ANALYZING THE EFFECT OF DIRECT DRILLING AND CONVENTIONAL TILLAGE WITH
RESIDUE EXTRACTION ON SOIL MACROPOROSITY UNDER DRYLAND FARMING IN A SUBHUMID ENVIRONMENT (NE SPAIN)
Ramón Josa 1, Marta Ginovart* 2, Albert Solé 3
1 Department
of Agri-Food Engineering and Biotechnology, Technical University of Catalonia, Edifici
ESAB-Avda. Canal Olímpic 15, 08860 Castelldefels (Barcelona), Spain, ramon.josa@upc.edu.
2 Department of Applied Mathematics III, Technical University of Catalonia, Edifici ESAB-Avda. Canal
Olímpic 15, 08860 Castelldefels (Barcelona), Spain, marta.ginovart@upc.edu.
3 Estación Experimental de Zonas Áridas, Consejo Superior de Investigaciones Científicas, Gral.
Segura nº 1, 04001 Almería, Spain, albert@eeza.csic.es.
In Mediterranean area available water for crops is restricted by irrigation and/or rainfall regime, and
despite technological advancements and improvements in water distribution and availability for crops;
approximately 77.6% of arable surface in Spain is dryland. Direct drilling (or no-tillage, NT) is a very
widespread practice that is used in several ways: leaving both stubble and straw in place; burning all
crop residues, and removing straw and leaving stubble in place. Conventional tillage (CT) is used to
prepare an adequate seeding bed facilitating the regular, unvarying and early emergency of plants.
However at long-term CT causes intense alteration of the top centimeters of the soil directly affected
by the tillage operations and it has long-term effects on the physical fertility of soils. These effects can
be variable at different soil depths. Infiltration is an essential process for dryland farming in order to
ensure soil water recharge. Micromorphological techniques have been used widely in the assessment
of macroporosity and soil microstructure. Many researchers have contributed actively to provide to soil
micromorphology and to soil micromorphometry its present status of reliable techniques to make
available the necessary links between soil morphology and soil physical properties. They have used
these techniques to assess many geometrical parameters of soil pores for both steady and dynamic
soil studies under a variety of land uses and soil management types.
In research conducted in NE Spain (Josa and Hereter, 2005), cereals and legumes were rotated for
seven cycles using two tillage techniques: CT and NT. During five consecutive years (1995 to 1999)
the straw was removed from plots at the end of each cycle and water content in surface horizons was
monitored during springtime. Throughout all this period the water content in NT was larger than CT.
However, this did not result in an improvement in the yield with NT.
The aim of this paper is to assess the evolution of some soil structural properties after seven years
using these two different tillage systems under dryland farming. These properties are macroporosity
evaluated through micromorphological techniques and bulk density.
The area studied is in NE Spain (Barcelona) and it has a Mediterranean climate. The annual climate
balance shows a water deficit of 187 mm y-1, with a climatic aridity index of 0.76. It is an area of
residual farming amidst woodland and urban areas. It is common practice to remove straw and leave
stubble in place. The experiment and tillage practice of this research were described in detail in Josa
and Hereter (2005). A four-crop grain legume/cereal rotation was implemented using CT and NT. The
tillage practice started in 1994 and soil samples of this work were taken at the end of the experience in
September 2001, after seven complete crop cycles. One plot was tilled by NT and the farming
sequence applied was: mineral fertilization, weed control, drill, weeds control and harvest. Seeding
and harvesting of both plots was carried out with the same machinery at the same time. The other plot
was tilled by means of the CT commonly used in the area, with the following farming sequence:
cultivator, plough, harrow and roller; mineral fertilization, weed control, drill and harvest. Organic
matter management was identical for the two plots: stalks and straw were removed and stubble was
left in place. At the end of seventh consecutive cycle, unaltered soil samples were taken to analyze
the pore space by micromorphological techniques and to measure bulk density. Samples were taken
at the end of the barley crop under dry soil conditions. In each plot, undisturbed samples (blocks) were
taken in two sampling areas: i) middle backslope and ii) lower backslope position. One trench was
opened in each area perpendicular to the tillage-drilling direction. Two layers were identified in
ploughed horizon: upper and lower parts. Undisturbed and oriented samples were taken by means of
Kubiena boxes. In upper layer samples were taken: a) in furrow drilling position (row), and b) interrow
