CHAPTER 7 - NUTRIENT BALANCES

The relatively low consumption of nitrogen in relation to phosphorus and potassium was confirmed by a study of Yamada and Lopes (1999), involving calculations of nutrients removed by the 16 main crops in Brazil. This study assumed an average efficiency of 60 percent for nitrogen, 30 percent phosphorus and 70 percent for potassium fertilizers. Using data for the period 1993 to 1996, the authors estimated an average annual deficit of 888 thousand tonnes of nitrogen, even assuming that the whole nitrogen consumption of soybeans and common beans originated from biological N fixation. The estimated deficit for phosphorus was 414 thousand tonnes of P₂O₅ and that of potassium was 413 thousand tonnes of K₂O. Thus, in spite of the substantial increases in the consumption of fertilizers in Brazil in recent decades, Brazilian agriculture is removing from the soil a substantial quantity of nutrients that should be replenished by fertilization, especially with nitrogen. This situation can lead, in the long term, to consequences that are very detrimental to the sustainability of Brazilian agriculture.

To update the results of Yamada and Lopes, 1999 with current data, estimates were made for the year 2000, assuming efficiencies for nitrogen, phosphorus and potassium as before, but considering that only 40 percent of the nitrogen of the common beans originated from the biological N fixation. These estimates represent 94 percent of the cultivated area of the country, involving the 16 main crops.

Overall balances are shown in Tables 15, 16 and 17. A limiting factor in the work of Yamada and Lopes, 1999, as well as in the data for 2002, is that the input of the nutrients was based on mineral fertilizers alone, not taking into account the possible contribution of manure and/or of nitrogen fixation in cover crops in crop rotation systems.

Despite these limitations some aspects regarding the balance of these nutrients are of interest.

The input of nitrogen in the whole country, regions and states, was lower than its removal, giving a negative balance or probably a nitrogen deficiency. The total nitrogen deficit in 2002 was estimated at 859 thousand tonnes compared with the 888 thousand tonnes per year for the period of 1993 to 1996. In terms deficits of nitrogen in kg/ha, some states have deficits higher than the Brazilian average of -16.2 kg of N/ha: Santa Catarina (-44.7), Rio de Janeiro (-41.0), São Paulo (-32.2), Pará (-29.9), Alagoas (-29.2), Acre (-26.2), Roraima (-24.0), Paraná (-22.9), Sergipe (-21.7), Amazonas (-21.1), Federal District (-19.5), Ceará (-16.6) and Paraíba (-16.2).

TABLE 15
Nitrogen balance, 2002

⁽¹⁾ The amounts of effective nutrient applied as mineral fertilizers (assuming 60 percent efficiency).

⁽²⁾ The amounts of nutrient removed with the products of the 16 major crops.

⁽³⁾ The balance (negative or positive) in terms of tonnes and of kg nutrient/ha.

Source: Adapted from IBGE, 2003 and ANDA, 2003.

TABLE 16
Phosphate balance, 2002 (assuming 30 percent efficiency)

⁽¹⁾ The amounts of effective nutrient applied as mineral fertilizers (assuming 60 percent efficiency).

⁽²⁾ The amounts of nutrient removed with the products of the 16 major crops.

⁽³⁾ The balance (negative or positive) in terms of tonnes and of kg nutrient/ha.

Source: Adapted from IBGE, 2003 and ANDA, 2003.

TABLE 17
Potash balance, 2002 (assuming 70 percent efficiency)

⁽¹⁾ The amounts of effective nutrient applied as mineral fertilizers (assuming 60 percent efficiency).

⁽²⁾ The amounts of nutrient removed with the products of the 16 major crops.

⁽³⁾ The balance (negative or positive) in terms of tonnes and of kg nutrient/ha.

Source: Adapted from IBGE, 2003 and ANDA, 2003.

Regarding phosphorus, the total deficit in 2002, was 514 thousand tonnes of P₂O₅ compared with the average of 414 thousand annual tonnes per year for the period from 1993 to 1996. The input of P₂O₅ was larger than the removal by the crops in only two states (Amapá and Roraima). All the Southern states had deficits that where above the Brazilian average (-9.7 kg of P₂O₅/ha): Santa Catarina, -27.0; Paraná, -18.4, Rio Grande do Sul, -14.0. Deficits above the Brazilian average were observed also in the states of Roraima (-13.7), Goiás (-12.4), Mato Grosso do Sul (-11.9), Pará (-10.7), Rio de Janeiro (-10.1) and Acre (-10.0).

For the three macronutrients considered in this balance, the lowest deficit was for potassium. The total deficit for Brazil in 2002 was of 325 thousand tonnes of K₂O, compared with 413 thousand tonnes per year from 1993 to 1996. Five states presented an apparent potassium surplus (Roraima, Amapá, Minas Gerais, Federal District, Espírito Santo and Bahia). An extremely high deficit was observed in the state of Rio de Janeiro (-34.7 kg K₂O/ha). Deficits of between 10.0 and 20.0 kg K₂O/ha were observed in the states of Pará (-19.3), Acre (-17.7), Amazonas (-17.7), Paraná (-16.3), Alagoas (-15.7), Santa Catarina (-15.0), Sergipe (-13.3), São Paulo (-11.2) and Mato Grosso do Sul (-10.3).

Although the balance of nutrients in the Brazilian agriculture needs to be improved for most crops, especially the basic food crops, it is evident that the increased use of mineral fertilizers has played an important role in the development of agricultural productivity and environmental preservation during the past 30 years in Brazil. Figure 11 shows the evolution of the cultivated area and average yields in tonnes per hectare of the 16 main crops (dry weight basis) between 1970/71 and 2002/03. In 1970/71, total crop production was 49.6 million tonnes, fertilizer consumption around 30 kg of N+P₂O₅+K₂O per hectare and the average yield 1.5 t/ha. In 2002/03, production amounted to 184.5 million tonnes, with an average consumption of 138 kg of nutrients per hectare and the average crops yield 3.5 t/ha. During the same period, the cultivated area increased by only 19.4 million hectares (from 36.4 to 56.2 million hectares). These yield increases were obtained through a more appropriate use of mineral fertilizers and other management practices. An additional cropped area equivalent to 71 million hectares of cleared forest would have been necessary if the current total production were to be obtained with the yield average of 1970/71.

* 16 main crops (dry weight basis)
Source: Lopes, Guilherme and Silva, 2003.

An example of the evolution of agricultural production technologies in Brazilian agriculture, especially for the export crops, is shown in Figure 12. This photograph shows the beginning of the harvest of soybeans under the no-till system in the State of Mato Grosso, Centre West region, on soils that until 30 years ago were considered to be marginal for intensive agricultural production. Just behind of the 35 soybean harvesters, 18 planting machines are sowing maize using the no-till system.

The soybean yields obtained by good farmers in the region reach 3.5 t/ha and the yield of maize, the following crop, 6 to 7 t/ha. The production cost of soybeans in the State of Mato Grosso is about US$6.23 per 60 kg bag compared with US$11.72 in the United States of America and the average yield is about 20 percent higher than the American average. In 2002, for the first time in history, the overall average yield of soybeans in Brazil (2.6 t/ha) was higher than the average yield in the United States of America (2.4 t/ha). It is reasonable to state that in the Centre West region, Brazilian farmers are practicing one of the most advanced and sustainable agricultural systems in the world.

Source: Lopes, Guilherme and Silva, 2003.