Soil compaction is a common problem of mineral soils under
conventional tillage practices. Organic matter addition is an efficient way
of reducing the effects of field traffic in soil compaction. The aim of this
study was to investigate the effects of number of tractor passes (one, three, and
five) on depth-dependent (0–10 and 10–20 cm) penetration resistance, bulk
density, and porosity of clay-textured soil (Typic Xerofluvent) under
organic vegetable cultivation practices in the 2010–2013 growing seasons. Fields were treated
with farmyard manure (FYM, 35 t ha
Agricultural development resulted in the increase in the food supply for humankind, but it also resulted in the increase in soil and water losses, reduction of the vegetation cover, and degradation of the soil (Cerda, 2000). One of the consequences of agricultural use and abuse is the increase in soil compaction. Soil compaction, which can be defined as a soil degradation process in which an applied pressure to the soil causes soil grains to get closer together, resulting in reduction of porosity and pore volume ratio, is regarded as the most serious environmental problem in conventional agriculture (McGarry, 2003). Since farmers have difficulty locating and rationalising this type of degradation without making any measurements, this problem can be more deleterious in conventional agriculture. In addition, compaction-induced shallow plant rooting and poor plant growth reduce crop yield for deep rooting plants and vegetative cover, which protect soil from erosion (Ni et al., 2015; Ola et al., 2015; Shaw et al., 2016). Compaction can increase run-off from and erosion of sloping land or waterlogged soils in flatter food slopes, depending on reduced water infiltration through soil surface (Al-Dousari et al., 2000; USDA-NRCS, 2012; Pulido et al., 2016). Intensive agriculturally-related soil compaction may be regarded as one of the significant reasons for land degradation (Cerda, 2000; Barbero-Sierra et al., 2015; Wang et al., 2015; Yan et al., 2015) and the elevated risks concerned with food security, water scarcity, climate change, biodiversity loss, and health threats, which were pointed out as soil-related challenges for a sustainable society (Keesstra et al., 2016).
The most significant cause of soil compaction is field traffic. Meanwhile, the close relation between field traffic density and frequency and crop type should also be taken into account (De Oliveira et al., 2015; Gelaw et al., 2015). Thus, more than 80 % of corn and soybean fields is under tyre pressure in a growth season (Erbach, 1986). In cereal cultivation, 90, 35, and 60 % of fields are under wheel pressure during seed bed preparation, harvesting, and baling practices respectively (Munsuz, 1985). Soil aeration, infiltration, and hydraulic conductivity parameters of soils, which are closely related to differential porosity, show decreases related to increased field traffic (Seker and Isildar, 2000; Aksakal, 2004). In order to prevent such adverse effects, decreased field traffic along with optimum moisture content of tillage soil, and increase in the organic matter content of soil using farmyard manure, compost, green manure, etc. Stabilisation and fortification of soil aggregates using organic matter can increase compaction resistance of soils (Cochrane and Aylmore, 1994; Thomas et al., 1996; Aksakal et al., 2016) and enhance the compaction-related attributes such as bulk density, pore-size distribution, infiltration, etc., in soils (Sparovek et al., 1999; Carter, 2002; Aksakal et al., 2016). The changes in soil organic carbon stock under different management systems (Munoz et al., 2015) can also influence total soil quality in soils. For example, Parras-Alcantra et al. (2015) reported a higher organic-farming-induced stratification ratio deeper in the surface horizon compared to conventional agricultural systems. Gelaw et al. (2015) pointed out that managing soil differently affected the partition of organic matter in different aggregate sizes, which in turn influenced bulk density and water-stable aggregates. Although the specific effect of field traffic was not elucidated in these studies (Gelaw et al., 2015; Parras-Alcantra et al., 2015), the management systems are closely related to traffic density and soil physical attributes. The organic matter is relevant to soil behaviour, but it is also relevant at the atmospheric level and to the behaviour of the earth system since it can control the carbon cycle (Novara et al., 2013; Kaleeem Abbasi et al., 2015; Peng et al., 2015).
Chemical and physical properties of experimental soil and FYM (Uzumcu, 2016).
Porosity, bulk density, and organic matter content of the plots before passing.
Keesstra et al. (2016) pointed out the significance of raising public and farmer awareness about key attributes of soil organic matter to perform and sustain ecosystem services. Similarly, many researchers reported that soil physical and chemical properties in terms of fertility and sustainability of agriculture may be enhanced, to a large extent, by regular organic matter application (Aggelides and Londra, 2000; Alagoz et al., 2006; Mamman et al., 2007; Celik et al., 2010; Gulser and Candemir, 2012). The above-mentioned literature points out that the nature and extent of compaction-induced soil degradation can be exaggerated by a lack of organic matter. Artificial loosening of soils by deep ripping is a commonly suggested practice for elimination of the deleterious effects of compaction, but its effect is not long-lasting (Hamza and Anderson, 2003, 2008; Arslan, 2006). Organic matter addition is a fast and efficient way of conditioning soil physical attributes, especially soils that develop in a xeric environment. Despite the fact that the effect of organic matter on soil fertility and soil properties has been frequently investigated, there is a lack of information about comparative effects of continuous application of farmyard manure and green manure on soil physical attributes of soils that develop in a xeric environment suffering from a lack of organic matter under organic vegetable farming. Therefore, the aim of this study was to investigate the effects of both annual addition of different organic matter (farmyard manure and green manure) and field traffic density on penetration resistance, bulk density, and porosity in clay-textured soil with low organic matter content after 4 consecutive years of organic vegetable cultivation.
The effect of number of passes on penetration resistance
at different depths (passing
Main effects of organic matter incorporation, depth, and number of passes on measured parameters.
