Case Study: Conservation Tillage
to Save Patzcuaro Lake Watershed
Mario Tiscareño-López
Alma Delia Báez-González
Miguel Velázquez-Valle
Ramón Claverán-Alonso
Centro Nacional de Investigación para Producción Sostenible
Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, SAGAR
Apartado Postal 7-116, Morelia, Mich. 58261, MEXICO
Kenneth N. Potter
The Grassland Soil and Water Research Laboratory
Agricultural Research Service, USDA
808 E. Blackland Road, Temple, TX 76502
Jeffrey J. Stone
Southwestern Watershed Research Center
Agricultural Research Service, USDA
2000 E. Allen Rd., Tucson, AZ., USA
RESUMEN
La cuenca del Lago de Pátzcuaro ha sido expuesta al cultivo del maíz desde
hace más de 3,500 años.
Sin embargo es en los últimos 100 cuando las
actividades humanas sobre los recursos suelo y agua han causado gran daño al
ecosistema.
El cambio en el uso del suelo de una condición forestal a
agricultura anual en las áreas de ladera ha causado que anualmente se pierdan
320 mil toneladas de suelo y azolven el lago a nieveles que provocan
eutroficación y la disminución de la fauna acuática.
Ante este problema el
CENAPROS-INIFAP realizó investigaciones para incursionar en la agricultura
sostenible para protección del ecosistema mediante la aplicación de sistemas de
laboreo de suelo los cuales disminuyeran en forma significativa la erosión y
consecuentemente el azolve del lago. Para tal propósito se han evaluado la
labranza cero y mínima con diferentes niveles de cobertura del suelo a base de
residuos de cosecha.
Esto ha permitido reducir la erosión al 20% en
comparación con el laboreo tradicional que aplican los agricultores. Así mismo
la labranza cero es una alternativa para elevar el nivel friático y recargar el lago
en forma subsuperficial tal como ocurría en su estado sin disturbio. Este estudio
ha dado lugar al Programa Regional de Conservación de Suelos donde
participan más de 1,500 agricultores que habitan en la cuenca.
INTRODUCCION
Agricultural research in Mexico has been largely driven by the concept of
crop productivity, as a means to achieve business profitability and a better
standard of living for farmers. This was greatly inspired by the results of the
Green Revolution at the end of the 1960s, which stated that food production
would be significantly increased in most parts of the world by using hybrid maize
and wheat, fertilizer and pesticide applications and irrigating the prime lands
(Harrington 1996). By many measures, the Green Revolution was a tremendous
success around the world.
In Mexico, maize production grew steadily at an
annual rate of 7.6 per cent until 1967 and the country became self-sufficient in
food crops (Appendini and Liverman 1994). Unfortunately, the impact on crop
yield was less for rainfed crops allocated on marginal lands than for yield
obtained in irrigated areas.
With the possibility of increasing the national food production, during the
1970s and 1980s, state agencies encouraged the expansion of arable land
wherever necessary and possible. Unfortunately available cropland in Mexico is
limited by topography. Only 16 per cent of the land is classified as prime farm
land, mostly allocated in the northern region, suitable for high-input agriculture.
The rest of land is mostly used by 3.1 million small farms (INEGI 1993), either
located on steep-slope terrain or marginal semiarid conditions. However, this
marginal land provides much of the domestic food supply: 14 million metric tons
(SAGAR 1998). The basic staple crops -maize and beans- are grown in the 75
per cent of the rainfed cropland (11.4 million hectares).
The cost of expanding the cropland's frontier has been detrimental for the
nation's natural resources. Mexico's temperate and tropical forests have been
reduced by 30 and 75 per cent since 1960, respectively. According to the World
Resources Institute (1994), Mexico ranks third among countries having the
highest annual rates of diminishing native forests. The impact on the hydrologic
regime by deforestation is perhaps the most distressing point, in light of the fact
that only 12 per cent of the nation's water is on the central plateau, where 60 per
cent of the population and 51 per cent of the cropland are located.
