A review of leguminous fertility-building crops, with particular reference to nitrogen fixation and utilisation

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Cuttle, Shepherd & Goodlass, 2003

Text of A review of leguminous fertility-building crops, with particular reference to nitrogen fixation and...

  • A review of leguminous fertility-building crops, withparticular refence to nitrogen fixation and utilisation

    Written as a part of Defra Project OF0316The development of improved guidance on the use of fertility-building

    crops in organic farming

    Authors:

    Dr Steve Cuttle Institute of Grassland & Environmental Research,Plas Gogerddan, Aberystwyth SY23 3EB

    Dr Mark Shepherd ADAS Gleadthorpe Research Centre, Mansfield,Notts NG20 9PF

    Dr Gillian Goodlass ADAS High Mowthorpe Research Centre,Duggleby, Malton, N. Yorks, YO17 8BP

    October 2003

  • CONTENTSEXECUTIVE SUMMARY................................................................................................................................. 1

    1. INTRODUCTION................................................................................................................................... 14

    1.1. WHAT ARE FERTILITY-BUILDING CROPS?............................................................................................ 141.2. ROLE IN ROTATIONS .............................................................................................................................. 141.3. WHAT IS FERTILITY?........................................................................................................................... 151.4. NUTRIENT SUPPLY ................................................................................................................................. 161.5. ORGANIC MATTER ................................................................................................................................. 181.6. OBJECTIVES OF REVIEW......................................................................................................................... 191.7. DEFINITION OF TERMS ........................................................................................................................... 191.8. KEY ISSUES............................................................................................................................................ 20

    2. FERTILITY-BUILDING CROPS IN ROTATIONS........................................................................... 21

    2.1. INTRODUCTION...................................................................................................................................... 212.2. DISEASE IMPLICATIONS OF FERTILITY-BUILDING CROPS ........................................................................ 282.3. THE INTERACTION OF FERTILITY-BUILDING CROPS AND INVERTEBRATE PESTS...................................... 312.4. INTERACTIONS BETWEEN PESTS AND DISEASES ..................................................................................... 402.5. CONCLUSIONS ....................................................................................................................................... 44

    3. HOW MUCH N IS CAPTURED? ......................................................................................................... 45

    3.1. FIXATION POTENTIAL OF DIFFERENT CROPS........................................................................................... 453.2. FACTORS AFFECTING N ACCUMULATION............................................................................................... 693.3. CONCLUSIONS ....................................................................................................................................... 90

    4. THE INFLUENCE OF MANAGEMENT............................................................................................. 92

    4.1. EFFECTS OF CUTTING AND MULCHING ON N CAPTURE AND LOSS .......................................................... 924.2. EFFECTS OF FORAGE OR GRAIN HARVEST ON N CAPTURE AND LOSS...................................................... 954.3. EFFECTS OF GRAZING ON N CAPTURE AND LOSS.................................................................................... 984.4. INTERACTIONS WITH MANURES AND COMPOSTS .................................................................................. 1014.5. EFFECTS OF SOIL MANAGEMENT AND CROP ROTATIONS ...................................................................... 1024.6. CONCLUSIONS ..................................................................................................................................... 103

    5. USE OF MODELS TO ESTIMATE N-FIXATION........................................................................... 105

    5.1. SIMPLE YIELD-BASED MODELS ............................................................................................................ 1055.2. MORE COMPLEX MODELS .................................................................................................................... 1065.3. CONCLUSIONS ..................................................................................................................................... 109

    6. UTILISING N FROM FERTILITY-BUILDING CROPS ................................................................ 110

    6.1. INTRODUCTION.................................................................................................................................... 1106.2. FACTORS AFFECTING N MINERALISATION ........................................................................................... 1116.3. NITROGEN LOSSES ............................................................................................................................... 1136.4. INTERACTIONS WITH CROP UPTAKE ..................................................................................................... 1186.5. PREDICTING N RELEASE ...................................................................................................................... 1206.6. CONCLUSIONS ..................................................................................................................................... 122

    7. ROTATIONAL ASPECTS................................................................................................................... 123

    7.1. FARM PRACTICES................................................................................................................................. 1237.2. NUTRIENT BALANCES .......................................................................................................................... 1257.3. CONSTRUCTING ROTATIONS ................................................................................................................ 1287.4. COMPANION CROPPING (BI-CROPPING) ............................................................................................. 1297.5. CONCLUSIONS ..................................................................................................................................... 130

    8. CONCLUSIONS.................................................................................................................................... 131

    8.1. HOW MUCH N IS FIXED UNDER UK CONDITIONS? ............................................................................... 1318.2. MANAGEMENT TO OPTIMISE N ACCUMULATION.................................................................................. 1328.3. RATE OF RELEASE OF FIXED N AND MINIMISING LOSSES...................................................................... 1338.4. OTHER CONSIDERATIONS .................................................................................................................... 134

    9. BIBLIOGRAPHY ................................................................................................................................. 139

  • A review of leguminous fertility-building crops, Defra project OF0316 Executive Summary

    Written by S Cuttle, M Shepherd & G Goodlass Page 1

    EXECUTIVE SUMMARY

    The cornerstone of the organic philosophy is the use of legume based leys to build fertility.Indeed, the organic standards require the inclusion of legumes in the rotation. Fertility-building crops and green manures are therefore key components of organic rotations. Theregulations contain no specific requirements for ley management and the paucity of researchmeans that their management is often based on hearsay rather than empirical evidence.Management options for these crops are many, including: choice of species and cultivar; length of growing period within the rotation; rotational position and management of foliage (cutting and exporting, cutting and

    mulching, grazing or combinations of these).

    These factors will affect the amount of N fixed during the fertility-building stage, i.e.influence the amount of N that has been captured. Efficient use of the captured N by thefollowing crops relies on management practices and cropping patterns that make best use ofthe N released by mineralisation of the residues

    The logical starting point is a synthesis of the current state of knowledge. The objective ofthis review is therefore to review effects of soil fertility-building crops on: N capture N use Pest, disease and other effects Available models for predicting N captureThe use of leguminous fertility-building crops represents an import of N into the system viafixation of atmospheric N. It is the most important source of N in the rotation. Therefore,the focus of this review is in managing N: fixation and the factors that affect it, andsubsequent mineralisation and use of the fixed N by arable crops. However, the use offertility-building crops should also be valuable in the conservation of other nutrients besidesN, particularly K and Ca (both more mobile in soil than P). Such crops should also benefitsoil structure since optimal aggregate stability requires the frequent turnover of youngorganic matter residues. There are indications that clover has additional benefits on soilstructure.