Different letters in the same column indicate differences at
This study was carried out on an experimental field of the Agricultural Research and Application Centre of Suleyman Demirel University from 2010 to 2013. Chemical and physical properties of the soil are given in Table 1.
Organic vegetables were cultivated with farmyard manure (FYM), green manure
(GM), and conventional tillage (CT) without any organic matter
treatments. The field experiment was set up with a completely randomised design
with three replications. FYM application was executed between 21
May and 7 June on 35 t ha
The data were subjected to descriptive analyses in order to check normal distribution. Aside from compaction data sets, all parameters measured showed typical normal distribution. The compaction data were log-transformed before analysis of variance (ANOVA) using Minitab 16 statistical package programme (Minitab, 2010). The mean separation between the treatments was performed using a least significant difference (LSD) test at 95 % confidence level.
Number of passes and soil depth-dependent bulk density changes
induced by organic matter treatments (passing
Number of passes and soil depth-dependent total porosity changes
induced by organic matter treatments (passing
The application of FYM and GM for 4 subsequent years significantly reduced penetration resistance in both depths; however, the effect of FYM treatment was higher than GM treatment (Fig. 1, Table 3). This finding is in accordance with the previous studies (Celik et al., 2010; Gulser and Candemir, 2012; Xin et al., 2016). Incorporation of organic matter in clay-textured soils can strengthen the aggregates by weakening cohesion forces and interfering with the formation of crust and large aggregate (Aksakal et al., 2012). The larger amounts of added organic matter may mediate the formation of clay–organic matter complexes, which in fact reduces the penetration resistance on the one hand and protects organic matter against microbial decay on the other hand. In this respect, Blanco-Moure et al. (2016) investigated the effect of soil texture on carbon and organic matter distribution among different fractions under different tillage and management practices. They found that soil clay had a critical role in the chemical stabilisation of organic matter through clay–organic complexes in the soils. Czyz and Dexter (2016) pointed out the relation between the magnitude of clay–soil complex and the porous and open nature of the structure. Thus, stable organic matter sources such as FYM resulted in desirable penetration resistance (< 2 MPa) for plant growth under changing field traffic.
Number of passes and soil depth-dependent microporosity changes
induced by organic matter treatments (passing
Number of passes and soil depth-dependent macroporosity changes
induced by organic matter treatments (passing
The increasing number of passes, irrespective of the organic matter treatments and soil depth, increased soil compaction measured by penetration resistance (Table 3). The effect of field traffic on penetration resistance, as expected, was more negative in 0–10 cm depths (Table 3). Accordingly, Carman (1994) and Seker and Isildar (2000) determined a higher compaction ratio in the 0–10 and 0–15 cm surface layers respectively. A penetration resistance value as high as 3.60 MPa in the surface layer caused by five passes in the control treatment (Fig. 1) with no organic matter may have significant inverse effects on infiltration, percolation, and run-off-induced erosion under intensive precipitation events in slopy lands (Kozlowski, 1999; Seker and Isildar, 2000). In this study, we also determined the well-known manner in which surface soil becomes more compact with field traffic, and the severity of the problem may be overcome by adding organic matter to soil or by adopting soil management systems with decreased annual traffic. The penetration resistance value at 10–20 cm depth obtained for CT and GM treatments after five passes was over 2 MPa, which is considered the limit value by the USDA (1993) as a critical physical quality parameter in conventional agricultural practices. This critical value can change depending on the soil tillage systems. For example, with minimum tillage practices where a chisel is used for soil tillage it is 3 MPa and with no-till practices it is 3.5 MPa (De Moraes et al., 2014). The critical penetration resistance value that inhibits root development is accepted as 3 MPa (Busscher and Sojka, 1987; Hakansson and Lipiec, 2000; Aksakal et al., 2011). Soil management systems can change soil organic carbon contents (Munoz-Rojas et al., 2015) and field traffic density, which ultimately degrade soil physical traits for optimal plant growth such as water-stable aggregates and bulk density (Gelaw et al., 2015). In fact, these tendencies of soil physical traits can lead to more compaction in both the surface and subsurface soil layers, as in our case.
The main effect of organic matter treatments on bulk density was
statistically significant (
The main effects of organic matter incorporation, depth, and number of passes
on porosity were significant (Table 3). The effects of treatments, in
relation to soil depth and field traffic density, on porosity in descending
order were FYM > GM > CT. The main overall effect
of depth on total porosity was detrimental at 10–20 cm depth where a
significant decrease was observed. The initial average
(0.565 cm
Macroporosity, which is critical for soil aeration and soil water
circulation, was changed as a function of soil depth, field traffic density,
and organic matter amendments (Table 3). The main effect of organic matter
was FYM > GM > CT in descending order. In this
study, organic matter amendments significantly improved macroporosity
(
Enhancement of soil structure traits by reduction of aggregate wettability
(Zhang and Hartge, 1992) and enhancement of strength of aggregate stability by incorporation of organic matter
partially eliminated the effects of field traffic on macroporosity after 4 consecutive years of FYM and GM application. The organic-matter-bound ambiguity was attributed to type of organic matter, C
The effect of field traffic density on soil compaction was found to be dependent on addition and type of organic matter treatment. The overall effects of organic matter treatments on penetration resistance and bulk density irrespective of soil depth were in descending order CT > GM > FYM, whereas it was FYM > GM > CT for total and microporosity. Macroporosity appeared to be higher at minimum field traffic for the FYM treatment in the surface layer. It can be concluded that the use of organic matter enhances soil conditions by influencing the soil water holding and circulation characteristics, aeration, penetration resistance, and bulk density, which has implications for plant root growth.
The data of this article can be found in the Supplement.
The authors declare that they have no conflict of interest. Edited by: P. Pereira Reviewed by: two anonymous referees