drilling position (interrow). In the lower layer differences between positions were not as obvious as the
previous one and consequently just one set of samples was extracted. Image analysis of vertical
polished sections of resin-impregnated soil samples was. Once polymerized, the blocks were cut into
slices. Polished slices were analyzed separately by both sides. Binary image processing was
performed and the images were analyzed with OPTIMAS 5.2 software in order to measure the twodimensional porosity parameters. Water fluxes in soil are conditioned by the macroporosity
characteristics (total macroporosity, number of macropores and geometrical characteristics of
macropores and continuity of macropores). This is relevant for water infiltration and during the drying
process because each macropore interact with their immediate vicinity to water transmission and to
regulate the air filled porosity. With the idea to characterize the macroporosity effects of both soil
tillage systems CT and NT, three measures were carried out in every slice analyzed: number of
macropores (#); area of macropores (mm 2) and total surface area analyzed (mm 2) and the following
variables were calculated: i) 2-D macroporosity (area of macropores/total surface area analyzed), this
variable presents a good correlation with total porosity measured by other methods; ii) number of
macropores per unit area (NMUA), this variable along with 2-D macroporosity is an indication of fluid
transmission easiness and iii) mean macropore area (MPA), which is used as a simple way to
characterize the effects of tillage system over soil macroporosity, i.e. using the CT/CT:NT/CT. The
bulk density was determined using the excavation procedure. The statistical treatment of the bulk
density data and the parameters of porosity of the polished sections focused on two aspects. First,
they were used to compare the two tillage systems. Second, significant differences between positions:
upper and lower parts of ploughed horizon were sought within each tillage system. Differences
between the row and interrow positions of each treatment were also analyzed, although only for the
samples from the upper layer, according to field observation and assuming that observed differences
in the lower layer were minimum.
Discussion and conclusions from the results obtained and analyzed are summarized as follows.
Significant differences in the pore system were observed in the ploughed horizon after a continuous
application of two tillage systems in a leguminous – cereal rotation cultivated under dryland farming
conditions (NE Spain). Differences were observed between upper and lower layers of the ploughed
horizon using both field and micromorphological techniques. The 2-D macroporosity of the entire
ploughed horizon, lower layer and row positions of the CT treatment, were greater than same 2-D
macroporosity of NT. NMUA values of all CT positions were greater than NT treatment. Bulk density
values of NT are higher than CT in ploughed horizon, upper layer and interrow positions. The upper
layer of ploughed horizon in NT presents more unfavorable physical conditions than CT (lower 2-D
macroporosity, smaller MPA and higher bulk density). The lack of tillage and limited residue
incorporation are likely to be the main causes of the greater 2-D porosity observed in row than the
interrow positions. Differences were detected after harvesting time, when the soil was subjected to
intense drying conditions then, these results must be considered as a residual effect of the tillage
when the upper layer of ploughed horizons were under very dry conditions. In spite of this, top soil
water stress is typical in this area and it recurs annually in most dry lands across the Mediterranean
region. On the other hand, higher NMUA values observed in CT suggests a better aeration of the
ploughed horizon and consequently more favorable conditions for evaporation from the ploughed
horizon of this tillage system. Continuous application of no-tillage simultaneous with extraction of
residues may have caused a decrease of the NMUA in the ploughed horizon, even though stubble
was left in place. Consequently, transmission of water into the profile was reduced and under
Mediterranean climate and over gently sloping surfaces runoff can be increased. The methodology
used has provided a useful insight on the beneficial effects of direct drilling under Mediterranean
dryland conditions.
Keywords: Leguminous-cereal rotation; Row and Interrow macroporosity; Soil micromorphology; Bulk
density; 2-D macroporosity; Mean macropore area.
Reference: Josa R., Hereter A. (2005) Effects of tillage systems in dryland farming on near-surface
water content during the late winter period. Soil and Tillage Research 82, 173-183.