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124 Nitrogen in the Environment
P
ART B. NITROGEN MANAGEMENT IN SOUTHERN BRAZIL AND WESTERN PARAGUAY
T.J.C. Amado and F.L.F. Eltz
Soils Department, Federal University of Santa Maria, Santa Maria, Rio Grande, do Sul, Brazil
1. AGRO ECOLOGICAL CHARACTERISTICS OF SOUTHERN BRAZIL
WESTERN PARAGUAY
The oriental region of Paraguay and the plateau of Southern Brazil are two
important croplands in the Southern Cone ( Figure 1 ). Paraguay has more than 40
million hectares, which 16 million are located in oriental region. About 61% of the
total area is used for beef cattle raising. The oriental region is the most developed
with around 98% of total population of the country. The Paraguay ’ s cropland area
is around 2.3 million hectares. The agriculture contributes for 16% of total income,
while beef cattle raising contributes for 7.9%. The plateau of Southern Brazil is
spread by Rio Grande do Sul, Santa Catarina, and Parana States. Until the 1960s,
it was covered by forest of Araucaria ( Araucaria brasiliensis A. Richard). The area
was almost completely deforested, and nowadays it is the most important agriculture
Southern
region
BRAZIL
Paraguay
Western region
Figure 1 . Major agriculture zones in Paraguay and Southern Brazil. The areas in
the square will be focussed on this chapter.
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Nitrogen Management in Field Crops of the Southern Cone of Latin America 125
area in Southern Brazil, with around 8 million hectares for grain production. In both
regions of Paraguay and Brazil, soybean ( Glycine max (L.) Merril) is the crop with
higher economic relevance, followed by maize ( Zea mays L.), irrigated rice ( Oryza
sativa L.), sorghum ( Sorghum bicolor (L.) Moench), wheat ( Triticum aestivum L.),
black beans ( Phaseolus vulgaris L.), and sunflower ( Helianthus annus L.), among
others.
In the agriculture calendar year of Paraguay and Southern Brazil, it is possible
to have at least double cropping systems, the first crop in winter and the second
one in the summer season. The winter crops are usually planted from April to June
and summer crops are planted from September to December. Some variation in this
agriculture calendar has been used as two summer crops like short cycle corn fol-
lowing by soybean, or black beans following corn. The second summer crops usu-
ally has lower yield potential because the unfavorable climatic conditions. In this
intensive cropping system sometimes it is not possible to grow a winter crop or a
cover crop.
These regions show remarkable differences in agricultural production systems
depending on climate, landscape, soil type, and mainly socioeconomic condi-
tions. Paraguay and Southern Brazil had numerous smallholder farmers with lim-
ited access to capital and technologies, which results in medium to low crop yields.
These farms usually have less than 50 ha, family-operated, steep slopes, and semi-
subsistence smallholdings ( Bollinger et al., 2006 ). The agricultural production usu-
ally is commercialized in regional market. On the other hand, these regions also
had commercial farms with high use of technologies, with medium to high crop
yields. These farms are capital intensive, with more than 100 ha, gentle undulating
landscapes, and commercially orientated agricultural enterprises ( Bollinger et al.,
2006 ). In this case, the agricultural production goes to national and overseas mar-
ket. Therefore, the average data of cropland yields, inputs, and so on … for these
regions should be carefully analyzed, because it is an average of contrasting agri-
cultural systems. Sometimes this average does not reflect neither the smallholder
farm nor the commercial farm.
The deforestation process in Southern Brazil happened earlier than in Paraguay.
The expansion of the cropland area was associated with poor soil management
practices like burn, fallow, monocropping, and intensive tillage that resulted in
severe water erosion process. The soil degradation process could be expressed by
soil organic matter (SOM) decline that achieved 50–75% of original content in only
two decades. Cassol (1984) estimated that during the 1980s, two-thirds of agricul-
tural land in Southern Brazil showed some level of degradation, often manifested in
poor rainfall infiltration, structural degradation, and compaction. Although farmers
at that time used terraces and contour crop, in an attempt to reduce runoff and soil
erosion, these were rarely efficient. The agriculture system with conventional tillage
(plow two disks) resulted in bare soil, in a rainfall erosivity that ranged from 5,000
to 12,000 MJ mm/ha/h/year, which was unsustainable. In the early 1970s, no-tillage
(NT) was introduced as the main alternative to erosion control. The system had a
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126 Nitrogen in the Environment
fast growth since the 1990s, achieving nowadays around 80% of cropland in these
regions ( Amado et al., 2006 ). This conservation system restores at least partially
the original soil productivity loss and allows a new cycle of agriculture develop-
ment to the region described by Bollinger et al. (2006) as “ Brazilian Zero Till
Revolution. ”
2. CLIMATE AND SOIL
A brief description of the climate and the major soil types is presented to con-
tribute to a better understanding of common management practices. The weather of
these regions is predominant tropical and subtropical, with hot and wet summer and
cold winter. In Paraguay the average annual temperature is 18°C. The precipitation
is high in summer (October–March) and low in winter (July–August). The annual
average precipitation is 1,700 mm. Figure 2 shows the climatic data from San Juan
Bautista, Missiones Department, located at coordinates 26° 4 0 S and 57° 0 9 W
with 126 m of elevation. Missiones is an important agriculture and beef cattle rais-
ing region in Paraguay.
