Soil Acidity Management and Liming Practices.

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The success on soil acidity management does not only depend on the basic acknowledgement about acidity theory and amendment characteristics. The liming practice involves a combination of
operations linked to limestone distribution and incorporation, and those are equally important. The liming does not work if doses of the amendment are incorrectly applied on soil due to improper
spreader equipments or if they are bad regulated, even if the correct theoretical basis has been calculated. Thus, the uniformity on application, grade of mixture of limestone particles on soil and
the depth of penetration are critical to liming success.

As a basic rule, it´s said that it´s much better if the amendments are deeply mixed and incorporated to soil. With this, limestone reaction is quicker, once the products of amendments reaction will be rapidly consumed by soil acidity and the correction on subsoil layers allow a deeper anchoring of plants. And this allows a better productivity and stabilization of production.

The worst is that in past few years, Brazilian producers are getting more interested on conservative managements of soil like reduced preparation and, mainly, the direct crop. These systems have the
lowest possible mixture of soil which affects, directly, the liming practice at a point that the limestone is applied to soil surface without incorporation (it happens in cases of direct crop).
This chapter shows an overview about these subjects, emphasizing the most relevant aspects of agricultural productivity.

Limestone distribution.

The distribution of the acidity amendment must be as much uniform as possible, at any soil management system. It´s easy to note when limestone are not uniformly distributed in highly acid soils because the plants grow irregular through the field. In low-level acid soils also have negative effects, but it´s more complicated to observe.

The uniform limestone distribution depends on the quantity and the regulation of spreader equipments. It´s necessary to have correct sized equipments in function of property size and also that farmers become aware about equipment limitations in order to minimize heterogeneity on applications.
There are different limestone spreader models in Brazilian market, in which details can be obtained on the texts written by Mialhe (1986) and Dallmeyer (1986).

An important aspect is the operator to domain the dosage mechanisms and the technical briefing of equipment regulation, in order to adjust the recommended doses for each lot of limestone purchased. This makes necessary because the products have different particle densities and wide moisture variation. All this interferes on the dosage application. It´s also important to know the distribution range or the equipment transversal profile.
It describes limestone quantity that spreaders will distribute in function of the distance from the machine axes, on the transversal way to farm tractor displacement. Except the spreader machines known as trough, that uses gravity to distribute the limestone in the direction of its width extension, the other spreaders have devices to throw limestone particle farther, fact that increase the range of application and consequently increase yield of application.

It means that the higher particle concentration is near to spreader axe compared to the edges range of application. For this reason, it´s necessary to overlay the application zones to get a better uniformity. The equipment catalogs, usually, promises wider zones then the reality, like until 14 m, what results on a very big lack of uniformity. It´s essential that farmers do not exceed 8 m of application zone, in order to have a better uniformity.

An additional care must the taken about the Spinner-style lime spreaders because they have only one distribution rotor. These ones have an asymmetric transversal profile that increases the lack of uniformity distribution of the particle.

Limestone local application.

In the past, some Brazilian farmers (mainly those who made land leasing) tried to reduce liming costs by applying small quantities of limestone on crop holes. Some machines had been produced with three tanks. At that time, scientific researchers had been made and it was shown that this kind of job was not effective, especially on highly acidic soils (Ben et al., 1981).
The data shown in the box say that crops corresponded to this kind of liming, but not on the area that received the liming type called "launch". Additionally, in this condition the productivity average
remained low for four years. There is no additional effect in soils that receive the in line liming on the correct doses of limestone, on the overall area. (Ben et al., 1983).

Another research, with similar aim, was developed by Nakayama et al. (1984) in savanna's soil in the State of Mato Grosso do Sul.
The results were shown on box 5.2. At first sight, the increase on
soy production by applying limestone on crop holes are beneficial, once the application achieved 3,000 kg/hectare of soy, considering four harvests. By the other side, the economic analyze show
short gains, mainly on the first two years. And these two years are the most important to producers that lease a land1, once the leasing period is too short. In the remaining years, limestone doses hav accumulated on soil and as crop holes change each year, the result is a overall area limed, but with low cost/benefit ratio. Additionally, the in line liming let the crop operation more complex and with a lower yield once the machines need to be refueled all the time.

Another type of limestone local application also occurs on permanent crops in which the fertilizer applications are made on sides next to the plants, causing higher soil acidification. When it happens, farmers can correct it by making the local liming in order to reduce heterogeneity and save limestone. In this case, it is necessary special equipment for this kind of application. It is possible to reduce until 30% the limestone dose per area.

Jose A. Quaggio
Acidity and liming on tropical soils
Agronomic Institute. Campinas-SP

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