CROP GROWTH AND NITROGEN RECOVERY RESULTING FROM THE INJECTION OF SEWAGE SLUDGE
Report No FR0283

M J Hann, C J Atkinson and R J Godwin, Silsoe College

March 1992

SUMMARY

I OBJECTIVES

To study environmental and agronomic factors which influence the recovery and loss of nitrogen when sewage sludge is applied to arable land.

II REASONS

Current and future measures to protect ground and surface waters from nitrate emissions from agricultural land may constrain significantly sludge disposal practices. This will affect particularly those areas where sludge is applied largely in the autumn period to arable land in nitrate vulnerable zones.

III CONCLUSIONS

Soil injection of sludge increases yields of winter or spring wheat more than equivalent surface applications. The closer the application date is to sowing date then the grain yield and nitrogen recovery is greater. Injecting sludge into the crop post-emergence may be beneficial although this can cause mechanical damage, however, this tends to be less in winter wheat or in sandy soil compared with spring wheat or a clay soil. Improved crop recovery of nitrogen implies reduced loss from the soil.

IV RESUME

This interim report presents the agronomic results of a series of field trials conducted at Silsoe College. In these trials, liquid digested sludge was injected and surface applied to arable plots at intervals over the autumn, winter and spring period, and were either sown with winter wheat or left uncropped until sowing with spring wheat. Applications were also made post-emergence.

The trials were conducted on both sandy and clay soils. The crops were monitored for yield and nitrogen content, and effects are discussed in relation to nitrogen additions, method and timing of applications, climatic factors, soil type, and time of sowing. A lysimeter trial was also carried out with some of the principal treatments and the amounts of nitrate leached were measured. All the field trials were regularly soil sampled and analysed for nitrate content, the results of which will be presented and discussed in relation to these agronomic aspects in a separate report.

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