RESEARCH WORK

Effect of tillage systems on Luvisols dedicated to pasture production

Santa L. Leyva¹, A. Masaguer² and Aimé Baldoquin ¹

¹ Universidad de Las Tunas, Carlos J. Finlay s/n, Rpto. Santos, Las Tunas
²Universidad Politécnica de Madrid, España
E-mail: laural@ult.edu.cu

ABSTRACT

A trial was conducted in order to determine the influence of tillage systems on the properties of Luvisol soils, in the Las Tunas municipality. The evaluated indicators were: apparent density (ñ_b), total porosity (Pt), porosity of aeration (Pa), organic matter (OM) and Oligochaeta density and biomass. Experimental units were sampled, in a split-plot design and three repetitions, at the depths of 0-5, 5-20 and 20-30 cm. The OM contents and the Oligochaeta density and biomass were evaluated up to 20 cm. Two systems were considered: traditional tillage (TT) and tillage without turning up the soil layer (TWT) compared with a control without tillage (NT). The TWT produced the lowest density and the highest quantity of porous spaces in the soil matrix, with values that differed significantly from TT and NT, and favored the development of Oligochaeta up to the depth of 20 cm. The maintenance of the dense layers in the depth 20-30 cm in the TT decreased the total porosity and restricted root development, with aeration porosity values much below 10 %. It is concluded that traditional tillage affected the OM content at short term, and maintained the compact layers in the underlying horizon, for which the continuity of this practice in the livestock production areas of the region is not justified at short or long term.

Key words: Pasturelands, soil management, Oligochaeta.

Among agricultural practices, the most important one is tillage. If it is known what problem is to be solved, it leads to soil and agriculture sustainability; otherwise, it brings about degradation (Amézquita, 1998). One of the factors that cause physical degradation is compaction, considered as the main cause of soil degeneration (Pagliai et al., 2003).

At present, the conservationist preparation systems, which preserve the soil and the environment, are highly important (Albiero, Da Silva-Maciel and Tunussi, 2011). To achieve sustainable development, the selection of more adequate technologies in each case, and in every moment, is essential. The purpose is for the soil to reach ideal conditions for root growth, which is related to the tillage systems (Osuna-Ceja et al., 2006).

The soil turning caused by traditional tillage increases the flow of CO₂ to the atmosphere, and as a consequence it decreases the OM content (López-Garrido et al., 2009); which directly affects quality and fertility due to the great influence of OM on the physical, chemical and biological properties, all of them necessary for the normal development of the soil functions (Magdoff and Weil, 2004). Espinoza (2010) and López (2010) reported a carbon loss in the soil where traditional tillage was used with regards to conservation tillage.

The modern or mouldboard plow is one of the main causes of soil degradation, serious problem faced by current agriculture. Its use, as well as that of other farm implements has provoked many environmental quality problems (Huggins and Reganold, 2008). Osorio et al. (2009) state that vertical tillage favors the soil conditions for the conservation and good utilization of that resource, and it consists in decreasing operations with regards to conventional tillage, without turning the soil over.

In Cuba one of the main causes of yield decrease is soil compaction and the presence of hardened (thickened) layers which causes negative effects on root growth. Studies have been conducted indicating that the use of plowing plus harrowing or their combination with other operations constitute a choice for pastureland recovery (Martínez, 2000; Padilla, 2002). On Ferralitic soils, when rehabilitating a Guinea grass (Panicum maximum) pastureland, Crespo et al. (2006) proved that plowing plus harrowing produced a better effect, because the yield and covered area percentage increased; while subsoiling favored the size of stable aggregates. However, in Luvisol soils no studies have been reported of the influence of tillage systems, for which the objective of this work was to evaluate the effect of tillage without soil turning and of conventional tillage on the properties of such soils, in systems of improved or cultivated pastures.

MATERIALS AND METHODS

Location, design and treatments. The study was conducted in 2012, in a short-duration essay, at the livestock production farm La Veguita located in the northern zone of Las Tunas municipality, Cuba-. An area of Pennisetum purpureum CUBA CT-115, sown in 2007, was selected which showed less than 30 % of cover by the crop due to its inadequate management. The experimental design was split plots, with three repetitions. Two systems were considered: traditional tillage (TT), performed with ADI-3 plow, at a depth of 20 cm, followed by two harrowings; and tillage without turning over the soil layer (TWT), performed with a MAU-250 C multi-plow for turning and crossing at 30 cm of depth, with an intercalated harrowing and another one after crossing, which were compared with a control without tillage (NT). The plowing and crop sowing were performed with oxen.

Procedure and measurements. The procedure and measurements were carried out in May, 2012, six months after the soil preparation was finished. The apparent density r_b (five samples in each experimental unit) was evaluated at three depths (0-5, 5-20, 20-30 cm), with the cylinder method; and the total (Pt) and aeration porosity (Pa) were determined by calculation (Cairo, 2003). The OM was evaluated at two depths (0-5 and 5-20 cm), through the method proposed by Walkley and Black (1934), and 10 soil samples were taken in each of the areas at the depths of 0-10 and 10-20 cm to determine Oligochaeta density and biomass, according to Anderson and Ingram (1993).

