https://pubag.nal.usda.gov/download/26859/pdf

Pedotransfer functions: bridging the gap between available basic soil data and missing soil hydraulic characteristics

The impact of heavy traffic on forest soils: A review

Soil is a potential C sink and could offset rising atmospheric CO 2 . The capacity of soils to store and sequester C will depend on the rate of C inputs from plant productivity relative to C exports controlled by microbial decomposition. Management practices, such as no-tillage and high intensity cropping sequences, have the potential to enhance C and N sequestration in agricultural soils. An investigation was carried out to study the influence of long-term applications of fertilizers and manures on different organic C fractions in a Typic Haplustept under intensive sequence of cropping with maize–wheat–cowpea in a semi-arid sub-tropic of India. In 0–15 cm, the bulk density was lowest (1.52 Mg m −3 ) in plots treated with 100% NPK + FYM, while the control treatment showed the highest value (1.67 Mg m −3 ). Balanced application of NPK (100% NPK) showed significantly lower bulk density (1.56 Mg m −3 ) over either 100% N (1.67 Mg m −3 ) or 100% NP (1.61 Mg m −3 ) in surface soils. The application of super-optimal dose of NPK (150% NPK) showed higher total organic C (TOC) (12.9 g C kg −1 ) over either 50% NPK (9.3 g C kg −1 ) or 100% NPK (10.0 g C kg −1 ) in 0–15 cm soil layer. There was an improvement in TOC in 100% NPK or 100% NP (9.3 g C kg −1 ) over 100% N (8.7 g C kg −1 ) in the same depth. The application of FYM with 100% NPK showed 15.2, 9.9 and 5.2 g C kg −1 in 0–15, 15–30 and 30–45 cm, respectively. Application of graded doses of NPK from 50 to 150% of recommendation NPK significantly enhanced other organic C fractions like, microbial biomass C (MBC), particulate organic C (POC) and KMnO 4 oxidizable C (KMnO 4 –C) in all the three soil depths. The TOC in 0–45 cm soil depth in 150% NPK (63.5 Mg C ha −1 ) was increased by 39% over that in 50% NPK treatment (51.5 Mg C ha −1 ) and 29% over that in 100% NPK treatment (54.1 Mg C ha −1 ). Integrated use of farmyard manure with 100% NPK (100% NPK + FYM) emerged as the most efficient management system in accumulating largest amount of organic C (72.1 Mg C ha −1 ) in soil. Nevertheless, this treatment also sequestered highest amount of organic C (731 kg C ha −1  year −1 ). Particulate organic carbon, a physically protected carbon pool in soil, could well be protected in sub-surface soil layers than in surface soil layer as a means of carbon aggradations. Microbial metabolic quotient (qCO 2 ) was significantly lower in 100% NPK + FYM over other treatments to indicate this to be the most efficient manuring practice to preserve organic carbon in soil where it facilitates aggradations of more recalcitrant organic C in soil. As compared to POC, total TOC proved to be a better predictor of MBC as it strongly correlated with total carbon mineralized from soil.

Long-term manuring and fertilization effects on soil organic carbon pools in a Typic Haplustept of semi-arid sub-tropical India

No-tillage and soil physical environment

A soil aggregate is “a group of primary soil particles that cohere to each other more strongly than to other surrounding particles” (Soil Science Society of America, 1997). Soil aggregates can be formed by both aggregation and fragmentation processes. There are several ways of quantifying aggregate size and cohesive strength. The relative abundance of aggregates at each possible size, after breaking the soil into individual aggregates in a prescribed way, is the usual representation of the characteristic size distribution. Similarly, an abundance index may indicate stability, as the fraction of soil material that remains aggregated after a specified disruptive procedure. Other stability indices relate more directly to the force required to break an aggregate apart, usually in terms of the mechanical energy per soil mass that must be applied to achieve a certain result, such as aggregate rupture. The analysis of soil aggregation is important in a variety of applications. Aggregate stability and size information may be used to evaluate or predict the effects of various agricultural techniques, such as tillage and organic-matter additions, and erosion by wind and water. Aggregate analysis is often used in experiments where various tillage methods are applied and then evaluated by examining the resulting stable aggregates. Because of their direct relation to cohesive forces, aggregate size and stability are important to understanding soil erosion and surface sealing. Analysis of dry aggregates may be used to estimate possible wind-erosion effects, while wet analysis may be more appropriate to evaluate or predict erosion due to rainfall impact and runoff. The stability of wet aggregates can be related to surface-seal development and field infiltration, as water-stable fractions may restrict water entry and form surface seals (Loch, 1994). Through these erosion and sealing effects, as well as the relation between aggregation and structural features such as macropores, aggregate analysis may help us understand most aspects of soil water behavior, including runoff, infiltration, and redistribution, as well as soil aeration and root growth. Increasingly, aggregate properties are being used in models that predict soil hydraulic properties, including water retention and unsaturated hydraulic conductivity (e.g., Rieu & Sposito, 1991a, b; Nimmo, 1997; Kosugi & Hopmans, 1998). The strength of interparticle cohesion depends on a variety of soil physical, chemical, and biological influences, some of the most important being air–water

