CHAPTER 5 - ORGANIC FERTILIZERS

Reliable statistics concerning the consumption of organic fertilizers, especially manure, are not available. Brazil has the largest livestock herd in the world (176.4 million head), as well as a large number of pigs (32.6 million), equine (8.4 million), poultry (888.9 million), and sheep (24.2 million), according to IBGE (2003b). All of these animals are potential sources of organic manures. However, the commercial consumption of organic manures is limited to special situations, for example on horticultural and perennial crops, including fruit orchards located close to the producing areas and to intensive livestock producing farms. In the case of grain crops, except in the case of small subsistence or family farming systems or of large farms that integrate crop and animal production in confined systems, the use of organic fertilizers is uncommon.

Even taking into account the low content of N, P₂O₅ and K₂O in most organic fertilizers, the large number of animals, especially cattle, could contribute large amounts of nutrients to Brazilian agriculture. For example, assuming that the 176.4 million head of cattle mentioned above produce an average 24 kg of manure a day (average of 80 percent humidity, 0.55 percent of N, 0.25 percent of P₂O₅ and 0.60 percent of K₂O), it would theoretically be possible to have an annual production of 1 545 million tonnes of manure (176 400 000 x 0,024 x 365), containing 8.5 million tonnes of N, 3.9 million tonnes of P₂O₅, and 9.3 million tonnes of K₂O. This corresponds to 21.7 million tonnes of N+P₂O₅+K₂O, which is more than the total N, P₂O₅ and K₂O contained in the mineral fertilizers used in Brazil in 2002. Vitti and Malavolta (1999) estimated that the manure produced in 1997 in intensive livestock systems involved no more than 5 percent of the 144 million cattle in Brazil, contributing only 371 250 t of N, 155 250 t of P₂O₅ and 405 000 t of K₂O (a total of 931 000 t of N+ P₂O₅+ K₂O), compared with the total consumption of 5 935 500 t of N+ P₂O₅+ K₂O as mineral fertilizers.

Sewage sludge and municipal solid waste treatment plants are much more the exception than the rule in Brazil and the use of their by-products, after transformation into organic compost, is usually restricted to reforestation activities and lawns, with very little use in agriculture. Recent research focusing on the agricultural use of this kind of material (biosolids) has shown its viability for several crops in Brazil (Silva et al., 2000; Melo and Marques, 2000; and Bettiol and Camargo, 2000).

Estimates of the quantity and composition of municipal solid wastes in Brazil are presented in the Table 13. Of the total municipal solid waste produced, 76 percent is deposited in open areas, the so-called lixões (open-air garbage pits), which create substantial social inconvenience caused by effluents, odours and proliferation of insects and animals that are vectors of diseases. The additional social and public health problems due to the large number of people living near the pits are of concern. About 13 percent of the remaining municipal solid waste is deposited in controlled landfills and 10 percent in semi-controlled landfills, whereas 0.1 percent is incinerated and only 0.9 percent transformed into organic compost (AENDA, 2001).

TABLE 13
Composition of municipal solid wastes in Brazil

Source: AENDA, 2001.