Background
The development of recommendations for the correction of soil fertility in the Cerrado, on economic bases and based on its chemical and physical analyses, was one of the main missions of Embrapa Cerrados, a unit of the Brazilian Agricultural Research Corporation created in 1975.

Soil acidity and the generalized deficiency of nutrients, mainly phosphorus, were the main limiting factors to agricultural production in the region. The economic doses of phosphorus for annual crops in open areas of the cerrado proved to be superior to the fertilization recommendations adopted until then. Based on experimentation in soils with different clay contents, the first recommendations for corrective phosphate fertilization (phosphating) were generated in the early 1980s.

Doses varying from approximately 100 to 250 kilograms per hectare of diphosphorus pentoxide, in the form of soluble sources, applied in the total area and incorporated into the soil in the first year and supplemented with annual doses in the sowing line, were shown to be necessary.

With the widespread adoption of no-tillage in the region from the mid-1990s, new strategies for phosphorus fertilization began to be studied at Embrapa Cerrados through long-term experiments. The results showed the viability of annual maintenance phosphate fertilization by broadcast in pre-planting of soybeans and corn, replacing fertilizer in the sowing line, in soils with adequate (corrected) levels of phosphorus, a practice now adopted in more than half of the area cultivated with these crops in the Cerrado, streamlining planting operations.



Sugar cane
With the great expansion of the sugar and alcohol sector in Central Brazil in the last two decades, Embrapa Cerrados started in 2008 a broad research program in sugarcane. The management of phosphate fertilization was one of the main subjects studied. It was based on the knowledge generated in the unit for annual crops, as well as on the review of the published results of experiments on sugarcane phosphate fertilization carried out by different institutions.

The first experiments were installed in 2009 at the Goiasa, Anicuns, Jalles Machado and Vale do Verdão plants in the state of Goiás, at Destilaria Veredas and at the Usina WD in Minas Gerais, and at Usina Pedro Afonso in Tocantins, in addition to experiments in Brasília. Currently, experimentation and other studies are being carried out at the plants of the São Martinho group in São Paulo and Goiás, and at Embrapa Cerrados.

The experimental results confirmed the economic responses to corrective phosphorus fertilization, complementing the fertilization in the planting furrow in soils with low availability of phosphorus, with a residual effect over five cuts and productivity gains of stalks per cut, ranging from approximately 5 to 20 tons per hectare.

These gains are explained not only by the additional dose of phosphorus in the corrective fertilization, but also by the high efficiency of use by the culture of the phosphorus incorporated in the total area. The possibility of replacing the phosphorus fertilization in the planting furrow was shown, applying the entire dose of phosphorus in a broadcast with incorporation.

The experimental results revealed higher or similar yields with superphosphate at high doses (greater than 150 kilograms per hectare of diphosphorus pentoxide) applied by broadcast with incorporation compared to the same doses in the planting furrow . In experiments at the Goiasa and Jalles Machado plants, a high response to phosphate fertilization of ratoons was also verified in soils with low phosphorus availability, fertilized in the planting furrow, but without corrective fertilization.

Under these conditions, annual culm productivity gains of up to approximately 20 tons per hectare were observed, with annual doses of 40 kilograms per hectare of diphosphorus pentoxide applied on the straw in the crop rows. The presence of abundant superficial roots at the soil-straw interface explains the high efficiency of use by sugarcane of superficially applied soluble phosphorus.

Productivity gains with phosphate fertilization of stumps, less pronounced, were also observed in the presence of corrective fertilization. A surprisingly large increase in productivity with phosphate fertilization of ratoons was observed in an ongoing experiment at Embrapa Cerrados, in soil with very low availability of phosphorus, fertilized at planting with 200 kilograms per hectare of diphosphorus pentoxide at the bottom of the furrow.

The application of another 200 kilograms per hectare of diphosphorus pentoxide in the form of triple superphosphate in bands after the third cut provided a productivity gain of approximately 40 tons per hectare of stalks already in the fourth cut, with increases observed in all yield components ( number of stalks per meter, length and thickness of stalks).

The rapid and pronounced response of the crop to this fertilization shows the viability of “ stub phosphate ” as an opportunity to recover sugarcane productivity when phosphorus availability is the limiting factor, with the expectation of a residual effect in the subsequent reform.

Alternative sources were also studied. The filter cake evaluated in experiments at the Jalles Machado and Goiasa plants and at Embrapa Cerrados proved to be equivalent to superphosphate when applied at the same doses of total diphosphorus pentoxide. Imported natural phosphate of high reactivity (high solubility in citric acid) proved to be equivalent to superphosphate when applied to broadcast with incorporation in soil with hydrogen ion potential (in water) below 6.0, this performance being superior to that verified in previous experiments in the first year with annual crops.

A significant loss of efficiency was verified for the same phosphate in an experiment at the Veredas Distillery in soil with a hydrogen ion potential greater than 6.5. In localized application, at the bottom of the planting furrow, the phosphate efficiency was low in both experiments. The negative effect of concentrated application it also explains the low efficiency as a source of phosphorus of a granulated organomineral fertilizer based on filter cake and highly reactive natural phosphate, evaluated in an experiment at the Jalles Machado plant.

Brazilian natural phosphates classified as reactive and other alternative sources of phosphorus are being evaluated at Embrapa Cerrados. Sampling studies of sugarcane soils are in progress at the São Martinho Group mills, with the following objectives:

a) define the minimum number of subsamples necessary to compose the sample sent to the laboratory;
b) know the effect of the sample position in relation to the crop line on fertility attributes at different depths.

Of the main attributes, phosphorus and potassium are the ones that show the greatest variability, even on a scale of small areas in mesh sampling, requiring a greater number of subsamples than has been adopted by mills in general to characterize the availability of these nutrients.

Agricultural research is continuous work, in which many recommendations require updates in line with the evolution of cropping systems. A recent publication with recommendations for phosphate fertilization of sugarcane in the Cerrado contemplating the traditional cultivation system, irrigated cultivation and the no-tillage system in sugarcane field reform can be accessed on the Embrapa Cerrados page.