Three
hundred major watersheds, whose total annual water yield approximates 400
billion cubic meters (Albert 1996), undergo a degradation process as a result of
vegetation cover reduction, soil erosion, nutrient losses, agrochemical pollution
and lake eutrophication, among other factors. Concurrent hillslope and gully
erosion from deforestation and inappropriate cultivation of drylands have been
identified on 65 to 85 per cent of the land (Bocco and Garcia-Oliva 1992).
In view of these and other problems, it is urgent to overcome the inability
of current agricultural technology to satisfy the domestic food demands for almost
90 million Mexicans.
This can be accomplished by switching to a new
technological scheme, able to improve agricultural productivity based on the
amelioration of the natural resources for optimal plant growth and animal
production.
This will also gain a significant improvement in the farmers'
environmental and economical living conditions.
This document attempts to
provide an insight on the current research conducted by the National Center for
Sustainable Agriculture (CENAPROS-INIFAP) in Central Mexico directed toward
integration of alternative agroecosystems for sustainable food and fiber
production and the preservation of natural resources.
The research takes place in the Patzcuaro Watershed in Central Mexico, a
basin where maize has been grown for more than 3,500 years by the
Purhepecha ancient culture (Watts and Bradbury 1982). Unfortunately, in this
century, human pressure on soil and water resources has threatened the
regional ecosystems (Toledo et al. 1992).
THE PATZCUARO WATERSHED
One of the most representative sites of the Central-West region of Mexico,
in terms of mankind’s history and natural resource diversity in the North
American Continent, is the Patzcuaro Watershed located in what is known as La
Meseta Tarasca in the State of Michoacan, Mexico.
With rich soils and an
excellent sub-humid temperate climate that characterizes the Mexican NeoVolcanic Central Belt, the Patzcuaro Watershed has not escaped episodes of
deforestation at the hands of local farmers and timber companies under the
support of official programs to increase regional maize productivity and timber
production.
The Patzcuaro Watershed, an area covering 956.2 km 2, is a closed basin
of volcanic formation where runoff from rainfall excess in uplands drains into a
single lake of 89.3 km2. The average annual temperature is 14.5°C and rainfall
averages 1,002 mm per year, mostly distributed from June to October. In most
parts of La Meseta Tarasca, the native vegetation is a mixed conifer and
deciduous forest of Pinus and Quercus genera. Today, the forest is restricted to
46 per cent of the Patzcuaro basin due to anthropogenic causes (i.e., clear
cutting for logging and firewood). The dominant soil type is Andisol, a sandy
loam textured soil derived from volcanic ash with very low bulk density (0.7-0.8 g
cm-3), easily erodible under dry or wet conditions due to its poor structure
(Cabrera 1988).
Annual cropping agriculture is practiced in 25 per cent of the
land, in a topographic array ranging from almost negligible slope near the shore
of the lake to a 45° (100%) slope in some upland sites.
Taking into account the soils and topography of La Meseta Tarasca, the
Patzcuaro watershed is representative of millions of square kilometers of
volcanic lands in the majority of Latin American countries (Zebrowsky 1992),
where the scarcity of prime land obliges small landholders to grow annual crops
under steep-terrain conditions. Andisols, along with other volcanic-derived soils
(Kastanozem, Regosols and Litosols) comprise nearly 60 per cent (1.2 million
km2 ) of the national territory (Aguilera 1969). After decades of applying
conventional agriculture based on mechanical soil movement by local farmers,
these steep-slope lands are becoming less productive because soil erosion and
nutrient losses have been greatly accelerated. As a result, local farmers practice
a cropping system termed "Año y Vez", consisting of planting the fields every
other year as a means to maintain the soil fertility. In the year when the fields
remain uncultivated, cattle are allowed to graze the crop residues and weeds for
direct manure application.
Although farmers have adopted several technological components of the
Green Revolution (application of fertilizers, herbicides and insecticides), the
regional average yield of maize remains very low: 1.5 ton/ha. This is a real
productivity problem considering that maize is cultivated in 44 per cent of the
watershed’s cropland area (21,672 ha) by approximately 10,000 farmers (INEGI
1993). Indeed, such low maize productivity is more a problem of soil fertility
decay than a limitation of the genetic potential of the local maize varieties, which
have proved superior to new varieties and hybrids of maize recently introduced
by commercial breeders. It is also important to mention that the watershed’s high
elevation (2,100 masl) significantly reduces the rate of heat unit accumulation,
which limits the grain yield of synthetic maize germplasm developed for the
lowlands of the Mexican Plateau.
