**4. Liming and gypsum on clay fraction flocculation and soil particle aggregation**

Soil correction by liming and/or gypsum has a significant influence on the soil physical and water properties [9, 21–26].

Liming by applying limestone–calcium carbonate [Ca(CO3)2] or magnesium carbonate [Mg(CO3)2] is the soil management practice used to correct excessive soil acidity. In addition to correcting acidity, lime application in soils is able to provide calcium and magnesium, provide nutrients, and neutralize excess aluminum and soil manganese that are toxic to plants [20, 22].

Gypsum applied on the surface of soil columns with dimensions of 0.6 m in height by 0.3 m in diameter provided increases in Ca contents and decrease in exchangeable Al contents, consequently favoring the root growth of deep coffee seedlings [27]. These authors also pointed out that the superficial application of the gypsum–CaSO4–was more efficient than CaCO3 incorporated at 0.3 m depth due to the higher root growth in depth as a result of the exchangeable calcium increase and aluminum reduction in the subsurface ground.

In the long term, both liming and gypsum can contribute to reducing the risks of erosion in coffee-cultivated LVdf, especially under conditions without green cover between rows and with uncovered soil. In a typical Distroferric Red Latosol (LVdf) (Rhodic Hapludox), very clayey texture cultivated with coffee shrubs in Londrina, Northern State of Paraná, liming and gypsum had positive effects on soil aggregation and consequently on the water infiltration rate in the soil profile 2 years after corrective application [21].

On the other hand, the short-term incubation studies (3 months after limestone application), using samples from an LVdf from Londrina, Castro Filho and Logan [9], found that the aggregates were stable in water up to the pH value in CaCl2 equal to 5.7. On the other hand, when pH values exceeded 5.7, they reduced the stability of the aggregates in water.

*Coffee - Production and Research*

and infiltration rate.

structural elements.

and 30 g kg<sup>−</sup><sup>1</sup>

version 3.0 [16].

hydrogenionic potential determined in water.

Latosol caused by negative electric charge balance.

where PZC is the point of zero charge, dimensionless; pHkCl is the hydrogeni-

These electrochemical properties are affected by soil management and are related to soil physical properties like water-dispersible clay, aggregation indexes,

Water-dispersible colloid (WDC) is generally recognized as the fraction of clay that disperses in water. Dispersion is the ultimate state of breakdown that results in release of clay particles as a consequence of expanding double layers and dominating repulsive forces [8]. WDC is affected by the nature of soil including mineralogy [9–11], clay content and application of sewage sludges [7], soil management [8] in terms of crop sequence, application of organic manures [12, 13], soil tillage, and traffic [14] which have been shown to affect dispersion-flocculation of clay in soil

Besides liming and gypsum on coffee crop, soil organic matter may have a dispersive or aggregating effect according to the quantity and quality of the fertilizer [12]. These authors observed that the addition of manure at the doses of 23 g kg<sup>−</sup><sup>1</sup>

**3. Mechanization in crops with high coffee shrub population density**

In coffee plantations, mechanization has emerged as an alternative in reducing production costs, operating income, and reducing labor hardness. However, for the preservation of natural resources (soil and water), soil and machinery management becomes essential to minimize the effects of anthropogenic actions on the soil. Within these aspects the coffee farmers can reduce the axle load and the contact pressure of the tires with the soil and use management systems that contribute to the deposition of organic matter, as soils with greater aggregation support more load and the organic matter relieves stress exercised by agricultural machinery.

Soil stress exerted by tires or tracks of machines on soil interface can be assessed according to machine characteristics and soil attributes [15]. These authors modelled soil stress through the software Tyres/Tracks and Soil Compaction (TASC)

for the rear tire 12.4 R28 [17]. The ground average contact pressure at

TASC version 1.0 was used for the first time in Brazil in a long-term weed control method experiment to assess the effects of weed control on soil loadbearing capacity and the impact of a coffee tractor on soil stresses [17]. In this study, a coffee tractor Valmet®, model 68, with a power rating of 44.9 kW (61 hp), a total weight of 38,245 N (3900 kg), front tires of 6.16 at inflation pressure 172 kPa, wheel mass of 683 kg and rear tires of 12.4 R28 at inflation pressure 124 kPa, and wheel mass of 1.365 kg was used for coffee management and mechanical weed

soil-tire interface ranged from 101 kPa to 176 kPa, with the highest occurring for the front tires. As highlighted by Guimarães Júnnyor et al. [15], the ground average contact pressure depends on the tire type, tire structure, tire sizes, wheel load,

The contact area at soil-tire interfaces ranged from 0.0381 m<sup>2</sup>

provided dispersion of the clay fraction in electropositive *red-yellow*

∆pH = pHKCl − pHH2O (2)

); pHH2O is the

for the front tire

onic potential determined in potassium chloride solution (1 mol L<sup>−</sup><sup>1</sup>

**48**

control.

to 0.1328 m<sup>2</sup>

inflation pressure, and soil stiffness.