Statistical analysis. The statistical analysis of the data was made with the statistical pack SPSS® version 15.0 for Windows. The main stadigraphs (arithmetic mean and standard error of the mean) were determined. The data showed a normal distribution and were subject to a variance analysis (ANOVA). The mean comparison was made through Tukey's test (p < 0,05).

RESULTS AND DISCUSSION

The effect of the tillage systems on apparent density (table 1), in the first 5 cm, did not show significant differences between them, but they did differ from NT. Between 5 and 20 cm the TWT caused the lowest density and differed from TT and NT. From 20 cm the influence of TWT was more effective, with adequate density values, and differed significantly from TT and NT. This proved that the plowing with discs performed in the TT did not go deep, and therefore high compaction was maintained in the deep layers. According to Hernández et al. (2006), the soils with intensive cultivation show high density values in the Bt horizon, with the formation of a plowing floor, when no subsoiling operations are carried out in a long-term period.

These results proved that the apparent density is a good indicator to evaluate the physical quality of a soil, at short term, in different management systems.

Total porosity increased in both tillage systems (table 2) in the surface soil layer (0-5 cm), without differences between them, when comparing it with the mean values obtained before disturbance (NT). At the depth of 5-20 cm the TWT showed high values and differed from the other treatments, and at the depth of 20-30 cm the differences were significant, with higher values in the TWT; while the TT and NT did not differ from each other.

This indicates that the TWT produced the highest quantity of porous spaces throughout the soil matrix, with values that differed significantly from TT and NT. The maintenance of the dense layers at the depth of 20-30 cm in TT decreased total porosity and restricted root growth, with values of aeration porosity below 10 %.

These results showed that TWT favored the structural quality of the soil, as stated by Osuna-Ceja et al. (2006). In Colombia, in the eastern plains, Amézquita et al. (2004) found a rapid deterioration of the physical properties, when the disc plow and the cultivator were intensely used. The changes in the physical properties affect the surface condition of the soil, which causes an increase of erosion, with the subsequent loss of thickness of the surface horizon (Prieto-Méndez et al., 2013).

The effect of tillage systems on the OM content is shown in figure 1. The TWT did not show significant differences from treatment NT, but it did from TT, at the evaluated depths. TT up to 20 cm of depth increased total and aeration porosity, which influenced the decomposition of organic residues, a higher oxidation of the OM and a decrease of 0,4 % of its content.

In addition, the breaking down of aggregates and the susceptibility to disaggregation due to erosion were stimulated. Tivet et al. (2013) showed that the physical protection of the most labile SOM fraction due to aggregation is not sufficient in soils where conventional tillage is applied, and observed a general depletion of the functional carbon groups.

Espinoza (2010), when evaluating the effect of three tillage systems, found a 4 % decrease of OM with the use of conventional tillage and 19 and 6 % increases in direct sowing and minimum tillage, respectively. On the other hand, López (2010) studied conservation tillage at short term and found a carbon loss in traditional tillage with regards to conservation tillage, especially in the first 10 cm of soil.

The average density of Oligochaeta for the depth of 0-10 cm varied between 18,3 and 75 individuals/m², without differences between treatments NT and TWT, but they did differ from TT which showed the lowest values (fig. 2). This result is ascribed to the fact that in TWT, the soil disturbance was lower and the edaphic fauna was protected with the residues on the surface. In the stratum of 10-20 cm TT and TWT favored the development of Oligochaeta, but there were differences between them and the highest values were found in TWT. In this sense, Masín, Rut and Maitre (2011) found in a site with conventional tillage a scarce number of Oligochaeta, due to the low organic matter contents and the permanent disturbance of the soil.

The biomass of Oligochaeta had a similar performance as that of density, for both strata. NT in the layer of 0-10 cm showed the highest values, but from 10 to 20 cm no Oligochaeta were found; nevertheless, the decompaction in that layer with both types of tillage favored water and air flow and the activity of the macrofauna, and the highest values were reached in TWT. In studies with different use and tillage systems performed by Botina et al. (2012), they found that the highest Oligochaeta biomass and abundance appeared in the least disturbed soils, and traditional tillage showed the lowest value in general; it reaffirms that Oligochaeta biomass is a potential tool as bioindicator of soil quality.

The changes in the soil properties with the different tillage systems indicated the evolution of its quality and show the positive effect of TWT, which can also represent an alternative for carbon sequestration in the soil and improve its functioning.

The results showed that TT based on plowing and harrowing affected the OM contents at short term, and maintained the compact layers in the underlying horizon, unfavorably influencing the air and water flow and the root growth of the pastures, for which the continuity of this practice in the livestock production areas of the region is justified neither at short nor at long term. The TWT produced the lowest density and the highest quantity of porous spaces in the soil matrix, and favored the development of Oligochaeta up to the depth of 20 cm.

Received: March 20, 2014
Accepted: June 10, 2014