2.6 Aggregate Stability and Size Distribution

Particle-size distribution in soils: A critical study of the fractal model validation

Soil compaction is recognized as an increasingly challenging problem for the agricultural, horticultural and forest production in many climatic regions. The Proctor test provides a standardized method to study compactibility of disturbed soils over a range of soil water contents. The objectives of our study were: (a) to determine values of the critical water content for compaction and maximum bulk density from Proctor compaction curves for soils different in their properties; (b) to study the correlation between the maximum bulk density and readily available soil properties. Thirty soil samples were taken from six different locations in Argentina between 58 and 64°W and 34 and 38°S. The degree of saturation at maximum bulk density varied from 73.2 to 96.8%. Comparison of our data with data of two studies in USA showed that relationships between the maximum bulk density and the critical water content were similar to these studies. However, the slope of the relationship between the maximum bulk density and the organic carbon content was 50% less in our study as compared with the two others. The maximum bulk density was highly correlated with the organic carbon content and the silt content, the determination coefficient of the multiple linear regression, r2, was 0.88.

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Maximum compactibility of Argentine soils from the Proctor test;: The relationship with organic carbon and water content

Saturated Hydraulic Conductivity (Ks) is an important parameter for agriculture. Some authors have studied Ks anisotropy in soils with different results. Several methods have been developed and modified with time for the determination of Ks. The aim of this study was to determine Ks anisotropy of a typic Argiudoll under conservation (T2) and no-till (T1) treatments by laboratory measurements on samples extracted in vertical and horizontal directions and to compare them with those obtained from field measurements with a tension disc infiltrometer. In order to determine Ks anisotropy undisturbed samples were collected at different depths (0–15 cm and 15–30 cm) and orientation (vertical and horizontal). Ks was also determined from field infiltration tests. Additionally bulk density ( ρ b ) was determined by gravimetric methods. Ks was anisotropic at 0–15 cm in both treatments (horizontal Ks was about five times larger than vertical Ks in both treatments), and isotropic at 15–30 cm. Ks determined from field infiltration tests did not differ from vertical Ks for all treatment-depth combinations. To summarize, mean values of Ks varied between 0.51 and 9.48 cm h −1 . Mean values of bulk density ( ρ b ) ranged from 0.98 (T2, surface) to 1.23 (T2, subsurface). The ρ b values were significantly greater at subsurface for both tillage systems. At this depth ρ b was significantly greater for T2. Water entry into the soil profile was conditioned by vertical Ks values. The values obtained from field measurements with a tension disc infiltrometer were similar to vertical Ks measured in laboratory in all cases.

Anisotropy of Saturated Hydraulic Conductivity in a soil under conservation and no-till treatments.

Relating soil structure to soil hydraulic properties is an important issue for understanding and managing soil functioning. Fractal models were applied to relate soil water retention and soil structure. One such model developed by Rieu and Sposito (1991a) predicts an equality of (i) soil matrix fractal dimensions derived from 'aggregate bulk density- aggregate size data' and (ii) soil fractal dimensions derived from water retention. The objective of this work was to test the statistical hypothesis of such equality for model soil systems of packed soil aggregates. Typic Argiudol and Typic Argiaquol soils were sampled at eight locations that differed in long-term management practices. Soil water retention was measured at 12 levels of soil matric potential ranging from -1200 to -20 kPa. The 'aggregate bulk density-aggregate size' data were obtained for seven ranges of aggregate sizes from 0.25 to 16 mm. The statistical hypothesis about the equality of mass fractal dimension as derived from the aggregate bulk density data and the scaling dimension of water retention could not be rejected in our study.

Roberto R. Filgueira

Papers

Particle-size distribution in soils: A critical study of the fractal model validation

Maximum compactibility of Argentine soils from the Proctor test;: The relationship with organic carbon and water content

Anisotropy of Saturated Hydraulic Conductivity in a soil under conservation and no-till treatments.

Comparison of Fractal Dimensions Estimated from Aggregate Mass-Size Distribution and Water Retention Scaling

The microwave spectrum of pyrrolidine