Sedimentation and lake eutrophication constitute the most detrimental off
site effects of the traditional steep-slope agriculture practiced at the Patzcuaro
Watershed, with very adverse consequences on the local fishery and regional
economy. Aquatic weed proliferation and algae blooms have been largely linked
to high nitrogen and phosphorus concentration in storm water runoff from the
upland fertilized fields.
This has directly affected the household economy of
1,200 fishing families since fish population has precipitously dropped as a result
of water quality deterioration along with the excessive fish harvest during the last
years. Annual fish harvest has declined from 900 to 150 kg/ha/yr between 1960
to 1995, indicating the unsustainable patterns of production and consumption
practiced by the watershed inhabitants (Rojas 1992).
ORIENTED AGRICULTURAL RESEARCH
In line with its major institutional objective to achieve sustainable
agriculture in Mexico, CENAPROS guided a multidisciplinary research effort to
identify technological components able to conserve the soil and improve crop
productivity in the Patzcuaro watershed. At the same time, this research site
served as a pilot study for tailoring appropriate soil and water conservation
technology for the nation's watersheds requiring natural resources conservation
plans.
Thus, it was identified that conservation tillage seemed to be an
appropriate technology to solve the above-mentioned problems.
However,
several questions emerged about what system of conservation tillage to apply minimum tillage or no-tillage- and the amount of crop residue (stover) to be left
on the field to minimize soil erosion. It was necessary to keep in mind that crop
residues are the primary animal feed for many farmers.
Therefore, any
recommendation in using the crop residues for soil cover could affect the
adoption of conservation tillage among farmers.
IMPACTS OF CONVENTIONAL AND ALTERNATIVE AGRICULTURE
After four years of investigating different tillage systems to prevent soil
erosion, it was apparent that Andisols are highly susceptible to tillage intensity
(Figure 1). Cropping systems, which use plow- and disk-based tillage
implements, result in highly erodible conditions for the poorly structured soils of
this watershed. Soil losses averaged 3.2 Mg/ha/yr for conventional tillage and 2.6
Mg/ha/yr for minimum-tillage on an 8% slope.
It is evident that a protective
cropping system able to prevent soil degradation must avoid soil disturbance. In
this study, no-tillage was able to lower soil losses to less than 0.3 Mg/ha/yr. This
finding confirmed that conventional agriculture had contributed to lake siltation
during later decades and largely explains why the maximum depth of the lake
has been reduced from 40 to 12 meters between 1940 to 1997 (Chacón, 1993).
3
.
5
1
2
0
3
.
0
1
0
0
2
.
5
8
0
2
.
0
6
0
1
.
5
SoilMsture(m)&Runof(m)
SoilLse(ton/ha)
4
0
1
.
0
2
0
0
.
5
0
.
0
C
o
n
v
e
n
t
i
o
n
a
l
M
i
n
i
m
u
m N
o
t
i
l
l
T
i
l
l
a
g
e
T
r
e
a
t
m
e
n
t
s
0
S
o
i
l
L
o
s
s
e
s
R
u
n
o
f
fS
o
i
l
M
o
i
s
t
u
r
e
Figure 1. Soil losses, runoff and 150-mm layer soil moisture for three tillage
treatments. Soil moisture after harvest (March ).
Minimization of storm water runoff with mulched no-till systems becomes a
key factor to prevent sediment yield and promote infiltration and deep-water
percolation for lake recharge in this closed watershed.
Compared with
conventional tillage, no-tillage reduced runoff by 76% (21.2 mm vs. 88 mm of
runoff) and increased soil water retention to 53% in the first 150-mm soil layer
during the dry season (February to April). This suggests that the watershed
hydrological regime can be significantly modified to improve lake recharge via
groundwater by raising the water table. Chacón (1993) has estimated that since
1940, deep-water percolation has diminished from 12 to 8 per cent due to landuse change. In this study, using the EPIC model developed by Williams (1995),
we estimated that deep-water percolation would be increased from 10 to 20 per
cent by switching from conventional to no-tillage agriculture.
