A lot of food has already been harvested from the soil of São Paulo. But over the years, and in particular with the planting of a single crop, the cultivable lands have been losing their productive capacity. One of the ways out for this problem may lie with the recently concluded work by a researcher from the Campinas Agronomic Institute (IAC), Hipólito Assunção Antônio Mascarenhas and his collaborators. The study assessed the performance of the crops of corn, rice and soya, planted in areas formerly occupied with Crotalaria juncea, a plant used as green fertilizer and in the manufacture of cigarette paper, twine and rugs. The results confirmed the researchers suspicions: the annual crops of corn and rice become more productive when sown after crotalaria or soya, two representatives of the Fabaceae family or, as they are better known, legumes.
In the case of rice, the tests revealed that cultivating them continuously in a single area interferes directly with their performance. “On the average of the three years, rice production increased by 88% after two legumes (crotalaria and soya), when compared with the cereal planted without rotation”, says Mascarenhas. With regard to soya, the study showed that rotation and a succession of crops does not exert nay influence on its development and productivity. These practices are recommended, though, to control attack by nematodes (a kind of worm), a pest of great economic importance for this crop. Another finding was that the use of varieties of soya, corn and rice that tolerate the acidity of the soil is fundamental to their growth, particularly in areas of low fertility.
Legumes have a peculiar characteristic that transforms them into great allies of the farmer. In the presence of certain bacteria of the Bradyrhizobium genus, they are capable of absorbing nitrogen from the atmosphere, enriching the soil with one of the most important nutrients for plant species to develop. Depending on the quantities of this element fixed, one may even dispense with nitrogenous chemical fertilizing with ammonium sulfate or urea both for soya and for crops that may come after it.
The use of Crotalaria juncea as green manure is a very widespread practice in the sugarcane crops of the state of São Paulo, particularly on degraded soil that needs to be recovered. Besides supplying the soil with nitrogen, it is a plant that offers advantages, such as the supply of a green mass to cover the earth during the vegetative cycle and, and at its end, with dry matter that when incorporated into the soil combats erosion and prevents the proliferation of weeds.
Knowing the advantages of crotalaria, the team from the IAC decided to test it in crop rotation. This system has now been used for at least 3,000 years, and, today, the specialists are unanimous in saying that alternating between the planting of different species in the same area really does contribute towards improving the physical, chemical and biological conditions of the soil. Another benefit is that it reduces the incidence of pests and diseases in the crop. This is because plants from the same botanical family are, generally speaking, susceptible to the same pests. So, when one alternates, by the planting of species from different families, one breaks the cycle of these plant’s natural enemies, which, without food, can not survive until the previous crop is introduced once again.
In spite of crop rotation being no novelty, information on the handling of grain in the soil of São Paulo is not always welcomed. Hence the importance of the research by the IAC, which took into consideration areas that are representative of farming in São Paulo to test the models. Two experimental fields were installed in the northeast of the state, in the municipalities of Votuporanga and Pindorama, and one other in Mococa, in the north of the state, on the border with Minas Gerais. These two agricultural areas, although they have soils with very different characteristics, show some similarities, such as a deficiency in limestone, an element that is essential for correcting acidity in the soil and one of the causes of low productivity in the crops. The degradation of the land caused by decades of inadequate handling is another point in common between the three fields tested.
Funded by FAPESP, the research extended over three farm harvests: 1999-2000, 2000-2001 and 2001-2002. The experimental fields were given the necessary manuring, and the seeds of soya, corn and rice used were tolerant to the acidity of the soil. The areas were divided into plots, where the possible combinations between the crops were tested, with and without planting Crotalaria juncea in the winter. Furthermore, they set aside land for growing corn, rice and soya without rotation.
In all the situations analyzed, the results showed that the crops of corn and rice, grown after crotalaria, performed better than the others, as far as productivity and the size and quality of the grains was concerned. Crop rotation also proved to be the best option for cultivation. “This project confirmed my earlier works on the importance of rationalizing the use of the soil. Legumes have an essential function in this direction”, says Mascarenhas.Accompanying the behavior of soya in the field, and without failing to take into account its properties for fixing nitrogen in the soil, in 1977 the researcher started a job that lasted about ten years. Mascarenhas and colleagues from the IAC noticed that the residues of nitrogen in the soil would increase with year’s planting of soya. With this finding, they set out for the tests, rotating soya with corn, rice, wheat, sorghum and sugarcane.
The research demonstrated that the need for nitrogen can be fully met as soon as the first year’s rotation with soya. According to the researcher, 1 hectare (an area of 10,000 square meters) of soya planted fixes an average of 160 kilos of nitrogen per hectare, while rice, wheat, sorghum and sugarcane need 200 kilos of ammonium sulfate per hectare. One hundred kilos of this product costs the farmer R$ 52. More demanding, corn needs between 300 and 600 kilos of fertilizer to cover the same area. In all cases, different quantities of chemical fertilizer were applied, with an increased share in feeding the plants, year after year.
“The data showed us that, in the areas with rotation with soya, this nitrogen did not result in an increase in productivity, which proves that it was not necessary”, Mascarenhas advises. Even though this research was concluded at the end of the 80’s, it continues up to date. Especially at a time when soya has become Brazil’s great export product, and using it in rotation with gramineae like rice, corn and sugarcane can bring the farmer some extra income.
Effects of Crop Rotation and Green Manuring on Parameters of the Soil and Productivity of Rice, Corn and Soya (nº 99/00491-5); Modality Regular line of grants for research; Coordinator Hipólito Assunção Antônio Mascarenhas – IAC; Investment R$ 36,953.00