Shepherd, Dr M. A. (2002) Understanding soil fertility in organically farmed systems (OF0164). ADAS Consulting Ltd.
This is the final report of the Defra project OF0164.
Organic farming aims to create an economically and environmentally sustainable agriculture, with the emphasis placed on self-sustaining biological systems rather than external inputs. Building soil fertility is central to this ethos. ‘Soil fertility’ can be considered as a measure of the soil’s ability to sustain satisfactory crop growth, both in the short- and longer-term. It is determined by a set of interactions between the soil’s physical environment, chemical environment and biological activity. The aim of this project was, therefore, to provide a better scientific understanding of soil fertility under organic farming.
The approach was to undertake a comprehensive literature review at the start of the project to assess and synthesise available information. Studies were then designed to address specific questions identified from the literature review.
The literature review was written during the first year of the project. In addition to submitting written copies to DEFRA, the chapters were posted on a project website: www.adas.co.uk/soilfertility.
The Review was based around key questions:
• What are the soil organic matter characteristics and the roles of different fractions of the soil organic matter?
• Do organically managed soils have higher levels of organic matter (SOM), with a resultant improvement in soil properties?
• Is the soil biology different in organically managed soils, in terms of size, biodiversity and activity?
• Do organically managed soils have a greater inherent capacity to supply plant nutrients?
• What are the nutrient pools and their sizes?
• What are the processes and rates of nutrient transfer in relation to nutrient demand?
• What are the environmental consequences of organic management?
The project also included a large amount of practical work. This necessarily covered a wide range of topics, which were examined in a series of separate studies:
• Soil microbiology: a series of measurements focusing on two sites, undertaken by University of Wales Bangor (UWB)
• Field campaigns in autumn 1999 and spring/summer 2000: separate field sampling campaigns focusing especially on nutrient pools, undertaken by HDRA, ADAS and IGER
• Incubation studies: a series of three separate experiments to look in more detail at N dynamics, managed by ADAS, with support from IGER and HDRA
From the literature review and the practical work, the following was concluded:
Organic matter is linked intrinsically to soil fertility, because it is important in maintaining good soil physical conditions (e.g. soil structure, aeration and water holding capacity), which contribute to soil fertility. Organic matter also contains most of the soil reserve of N and large proportions of other nutrients such as P and sulphur.
Field management data gathered from farmers showed, however, that organic matter returns are not necessarily larger in organic systems. Many non-organically farmed soils receive regular manure applications and the generally higher yielding crops on conventional farms may return larger crop residues. Conversely, many organic fields receive little or no manure, relying on the fertility building ley phase for organic matter input. This observation is important. Management practices within organic and non-organic systems are diverse, and all have consequences for soil fertility.
The Executive Summary at the start of the main attached report has additional sections on Soil Structure, Soil Biology, and Nutrient Cycling with some greater detail on comparisons of organic and conventional management and the consequences for soil fertility.
|Keywords:||soil fertility, rotations, nutrient cycles, soil structure, soil biology, knowledge transfer, nitrogen, phosphorus, potassium, OF0164|
|Subjects:|| Soil > Nutrient turnover|
Soil > Soil quality > Soil biology
Knowledge management > Education, extension and communication > Technology transfer
|Research affiliation:|| UK > Garden Organic (HDRA)|
UK > Institute of Grassland and Environmental Research (IGER)
UK > Other organizations
UK > ADAS
UK > Department for Environment, Food and Rural Affairs (DEFRA)
|Deposited By:||Defra, R&D Organic Programme|
|Deposited On:||13 Apr 2006|
|Last Modified:||12 Apr 2010 07:33|
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