The impact of residue cover on soil losses when using no-tillage was
tested with a range of residue surface cover of 0, 33, 66 and 100 per cent,
consisting of shopped corn stalks from a previous harvest. Figure 2 illustrates
that soil losses are reduced by 80 per cent (0.72 Mg/ha) by leaving 33 per cent of
crop residue with no-till in comparison with zero surface cover in no-till (3.62
Mg/ha). This is important considering that farmers need the crop residues to
feed their animals.
Because of the difficulty in making good residue cover
measurements by the peasants, a practical recommendation is given in terms of
straw rows. For example, “as minimum, leave over the field one of three rows of
straw to get a protective soil cover.”
It is estimated, however, that full soil
coverage with crop residues is reached after six consecutive years of leaving all
crop residues. Water infiltration and soil water content during the dry season
(February - April) have been found to be proportional to residue cover with direct
effects on crop yield (Table 1).
Table 1. Runoff, soil water and crop yield responses by tillage treatment.
No-Tillage / Residue Cover
Tillage
0%
33%
66%
100%
Minimum
Conventional
Runoff (mm)
92.0
24.0
21.2
19.6
92.3
86.9
N in Runoff (kg/ha)*
3.62
2.67
1.94
0.87
9.32
7.05
Soil Moisture (mm)**
48.3
50.4
52.0
57.9
42.0
37.8
7.0
8.0
12.0
12.0
4.0
6.0
Grain Yield (ton/ha)
2.63
3.06
3.18
3.52
3.00
2.84
Straw Yield (ton/ha)
6.14
7.75
6.99
6.84
9.02
8.46
Corn Canopy Cover (%)†
* N-NO3 and N-NH4
** In March (dry season) at the first 150-mm soil layer.
† 30 days after planting (second week of June).
Soil losses (Mg/ha)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1996
0
33
1997
66
1998
100
Residue cover (%)
Figure 2. Reduction of sediment yield in no-tillage treatments by the effect of
residue cover.
Rainfall simulator experiments were conducted on 3 m 2 plots to quantify
the effects of residue on infiltration rates. It was found that the soil saturated
hydraulic conductivity increased from 24 mm/hr for conventional tillage with zero
mulching to 93 mm/hr for no-tillage and 100 per cent residue cover. Residue
cover also reduced soil water evaporation by avoiding direct solar radiation and
wind effects over the soil surface. For no-tillage, almost 10 mm of additional
water are stored in the first 150-mm soil layer when applying 100 per cent
residue cover in comparison to zero mulching. This extra water allows a better
establishment of rainfed corn, as corn canopy cover expressed 30-days after
sowing (Table 1).
In addition, crop yield responses have improved when applying no-tillage
and crop residues as mulch. No-tillage with 100 per cent residue cover improved
grain yield by 0.7 Mg/ha with respect to maize under conventional tillage. This is
largely attributed to reductions in runoff and nitrogen losses and improvement of
soil water retention. Recalling that the regional average maize yield is 1.5 Mg/ha,
this increment of crop yield is perhaps the most attractive technological response
in adopting conservation tillage.
Another branch of this research has been a modeling effort to extrapolate
point-based experimental data to other watershed sites requiring information on
soil erosion rates. Plant growth and soil erosion modeling have been applied to
estimate the long-term impacts of no-tillage technology in order to preserve soil
and water resources and to design soil conservation plans by prioritizing the
most degraded cropland areas of the watershed.
Soil erosion and crop growth models have been applied; such as the
Erosion-Productivity Impact Calculator (EPIC), the Soil and Water Assessment
Tool (SWAT), the Groundwater Loading and Evaluation of Agricultural
Management Systems (GLEAMS), the Infiltration-Runoff Simulator (IRS), the
Water Erosion Prediction Project (WEPP) and the Decision Support System
(DSS) models. Model parameterization in this study involved rainfall simulation
studies to determine hydraulic and erosion parameters required by processbased models to simulate crop-soil management scenarios that comprise
technological components of alternative agriculture.
