Nitrogen for spring-sown malting barley

Field experiments were carried out to determine the effect of nitrogen on the yield, nitrogen uptake and grain nitrogen concentration of spring barley grown for malting. The effects of the rate, timing of application and the form in which the fertiliser nitrogen was applied were studied. The form of fertiliser nitrogen applied had little effect on grain nitrogen concentrations, except under dry soil conditions, when concentrations were higher using calcium nitrate fertiliser. Calcium nitrate also improved grain yields at low fertiliser rates, but at rates nearer recommended levels there was little difference in yield between fertiliser forms. Split or late applications of fertiliser nitrogen only improved yields when applied as calcium nitrate, and then only when early applications had been followed by heavy rain. At low fertiliser rates, the efficiency of recovery of fertiliser nitrogen (l^N ) in plant shoots was greater, when applied as calcium nitrate than when applied as ammonium sulphate or ammonium nitrate. Efficiency of recovery fell at higher rates in calcium nitrate treatments, but rose in ammonium sulphate treatments. Under the dry soil conditions in 1989, the efficiency of recovery was significantly increased in all fertiliser treatments. Uptake of fertiliser nitrogen was rapid in the calcium nitrate and ammonium nitrate treatments, usually reaching a maximum by anthesis. There was evidence of losses, between anthesis and harvest, of fertiliser nitrogen previously taken up by the crop. The uptake of soil nitrogen in the calcium nitrate treatments remained constant over the range of rates and timings of fertiliser application. There was evidence of increasing uptake of soil nitrogen with increased rates of ammonium sulphate fertiliser at several sites, possibly due to ’pool substitution’ of 15N_iabelled fertiliser. Uptake of soil nitrogen was less rapid than fertiliser nitrogen before anthesis, but continued right up to harvest in most treatments. This appeared related to calculated rates of gross mineralisation, which increased during the growing season. The most significant factor in determining total nitrogen uptake in the crop was the soil on which the barley was grown, rather than any of the fertiliser management treatments studied. Soil nitrogen uptake was significantly more variable between sites than fertiliser nitrogen uptake, despite the similar cropping histories at most sites. The variation in soil nitrogen uptake was derived mainly from differences in the mineralisation of soil organic m atter over the growing season, rather than from the amount of mineral nitrogen in the soil at sowing. Good correlations were found on all ADAS N-Index zero soils, between soil nitrogen taken up in the plant and values obtained using potassium chloride extraction techniques for measuring potentially mineralisable nitrogen. Further work is required to validate this relationship over a wider range of soils, and also to determine whether the relationship will hold for earlier sampling, which would be necessary if the technique was to become widely used. CONTENTS Page ACKNOWLEDGEMENTS i ABSTRACT ü CONTENTS iv 1: INTRODUCTION 1 2: LITERATURE REVIEW 3 2.1: Malting Barley 3 2.1. 1: Importance of spring barley in Scotland 3 2.1. 2: Production of malt 5 2.1. 2.1: The malting process 5 2.1. 2.2: Quality requirements for malting 5 2.2: Barley Growth and Yield 6 2.2.1: Environmental factors 6 2.2.2: Effect of nitrogen on yield and quality 8 2.3: Nitrogen Uptake 9 2.3.1: Introduction 9 2.3.2: Fertiliser and soil nitrogen 9 2.3.2.1: Plant uptake o f fertiliser nitrogen 9 2.3.2.2: Plant uptake o f soil nitrogen 11 2.3.2.3: The priming effect and the interpretation o f 11 experiments 2.3. 3: Influence of fertiliser management 14 2.3. 3.1: Ammonium versus nitrate nutrition 14 2.3. 3.2: Timing o f application 16 2.4: Nitrogen Transformations in the Soil 17 2.4. 1: Integration of soil nitrogen subcycles within the 17 universal nitrogen cycle 2.4. 2: Minéralisation-immobilisation turnover (MIT) 19 2.4. 3: Effect of environmental conditions 21 2.4. 4: Nitrification 22 2.5: Prediction of the Fertiliser Nitrogen Requirement 23 2.5. 1: Fertiliser recommendation systems 23 2.5. 2: Assessment of soil nitrogen supply 24 2.5. 2.1: Residual mineral nitrogen 24 2.5. 2.2: Previous cropping 25 2.5. 2.3: Estimation o f potentially mineralisable nitrogen 26 2.5. 2.4: Computer modelling o f fertiliser nitrogen requirement 31 2.5. 2.5: Direct measurement o f mineralisable nitrogen 32 3: SITES, MATERIALS AND METHODS 35 3.1: 1987-1989 Seasons 35 3.1. 1: Site preparation and fertiliser application 35 3.1. 2: Plant sampling, preparation and analysis 38