In Southern Brazil, the predominant weather is subtropical type Cfa, following
Köeppen classification. Figure 3 shows the climatic data from Passo Fundo (Rio
Grande do Sul State), located at coordinates 28° 2 5 S and 52° 4 0 W with 684 m o f
elevation. Passo Fundo is an important agriculture region in Southern Brazil. The
average annual temperature is 17.5°C and total annual precipitation is 1,785 m m .
The total real evapotranspiration is 823 mm. The monthly rainfall distribution is
more regular than in Paraguay, with a small difference between summer and winter
seasons. The average temperature of the hottest month is around 24°C (January) and
the average of the coldest month is around 13°C (July). A positive balance period
in terms of water accumulation occurs during all the months of the year, without a
negative period. Despite of this very positive annual climatic water balances, short
droughts are common. The variability of the rainfall regime causes frequent local
short droughts. The climatic variability in Southern Brazil is associated to meet of
cold air mass from Argentina and hot air mass from Central Brazil and Paraguay.
Droughts are more common from December to February and from May to July,
increasing the risk of yield reduction in drought sensitive crops like corn. In sum-
mer, heavy rainfall is common, with high erosivity index, causing severe water ero-
sion. The plateau of Southern Brazil has an undulating landscape, different from the
flat Pampas of Argentina, increasing the erosion risk.
The expansion of cropland in Southern Brazil was associated to intensive lime
application and phosphorus (P) fertilization. These soils, under original conditions,
are acid with aluminum and iron toxicity and very low P levels. The Kaollinite clay,
with low activity, is predominant in these soils. The high aluminum and iron sesqui-
oxides contents cause decrease in P availability, due to high P sorption, especially
when tilled. As a consequence, P is the most common deficient nutrient in Brazilian
tropical and subtropical soils. Therefore, to produce competitive yields, these soils
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Nitrogen Management in Field Crops of the Southern Cone of Latin America 127
35
30
25
Temperature (°C)
20
15
Average of minimum
Average of maximum
San Juan Bautista
10
Jan Feb Mar Apr May Jun
Months of year
Jul Aug Sept Oct Nov Dec
(a)
Figure 2 . Temperature (a) and precipitation (b) data from San Juan Bautista,
Paraguay. (Adapted from www.allmetsat.com )
Precipitation (mm)
San Juan Bautista
Jan Feb Mar Apr May Jun
Months of year
Jul Aug Sept Oct Nov Dec
200
180
160
140
120
100
80
60
40
20
0
(b)
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128 Nitrogen in the Environment
250
(a)
200
150
mm
100
50
0
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec
Precipitation
Potential evapotranspiration
Figure 3 . Climatic data from Passo Fundo (a) and 30 years average of global solar
radiation of state Rio Grande do Sul, Brazil (b).
550
(b)
500
450
400
350
Cal/cm
2
/dia
300
250
200
150
7 8 9 10 11 12
Months
Rio Grande do Sul – 30 years
123456
need fertilizer and lime input. On the other hand, these soils have good physical
properties like structure, depth, aggregation, and porosity. In such soils, SOM main-
tenance or buildup is crucial to ensure good crop productivity, once 70–95% of cat-
ion exchange capacity is found in SOM ( Bayer and Mielniczuk, 1999 ). Therefore,
it is often postulated as the most important single indicator of the soil restoration
process in Southern Brazil ( Conceição et al., 2005 ).
In Table 1 , some representative chemical soil analysis from Paraguay and South
Brazil are presented. In both agriculture regions of Paraguay and Southern Brazil,
the potassium (K) level is medium to high, while the pH and P are low. Some levels
of nutrients also are a result of fertilization history.
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Table 1.
Soil characteristics of main cropland counties in Paraguay and Brazil (0–20 cm soil depth).