Process-based modeling was interfaced with satellite imagery to assess
actual land-use and Geographic Information Systems to graphically represent the
spatial variability of crop productivity and soil losses in cropland areas subjected
to conventional tillage as well to assess the potential of no-tillage agriculture for
watershed restoration.
Figure 3 presents estimates of soil loss spatial variability in the Patzcuaro
Watershed under current conventional agriculture and no-tillage agriculture. Soil
losses range from less than 0.1 ton/ha/yr on fields with negligible slope to 250
ton/ha/yr on 45 slope conventional-tilled fields. At the watershed scale, soil
losses under conventional tillage averaged 16.3 ton/ha/yr.
It was predicted,
however, that no-tillage agriculture would reduce soil losses to 0.74 ton/ha/yr in
this watershed; within a range of 0.12 to 14 ton/ha/yr. This means that even with
the use of no-tillage cropping systems, some high-slope areas would be exposed
to high erosion rates, and for them, reforestation is the most appropriate
alternative to protect the ecosystem.
Therefore, an important aspect of this
research is to identify cropland areas requiring soil conservation practices other
than implementing no-tillage agriculture.
Conventional Tillage
No-Tillage
Lake
e
Forest
Ton / ha / year
< 0.2 1
10
20
30
50
70
130
180
250
300
Fig. 3. Soil losses in cropland areas with maize cultivated under conventional
and no-tillage.
330
FINAL COMMENTS AND CONCLUSIONS
In Mexico, as in some areas of the world (Sain and Barreto 1996), the
adoption of conservation technology can fail because of technical factors:
insufficient crop residue because of low system productivity or economic reasons
due to high value of residue used as forage (Erenstein 1996). In most parts of
the country, there is a great limitation of conservation tillage machinery (e.g.,
residue shredders and no-tillage planters) and farmers very frequently desist of
applying this type of agriculture. Even more, the burning sorghum and wheat
residue is a common practice for soil preparation because of the difficulties in
planting
the
following
crop
using
conventional
seeder.
Thus
any
recommendation to leave crop residues on the field requires appropriate
shredders or residue cutters.
However, any technical aspect that limits the
adoption conservation tillage does not seem too difficult to subdue as compared
with the farmers' deeper agricultural tradition in applying conventional tillage.
Agricultural research at the Patzcuaro watershed had allowed the
identification of soil conservation practices able to reduce soil erosion to
minimum levels and extend the life span of the Patzcuaro watershed. Also, this
research has provided a protocol for basic information acquisition to identify
watershed areas requiring soil conservation plans in Mexico.
Modeling
hydrologic and soil erosion processes is a crucial planning tool in developing
countries such as Mexico, but high-quality long-term databases are required, that
very often do not exist, indicating there is still much to do.
Although no-tillage systems that improve corn yield seems to be the
solution for adopting conservation tillage among farmers; research is needed to
identify technological components required to integrate agroecosystems.
Several technological components need to be tested, like nitrogen fixation using
legumes to reduce dependence on inorganic fertilizers, development of
appropriate agricultural machinery for small landholding farmers that use animal
traction and hand-driven instruments, and integrate pest management practices
to reduce the usage of environment-degrading pesticides, among others. Not
only in Mexico, but also for most countries of Latin America, agriculture needs a
major change to increase and sustain food production at adequate levels
according to demands of current and future human population. Land degradation
had been occurring because of frequent application of inappropriate technology
in areas where soil quality or topography imposes severe difficulties.
New
conservation tillage machinery is now available in developing countries as
imported prototypes from developed countries.
However; the cost, size and
conditions for which they were developed often limit their acquisition and proper
technology application by farmers.
However, it is important to mention that farmers are not willing to reforest
their croplands given the low and sporadic income obtained from logging the
forest. With conservation tillage, farmers can grow annual crops, which include a
dietary staple -maize-, which guarantees part of their family food needs. Finally,
it is possible to conclude that restoration of the Patzcuaro Watershed is feasible,
it can be done by implementing no-tillage technology to avoid soil mechanical
movement along with application of crop residue as mulch. This technology
allows an 80 per cent reduction in soil erosion and increases crop productivity 24
per cent at the same time, as compared with conventional tillage.
