Mulching effects on selected soil physical properties
Introduction
Returning crop residues to the soil improves soil quality and productivity through favorable effects on soil properties (Lal and Stewart, 1995). Favorable effects of residue mulching on soil organic carbon (SOC), water retention and percent water-stable aggregates have been reported for the surface layer (Duiker and Lal, 1999, Havlin et al., 1990). Application of crop residue mulches increases SOC content (Havlin et al., 1990; Paustin et al., 1997, Saroa and Lal, 2003). Duiker and Lal (1999) reported a positive linear effect of mulch application rate on SOC concentration.
No-till is usually associated with high levels of crop residues left on the soil surface. In Canada, mulching at rates as low as 2.25 Mg/ha reduced nutrient losses of NO3-N and available P, K, Ca and Mg (Rees et al., 1999). The effect of crop residue on soil organic matter (SOM) content is highly related to the amount and only weakly to the type of residue applied. Reicosky et al. (1995) reported a strong relationship between residue amounts and SOM in the 0–15 cm layer. Conservation of soil moisture is one of the major advantages of mulch farming system. Mulching protects the soil from water erosion by reducing the rain drop impact. A partial covering of mulch residue on the soil can strongly affect runoff dynamics, and reduce runoff amount (Findeling et al., 2003, Rees et al., 2002). Straw mulch increases soil moisture storage (Ji and Unger, 2001). Crop residues at the soil surface shade the soil, serve as a vapor barrier against moisture losses from the soil, slow surface runoff and increase infiltration. Rathore et al. (1998) observed that more water was conserved in the soil profile during the early growth period with straw mulch than without it. Subsequent uptake of conserved soil moisture moderated plant water status, soil temperature and soil mechanical resistance, leading to better root growth and higher grain yields (Rathore et al., 1998).
SOC also helps in the amelioration of soil structure. However, this may be influenced by the type of SOC pool. For example recalcitrant C may produce long-lasting effects compared to the labile fraction (Jolivet et al., 2003, Rovira and Valejo, 2002). Soil aggregation, which is important to crop establishment, water infiltration and resistance to erosion and compaction, is also influenced by SOC content (Wright and Hons, 2005). Rapid changes in water-stable macroaggregation have been associated with variations in SOM (Cambardella and Elliot, 1993). For most soils macro-water-stable aggregates are stabilized by transient and relatively undecomposed organic binding agents (Tisdall and Oades, 1982). High correlation between aggregate stability and SOM has been reported by Chaney and Swift (1984) and others.
Mulching effects on soil bulk density are often variable. While some researchers have observed reduced soil bulk density under mulch (Unger and Jones, 1998), others have observed increased bulk density (Bottenberg et al., 1999) and yet others no mulch effect on bulk density (Blevin et al., 1983, Acosta et al., 1999, Duiker and Lal, 1999). The effects of mulching on bulk density may vary due to soil type, antecedent soil properties, type of mulch, climate and land use.
Although the beneficial effects of mulching are known, there are instances when its availability is limited. Crop residues have numerous competing uses (e.g. fodder, fuel and construction material). Similarly, costs are incurred in its application and these increase with mulch level. Therefore, it is necessary that an optimum mulch application rate be established if one is to enhance or maintain high soil quality in a cost-effective manner.
It is hypothesized that there is a threshold level of mulch beyond which the effect on soil properties is negligible. This critical level of mulch rate needs to be established for site-specific soil and environmental conditions.
The objectives of this study, therefore, were to:
- (1)
determine the optimum level of mulch application beyond which additional mulch results in minimal changes in soil properties, and;
- (2)
determine mulch level effects on soil bulk density, aggregation, soil moisture release characteristics and overall soil physical quality.
Section snippets
Location and treatment
The experiment was initiated in 1989, and sited at the Waterman Farm of The Ohio State University, Columbus, OH (40°00′N latitude and 83°01′W longitude). The experimental site has an annual average temperature of 11 °C and precipitation of 932 mm (USDA-SCS, 1980). The soil at the study site is classified as a Crosby silt loam soil (fine, mixed mesic Aeric Ochraqualf in the USDA Classification (USDA, 1996), and stagnic Luvisol in the FAO classification (FAO, 1988).
Wheat straw mulch was applied at
Soil moisture retention characteristics
Significant effects of mulch rate on soil volumetric moisture content were observed at low suction (Fig. 1). Moisture content at saturation varied and was the highest for 16 and 8 Mg/ha mulch rate and the least under unmulched treatment. The differences between treatments were more at low than at high suctions (Fig. 1). At 1500 kPa suction, there was no significant difference in moisture content among mulch rates (Fig. 1). The mulch effect on moisture retention diminished with an increase in the
Conclusions
The data presented supports the following conclusions:
Mulch application increased total porosity, AWC, soil aggregation and moisture content at field moisture capacity. However, mulch rate effect on soil bulk density was not linear.
Mulch rates as low as 2 Mg/ha resulted in dramatic increases in soil porosity compared to no mulch at all. Similarly, beyond 8 Mg/ha of mulch no significant increases in available water capacity were observed. At high suction, no treatment differences in soil moisture
References (39)
Advances in characterization of soil structure
Soil Till. Res.
(1988)- et al.
Crop residue and tillage effects on carbon sequestration in a Luvisol in central Ohio
Soil Till. Res.
(1999) - et al.
Modeling the effects of a partial residue mulch on runoff using a physically based approach
J. Hydrol.
(2003) - et al.
Short-term variations of soil physical properties as a function of the amount of C/N ratio of decomposing cotton residues. I. Soil aggregation and aggregate tensile strength
Soil Till. Res.
(1994) - et al.
Labile and recalcitrant pools of carbon and nitrogen in organic matter decomposing at different depths in soil: an acid hydrolysis approach
Geoderma
(2002) - et al.
Long-term tillage and cropping systems affect bulk density and penetration resistance of soil cropped to dryland wheat and grain sorghum
Soil Till. Res.
(1998) - et al.
The role of tree leaf mulch and nitrogen fertilizer on turfgrass soil quality
Biol. Fertil. Soils
(1999) - Blake, G.R., Hartage, K.H., 1986. Bulk density. In: Klute, A. (Ed.), Methods of Soil Analysis. Part 1. Physical and...
- et al.
Influence of conservation tillage on soil properties
J. Soil Water Conserv.
(1983) - et al.
Strip tillage reduces yield loss of snapbean planted in rye mulch
HorTechnology
(1999)