State/County Country Localization Soil
pH
water
Clay
(g/kg
)
SOM
(%)
P
1
(mg/dm
3
)
K
(mg/dm
3
)
Missiones (San
Patricio)
Paraguay
26° 59 S
56° 44 W
Ultisol
5.1
250
2.7
4.3
126
Itapúa (Bela Vista) Paraguay 27° 08 S
56° 03 W
Ultisol 6.2 355 2.5 3.5 195
Alto Parana (Iguazu) Paraguay 25° 27 S
55° 02 W
Oxisol 5.3 395 2.9 7.6 203
Rio Grande do Sul
(Cruz Alta)
Brazil 28° 36 S
53° 30 W
Oxisol 4.5 435 3.2 19.0 82
Santa Catarina
(Campos Novos)
Brazil 27° 24 S
51° 13 W
Oxisol 5.6 760 3.5 3.0 100
Rio Grande do Sul
(Palmeira das
Missões)
Brazil 27° 53 S
51° 18 W
Oxisol 4.5 630 3.1 7.2 167
1
P determined by Melich-1.
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130 Nitrogen in the Environment
3. EVOLUTION OF FERTILIZER CONSUMPTION AND GRAIN
YIELDS ACHIEVED
Soybean, corn, and wheat are extensively cropped in Southern Brazil agri-
cultural lands, showing a steady improvement in their yields ( Figure 4 ). Since the
last two decades there was not a relevant change in land area under agricultural
use in Southern Brazil, the total grain production of this region has increased con-
sistently ( Schlindwein and Gianello, 2006 ). As an example, in Paraguay, average
soybean yield in 1980s was 1,670 kg/ha and in the 1990s it increased to 2,639 kg/ha
( FAOSTAT, 2005 ). The introduction of high-yielding technologies, including
selected genotypes, modern pesticides, and integrated management practices for
disease and pest control, soil conservation practices, and fertilizers use, partially
explains the positive change in crop productivity in this region ( Diaz-Zorita et al.,
2006 ). The improvement in soil quality due to long-term adoption of NT also
should be stressed as one of the major causes of this yield improvement. Many
farms have been using continuous NT for more than 20 years and the soil quality
has improved markedly.
4,000
3,000
2,000
Grain yield (kg/ha)
1,000
0
1965 1970 1975 1980 1985
Year
1990 1995 2000 2005
Soybean Wheat Corn
Figure 4 . Increase in yields of main grain crops in Rio Grande do Sul state,
Southern Brazil. (Adapted from Schlindwein and Gianello, 2006) .
In the particular case of fertilizers, average use of nutrients for agricultural pro-
duction increased in the region since the 1970s to the present ( Table 2 ), showing
differences in the proportion of the applied nutrients in relation to other Southern
Cone countries ( Table 3 ). In Southern Brazil and Paraguay, N, P, and K are almost
evenly used, while in the rest of the region a relative low amount of K fertilizers is
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Nitrogen Management in Field Crops of the Southern Cone of Latin America 131
Table 2.
Evolution of the use of fertilizers in Brazil and Paraguay.
Countries
Period Brazil (Mt/year) Paraguay (Mt/year)
Total of Southern
Cone (Mt/year)
1970–1979 2,359 4 2,657
1980–1989 3,340 11 3,772
1990–1999 4,814 38 5,904
2000–2004 7,290 118 8,796
Source : Adapted from Diaz-Zorita et al. (2006) .
Table 3.
Relative use of N, P, and K fertilizer in Brazil, Paraguay and average of Southern
Cone Countries.
Countries
Nutrient Brazil (%) Paraguay (%)
Average of Southern
Cone (%)
Nitrogen 24 28 40
Phosphorus 36 40 42
Potassium 40 32 18
Source : Adapted from Diaz-Zorita et al. (2006) .
applied ( Diaz-Zorita et al., 2006 ). Also, the Brazilian fertilizer market differs from
the ones in the rest of the Southern Cone, because of the high proportion of P and
K use in relation to N ( Table 3 ). The low use of N (59% of the average N use in
South America countries, Table 3 ) in grain production could explain partially the
low corn yield (72% of the average yield in South America) and wheat yield (89%
of the average in South America) during the period 2000–2004 ( Diaz-Zorita et al.,
2006 ). Figure 5 shows that the consumption of fertilizer in corn, rice, and wheat
has not been growing in the last 5 years, limiting the increase of yield ( Figure 4 ).
The increase in fertilizer use in soybean ( Figure 5 ) is related to the improvement
in yield (110% of the average of the other countries in South America, during the
period 2000–2004). Crop rotations, including soybean/maize (summer rotation)
and soybean/wheat (winter rotation), partially alleviate the problem of unbalanced
crop use of fertilizer, due to residual soybean fertilizer use by marginal crops. Many
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