REFERENCES CITED
Aguilera, H.N., 1969. Geographic distribution and characteristics of volcanic ash
in Mexico. Panel sobre suelos derivados de cenizas volcánicas de América
Latina. Centro de enseñanza e Investigación, Instituto Interamericano de
Ciencias Agrícolas de OEA., Turrialba, Costa Rica, FAO-OEA.
Albert, L.1996. Sobreexplotadas las fuentes hídricas del país. In: La Jornada
Ecológica. 4(37):3-7.
Appendini, K. and D. Liverman 1994. Agricultural policy, climate change and food
security in Mexico. Food Policy 19(2):149-164.
Boco, G. and F. Garcia-Oliva 1992. Research gully erosion in Mexico. J. Soil and
Water Cons. 47(5):365-367.
Cabrera, C.F.1988. Algunos Criterios para Evaluar los Sistemas de Labranza
Aplicados
a
Dos
Suelos
de
México.
M.Sc.
Thesis,
Colegio
de
Postgraduados, Mexico. 140 pp.
Chacón, A.R.1993. El Ecosistema Lacustre In: Plan Pátzcuaro 2000:
Investigación Multidisciplinaria para el Desarrollo Sostenido. V. M. Toledo, P.
Alvarez I. y P. Avila (eds.). Fundation Fiedrich Ebert. México, D.F. pp 91-133.
Erenstein, O. 1996. Evaluating the Potential of Conservation Tillage in MaizeBased Farming Systems in the Mexican Tropics. Natural Resources Group,
CIMMYT, Mexico14 pp.
Harrington, L. 1996. Diversity by Design: Conserving Biological Diversity Through
More Productive & Sustainable Agroecosystems. CIMMYT's Natural
Resource Group.
Doc. presented at Biodiversity and Sustainable
Agriculture, a workshop by the Sweden Scientific Council, Ekenas, Sweden,
Aug. 14-17, 1996.
INEGI. 1993. Censo Agropecuario 1991. Instituto Nacional de Estadística,
Geografía e Informática. Compact Disc. Mexico.
Rojas, P. 1992. Producción Pesquera. In: Plan Pátzcuaro 2000: Investigación
Multidisciplinaria para el Desarrollo Sostenido. V. M. Toledo, P. Alvarez I. y
P. Avila (eds.). Fundation Fiedrich Ebert. México, D.F. pp135-158.
SAGAR 1998.
Pronóstico Climático 1998. Documento de la Conferencia de
Prensa del Sr. Secretario Ing. Romárico Arroyo Marroquín. Secretaría de
Agricultura, Ganadería y Desarrollo Rural. México.
Sain, G.E. and H.J. Barreto. 1996. The adoption of soil conservation technology
in El Salvador: Linking productivity and conservation.
J. Soil and Water
Cons. 51(4):313-321.
Toledo, V.M., P.Alvarez-Icaza and Patricia Avila (Eds). 1992. Plan Patzcuaro
2000: Investigación Multidisciplinaria para el Desarrollo Sostenido. Fundation
Fiedrich Ebert Stiftung. 320 pp.
Watts, R.C. and J.P. Bradbury. 1982. Paleoecological studies at lake Patzcuaro
on the west central Mexican plateau and at Chalco in the basin of Mexico.
Quaternary Research Review, 17:56-70.
Williams, J.R. 1995. The EPIC Model, In: V.P. Singh (Ed) Computer Models of
Watershed
Hydrology,
pp.
909-1000,
Chap.
25
Water
Resources
Publications, 1144 pp.
World Resources Institute. 1994. A Guide to The Global Environment: People
and the Environment. Oxford University Press. New York, USA.
Zebrowsky, C. 1992. Indurate volcanic soils in Latin America. Proceed. of First
International Workshop of Indurate volcanic soils, held at Mexico City,
October 20-26, 1991. Terra, vol. 10:15-23.