Soil and organic matter processes

Lead Research Organisation: Rothamsted Research
Department Name: Unlisted


The focus of this project is on organic matter and biological residue interaction in grassland soils. It consists of two components:

1. Biochemical and physical characterisation of organic matter, including the use of NIRS for analysing complexity of biological organic matter. This work is linked to the SoilCIP (Objective 1)
2. Novel process studies to examine infiltration of viscous liquids. This research will test the hypothesis that infiltration rates of livestock slurries control key soil processes influencing nutrient release, gaseous emissions and diffuse pollution to water.

This project is influenced by and provides information for another North Wyke project (project number 5740) in the 'Grassland, environment and soil systems' Strategic Programme Grant area.


10 25 50
Description In this project we addressed the overall hypothesis that the physico-chemical characteristics of livestock derived organic matter (LD-OM) effects the fate of carbon and nitrogen in applied LDOM as a function of how it influences its physical position within the soil profile, accessibility by micro-organisms and substrate quality.

Stable isotopes of carbon and nitrogen, either enriched or at natural abundance, are an effective tool in the quantifying of rates of mineralisation of amended organic matter fractions and residual soil organic matter. Other naturally occurring tracers within livestock manure offer a useful method of tracing the transfer of organic amendments through the soil and landscape. New analytical techniques, including stable isotope tracing, are providing new quantitative information about the relationships between the N, P and C macronutrient cycles in agroecosystems, and have the potential to enable sustainable nutrient management at the whole farm scale.

In the absence of macro-pores, soil acts in a similar way to a chromatographic column, separating out the coarser slurry fractions at or in the soil surface, with finer fractions and the liquid fraction having greater potential to be transported to greater depth within the soil profile. The fractionation of livestock slurries into components, e.g. operationally defined size classes (similar to those for soil particles), or pools with pre-determined different N release patterns provides an improved approach to assessing the fate of applied livestock derived organic matter (LDOM) to soil.

Research confirmed that substrate quality of organic matter amendments influences short- and long-term gross and net mineralisation rates of carbon and nitrogen, and that organic matter accessibility to micro-organisms is key to turnover rates. We found that substrate quality (C:N) of LDOM particles is a function of particle size, with smaller particle sizes having higher C:N ratio and a large surface area: volume ratio, resulting in greater mineralisation rates than coarser particles. Different sized particle fractions of cattle slurry resulted in both positive and negative priming of soil carbon and that higher amounts of carbon are released from finer slurry particle sizes in the short- (days - months) and medium-term (months-years).

Position of LDOM within the landscape and within the soil profile is controlled by the density, shape and mass of the LDOM constituent parts, as well as hydrological energy; and it's position in the soil (and landscape) influences the proximate environmental conditions and hence microbial activity. Mineralisation rates are generally greater in the upper soil layers where conditions are more aerobic, whilst LDOM that is transported to depth will encounter anaerobic conditions more favourable for processes such as denitrification, and nitrous oxide production.
Exploitation Route Our research has shown that carbon additions to soil in amendments offer the opportunity for sequestration. This offers the opportunity for offsetting GHG emissions. also the prediction of rates of C and nutrient release means that the fertiliser replacement rate of e.g. livestock manures, can be utilised more effectively.
Sectors Agriculture, Food and Drink,Environment

Description The findings have featured in farmer discussion groups re: organic matter building in soil, climate change mitigation and nutrient use efficiencies from manures
First Year Of Impact 2010
Sector Agriculture, Food and Drink,Environment
Impact Types Economic,Policy & public services