The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 213

K.W.T. Gouldinget al. Role ofSOMand Manures in Sustainable Nutrient Cycling

4

The Role of Soil Organic Matter
and Manures in Sustainable
Nutrient Cycling

K.W.T. G OULDING , D.V. M URPHY , A. M ACDONALD ,
E.A. S TOCKDALE , J.L. G AUNT , L. B LAKE , G. A YAGA
AND P. B ROOKES

Soil Science Department,IACR-Rothamsted,Harpenden,
Hertfordshire AL5 2JQ, UK

Introduction

Soil organic matter (SOM) is vital to the sustainable use of soil because of
its role in maintaining soil structure, water-holding capacity, the microbial
biomass and soil fauna, and in nutrient cycling. The maintenance of SOM
through rotational ley-arable farming, and the effective utilization of
crop residues and manures, are central to organic farming, but there are
increasing indications that good SOM, manure and residue management
may also be important for conventional agriculture. For example, for many
years yields of wheat on the plots receiving optimum amounts of fertilizers
on the Broadbalk Experiment at Rothamsted were as good as, if not better
than, those produced with farmyard manure (FYM). Recently, however,
the largest yields (and, unfortunately, the largest losses to the environment)
have been obtained from the plot given FYM in autumn and extra nitrogen
(N) fertilizer in spring (Johnston, 1997). The reasons for this change are
not yet clear. The yield differences could be caused by a better supply of
nutrients from the manure, e.g. the slow, regular release of mineral N from
manure through the growing season better meets the N requirements of
the growing crop than the large, single, spring application of fertilizer N
currently used on Broadbalk. If so, this could be corrected relatively easily
by applying more appropriate types and amounts of fertilizers at the correct
times. Alternatively the difference could be due to more complex changes
such as improvements in soil structure, water-holding capacity and the root
environment caused by manure, or even to the impact of FYM on weeds
and below-ground pathogens.