Soil management for sugarcane

The expansion of sugarcane cultivation in areas where soils with a light textured surface horizon predominate, in the Center-South region of the country, has caused worrying soil degradation processes, with these soils being more susceptible to erosion.

On the other hand, clayey soils may have greater compactness, or reaction to machine traffic and overflows, than sandy soils, being subject to increased density and decreased porosity, which harms plants and their root development.

The effect of the reform period and the use of economic crops (oilseeds - soybean, sunflower or peanuts and grasses -, sweet sorghum, corn) and soil recovery crops (brachiaria, green manures) will be observed. The physical, chemical and biological behavior of the soil and its capacity for self-recovery and production should be evaluated, taking as reference areas under natural vegetation, long-term pastures and annual and perennial crops managed with conservationist systems.

Meiosi (simultaneous interrotational method), with intercropping, which allows mother lines of sugarcane to be left in the field, and therefore the seedlings, will enable the replacement and rotation of crops in the location, where the predecessor crop is soybeans, for example.

Description of activities

The use of ratoon crops, as a way of facilitating the incorporation of fertilizer into the soil and leaving the land in favorable conditions for the application of herbicides in places where there is no straw, makes the soil more suitable for management and preparation.

The purpose of soil preparation is to make the land ready and suitable for the next activity in the production chain - the planting process - to be carried out. It includes activities normally carried out according to an operational sequence, sometimes quite standardized.

Operational sequence

The choice of type of preparation will depend on the characteristics of the soil in each location where the management will be carried out. Harrowing is an operation used to build roads, as it allows the soil to become compacted when used with excessive soil moisture, forming preparation scars. The extensive use of harrowing at the same depth does not improve water infiltration or promote soil aggregation. However, harrowing combined with subsoiling and plowing can have benefits, if well regulated and used at the appropriate time.

The certainty that poorly managed soils can irreversibly lose their productive capacities underlies the importance of the resilience of tropical soils. This leads farmers to seek to minimize potential damage that may be caused to soils due to the lack of agronomic care in their use for agricultural production.

Definition and use of conventional preparation

Heavy grading: This same operation must be carried out again in the final phase of conventional soil preparation, with the aim of reducing, as a priority, the size of the blocks left by previous operations (construction of terraces, subsoiling and plowing, if applicable) and incorporating any crop remains that still remain on the surface of the land.

Light harrowing and interaction in management with herbicides: When used to complement the second heavy harrowing, it is intended to break up the soil, leaving the surface level for furrowing. For the operation to be effective in assisting herbicide products, it must be carried out at most one or two days before furrowing. This is justified because seeds, especially grass seeds, when germinating, send out their root primordia in the direction of the soil depth and, after one or two weeks, the root absorption products can no longer have the expected effect in controlling weeds. After this time, the roots are no longer within the range of action of the herbicide products and the weeds vegetate without limitations.

Intensive mechanization

Morphological and, consequently, physical-hydraulic attributes are extremely relevant to the management and conservation of soils in sugarcane cultivation, since, together, they affect the speed of water infiltration (hydraulic conductivity), its storage capacity, the resistance of aggregates to destabilization, or the stability of aggregates, and the available water.

The average water deficit values ​​for some locations in the Center-South region are shown in the figure. It should also be noted that these deficits are calculated based on monthly data, which significantly mask the real deficits.

Third axis matrix

The third axis matrix is ​​due to a new strategy developed by the IAC, by bringing the production cycle, that is, the cutting of sugar cane, as another factor, the third, to be added to the production environment and the harvest season, with the objective of minimizing the effects of the water deficit.

This effect of minimizing the water deficit consequently generates more expressive and immediate gains in productivity, especially in the second cut and in the most advanced cuts in the sugarcane field. This is because this model directly impacts the deepening and development of the roots, causing a decrease and even an increase in the stalk population in these first cycles.

The question of argisols

Considering the soils of the western region of São Paulo, they can be defined, in ascending order of susceptibility to erosion: LV ˂ PV arenic ˂ PV. Regarding preparation (Table 1), they should be allocated, when necessary, in periods of greater rainfall, allowing the preparation of argisols to be directed to months of less intense rainfall. In regions with more pronounced water deficit, latosols should not receive sugarcane planting in January/February, exceptionally when eutrophic, since, due to the low CAD and significant development until May/June, even implying the formation of the first internodes, they will be exposed to high water deficits in the middle of the harvest.

In this composition of soils developed from sandstones, the sandy argisols, which have lower erodibility than the argisols with a thinner A horizon, should be used for the beginning of planting. The figures show some images of profiles of sandy argisols with an abrupt character and sandy texture in the A horizon and medium in the Bt horizon, and images of the micromorphology of these profiles.

It is observed that, between the A + E and Bt horizons, there are medium-textured lamellae (15% to 20% clay), which partially interrupt drainage; in Bt, there are water accumulation zones, due to structural weakness (average clay content between 15% and 25%), with no continuity of the pores, resulting in high amounts of available water due to the lack of drainage of this Bt horizon, classifying these profiles as high CAD soils and, therefore, their harvest period should be extended, both to the beginning and to the end of the harvest.

It should be remembered, however, that susceptibility to erosion is a function of hydraulic conductivity and the resistance of aggregates to dismantling and washing away by water (Morgan, 2005), and that these argisols are presented without aggregation in the A horizon (single grains, normally quartz). Thus, although arenic soils present high hydraulic conductivity, only one phase of resistance to erosion requires plant cover to promote the binding of sand by the root system of this cover (sugar cane ratoons, crotalaria, millet, weeds, etc.), which produces a temporary “structure” sufficient to prevent dismantling and the consequent washing away of individual quartz particles.

* By Sandro Roberto Brancaliao, Marcos Guimarães de Andrade Landell, Marcio Aurelio Pitta Bidoia, Raffaella Rossetto, and Mauro Alexandre Xavier (IAC)