Organic carbon additions: effects on soil bio‐physical and physico‐chemical properties

Abstract

The effects of organic carbon (OC) additions from farm manures and crop residues on selected soil biophysical and physico-chemical properties were measured at seven experimental sites, on contrasting soil types, with a history of repeated applications of farm manure or differential rates of inorganic fertilizer nitrogen (N). Repeated (> 7 years annual additions) and relatively large OC inputs (up to 65 t OC ha À1 ) were needed to produce measurable changes in soil properties, particularly physical properties. However, over all the study sites, there was a positive relationship between OC inputs and changes in total soil OC and 'light' fraction OC (LFOC), with LFOC providing a more sensitive indicator of changes in soil organic matter status. Total soil OC increased by an average of 3% for every 10 t ha À1 manure OC applied, whereas LFOC increased by c. 14%. The measured soil OC increases were equivalent to c. 23% of the manure OC applied (up to 65 t OC ha À1 applied over 9 years) and c. 22% of the crop residue OC applied (up to 32 t OC ha À1 over 23 years). The manure OC inputs (but not crop residue OC inputs) increased topsoil porosity and plant available water capacity, and decreased bulk density by 0.6%, 2.5% and 0.5% with every 10 t ha À1 manure OC applied, respectively. Both OC sources increased the size of the microbial biomass (11% increase in biomass C with 10 t OC ha À1 input), but only manure OC increased its activity (16% increase in the soil respiration rate with 10 t OC ha À1 input). Likewise, the potentially mineralizable N pool only increased with manure N inputs (14% increase with 1 t manure total N ha À1 ). However, these soil quality benefits need to be balanced with any potential environmental impacts, such as excessive nutrient accumulation, increased nitrate leaching and phosphorus losses and gaseous emissions to the atmosphere.

Modification of sandy soil hydrophysical environment through bagasse additive under laboratory experiment

“…Total soil porosity was calculated assuming particle density 2.65 g cm -3 using the following equation (Bhogal et al, 2009): Total soil porosity = [1-(bulk density/2.65)] 100%. (1) The aggregate size distribution of each treatment was determined using the same core samples that were used to calculate the bulk density.…”

Improvements in the Quality of Agricultural Soils Following Organic Material Additions Depend on Both the Quantity and Quality of the Materials Applied

“…For example, changes in the total SOC pool have been shown to depend on the amount of organic material (C) applied, but not on the type of material (e.g., Rasmussen et al, 1980) whereas there is conflicting evidence on the response of other soil properties to the type of material applied. For example, Bhogal et al (2009) observed that repeated OC inputs (for at least 7 years) in the form of livestock manures led to improvements in soil physical properties (bulk density, porosity, and available water capacity) whereas OC additions in the form of crop residues (straw) did not. By contrast, Peltre et al (2015) measured changes in specific draft force that were related to the amount of OC applied and its effect on bulk density rather than due to differences in the type of organic material (including compost, livestock manures and sewage sludge applied annually over 11 years).…”

“…The application of organic materials to agricultural soils is a widely recommended practice not only as a source of essential plant nutrients which can provide savings in inorganic fertilizer use (Defra, 2010), but also as a means of increasing soil organic carbon (SOC) levels with associated improvements in soil biological and physical functioning (Bhogal et al, 2009). Indeed, the benefit of a range of organic material applications (livestock manures, composts, biosolids, etc.,) for SOC and soil quality has been widely documented and reviewed (e.g., Edmeades, 2003;Johnston et al, 2009).…”

Stability of Soil Organic Matter and Soil Loss Dynamics under Short-term Soil Moisture Change Regimes

“…If the C/N ratio of residue >24, available soil N is consumed by microbes and this retards decomposition rate. A number of authors have reported linear increases in SOC related to the amount of organic matter applied, whilst others, have reported that the rate of SOC accumulation is dependent on the source of organic carbon [14][15][16]. This greatly suggests the lowest (15 mm) average rainfall received in June and the highest (108 mm) in January.…”