current research evaluated the
influence of two root systems (maize and wheat) and crop residues management on the soil
pore system.
Materials and Methods
The study was conducted at El Batán (Experimental Station of CIMMYT), situated in the
semi-arid, subtropical highlands of Central Mexico, in a Haplic Phaeozem having 250, 370
and 380g 1000 g-1 of sand, silt and clay content, respectively. The experiment was set up in
1991 and consisted of thirty-two treatments of which the current research only considered six
treatments: ZTM-r, ZTM+r and ZTR+r under maize or wheat. The total porosity, compound
packing voids, channels or bio-pores and fissures were quantified on thin sections which were
obtained from root-centered positions at four soil depths (0–5, 5-10, 10-15 and 15-20 cm) of
undisturbed soil samples. Complete or selected areas of thin sections were photographed and
the images processed with the program Image-Pro®; statistical analysis consisted of a linear
model and an analysis of variance were done in order to test the experimental factor effects
on the studied variables with SAS® software.
Results and Discussion
Treatments affected total porosity in the 0-5 cm (P<0.01) and in the soil layers of 5-10, 10-15
and 15-20 cm (P<0.05). In the 0-15 cm layer the greatest total soil porosity was found in the
soil under conservation agriculture (CA or ZTR+r) cultivated with maize (Figures 1 and 2).
CA cultivated with wheat showed a lower total porosity than CA cultivated with maize. We
assume that the wheat roots-soil relationship created better soil conditions for the
development of maize roots, while the interplay maize roots-soil reduced soil porosity and
soil physical quality for wheat growth. Gregory et al. (2006) showed that wheat roots
promoted aggregate formation to a larger extent than maize roots. In the 0-10 cm soil layer,
the soil under ZTM+r (wheat) exhibited high porosity (second place of all treatments),
confirming the hypothesis that the wheat root system improves the soil physical condition
(Figure 1). The soil with rotation showed a lower proportion of fissures than soil with
monoculture (wheat and maize) (Table 1 and Figure 2). This parameter is an indicator of soil
degradation and the rotation practice wheat-maize improves the soil physical quality
compared to monoculture practice.
The soil under ZTM+r (wheat) had more bio-pores (formed mainly by roots) than ZTM+r
(maize), the same pattern was observed when ZTM-r (wheat) was compared to ZTM-r
(maize) (Table 1). The samples from ZTM+r showed more pores in the 0-5 cm layer than the
samples from ZTM-r. The crop residues are involved in the formation of soil aggregates,
which in turn is associated with pore formation. In the ZT treatment the crop residues are
accumulated in the 0-10 cm soil layer (Fuentes et al, 2009), thus the differences in porosity
between soils with and without residues were more evident in the first centimeters of the soil
profile. The greatest proportion of compound packing pores in 0-20 cm was found in soils
under CA cultivated with wheat or maize compared to the other treatments (Table 1). This
type of pores favors water movement in the soil, because they are interconnected and they are
located between soil aggregates (Fox et al., 2004). In the 0-10 cm layer the proportion of
compound packing pores was greater in soils under ZTM-r (wheat) than in soils under maize.
We conclude that the root wheat-soil relation favors the formation of pores, especially biopores and composite packaging pores. These kinds of pores contribute to the soil physical
quality, however research must take into account that roots per se do not generate a fully
satisfactory soil structure; it is necessary to keep crop residues at the soil surface.
Conservation agriculture improves soil porosity (see Figure 2), though it is necessary to use
adequate crop rotations in order to promote effective root-soil relations.
Total soil porosity (%)
70
60
50
0 to5 cm
5 to 10 cm
10 to 15 cm
15 to 20 cm
LSD 7.6
LSD 6.2
LSD 5.4
LSD 5.7
40
30
20
10
0
ZTMm-r ZTMw-r ZTMm+r ZTMw+r ZTRm+r ZTRw+r
Figure 1 Total soil porosity maize (m) and/or wheat (w), zero tillage (ZT), rotation (R) and
monoculture (M), with residues (+r) or without residues (-r) treatments at CIMMYT's longterm tillage sustainability trial El Batán (México). Data from thin sections image analysis.
ZTR+r
ZTMm+r
ZTMt+r
ZTMm-r
A
A
A
A
B
B
B
B
C
C
C
C
D
D
D
D
Figure 2 Thin sections (original size 5 by 7 cm) image, different soil profile A: 0-5cm, B: 510 cm, C: 10-15 cm and D: 15-20 cm under maize (m) and/or wheat (w), zero tillage (ZT),
rotation (R) and monoculture (M), with residues (+r) or without residues (-r) treatments at
CIMMYT's long-term tillage sustainability trial El Batán (México).
Table 1. Compound packing voids and channels maize (m) and/or wheat (w), zero tillage (ZT), rotation (R)
and monoculture (M), with residues (+r) or without residues (-r) treatments at CIMMYT's long-term tillage
sustainability trial El Batán (México). Data from thin sections image analysis.
Treatments
Depth (cm)
ZTMm-r
ZTMt-r
ZTMm+r
ZTMt+r
ZTRm+r
ZTRt+r
LSD
Channels or Biopores
(cm 100 cm-2)
0-5
5-10
10-15
0.37
0.81
0.80
2.94
0
0.15
2.1
2.08
2.94
6.18
7.35
1.55
0.62
4.7
0.83
0.95
3.73
7.07
1.28
3.98
3.6
15-20
Compound packing voids
( cm 100 cm-2)
0-5
5-10
10-15
15-20
2.01
2.29
1.89
6.70
2.88
3.74
3.8
3.63
29.00
32.63
38.86
62.81
32.20
12.3
0
0
0
1.83
3.62
7.25
6.7
3.54
4.10
5.80
5.59
30.25
27.30
7.4
1.97
0
3.91
2.86
16.03
2.09
8.2
Fissures
(cm 100 cm-2)
0-5
5-10
1.74
3.01
2.68
1.53
0
1.11
1.0
1.97
4.64
9.76
6.21
1.19
0.85
4.9
10-15
15-20
8.8
7.96
9.36
3.4
2.25
3.47
3.9
18.13
6.91
6.75
6.55
2.57
3.7
4.1
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