A model was devised to describe simultaneously the grain masses of water and dry matter against thermal time during grain filling and maturation of winter wheat. The model accounted for a linear increase in water mass of duration anthesis—m1 (end of rapid water assimilation phase) and rate a, followed by a more stable water mass until m2, after which water mass declined rapidly at rate e. Grain dry matter was described as a linear increase of rate bgf until a maximum size (maxgf) was attained at m2. The model was fitted to plot data from weekly samples of grains taken from replicated field experiments investigating effects of grain position (apical or medial), fungicide (five contrasting treatments), sowing date (early or late), cultivar (Malacca or Shamrock) and season (2001/2002 and 2002/2003) on grain filling. The model accounted for between 83 and 99% of the variation (radj.2) when fitted to data from individual plots, and between 97 and 99% when fitted to treatment means. Endosperm cell number of grains from early-sown plots in the first season were also counted. Differences in maxgf between grain positions and also between cultivars were mostly the result of effects on bgf and were empirically associated with water mass at m1. Fungicide application controlled S. tritici and powdery mildew infection, delayed flag leaf senescence, increased water mass at m1 (wm1), and also increased m2, bgf and maxgf. Fungicide effects on water mass were detected before fungicide effects on dry matter, but comparison of the effects of individual fungicide treatments showed no evidence that effects on wm1, nor on endosperm cell numbers at about m1, were required for fungicide effects on maxgf.

The aim of this work was to investigate differences among genotypes in post-anthesis root growth and distribution of modern UK winter wheat cultivars, and the effects of fungicide applications. Post-anthesis root growth of up to six cultivars of winter wheat (Triticum aestivum L.), given either one or three applications of fungicide, was studied in field experiments during two seasons. Total root mass remained unchanged between GS63 (anthesis) and GS85, but root length increased significantly from 14.7 to 31.4 km m−2 in one season. Overall, there was no evidence for a decline in either root mass or length during grain filling. Root mass as a proportion of total plant mass was about 0.05 at GS85. There were significant differences among cultivars in root length and mass especially below 30 cm. Malacca had the smallest root length and Savannah the largest, and Shamrock had a significantly larger root system below 40 cm in both seasons. Fungicide applied at ear emergence had no significant effect on root mass in either season but increased root length (P<0.01) in the more disease-prone season. By maintaining a green canopy for longer, fungicide applied at flag leaf emergence may have resulted in delayed senescence of the root system and contributed to the post-anthesis maintenance of root mass and length.

Three field experiments, each repeated over two or three seasons, on winter wheat investigated a possible limit to the association between grain yield and flag leaf life, as extended by fungicide application. The experiments involved up to six cultivars and different application rates, timings and frequencies of the strobilurin azoxystrobin and the triazole epoxiconazole. In the 2000/01 and 2001/02 seasons, the relationships between the thermal time to 37% green flag leaf area (m) and yield deviated from linearity. ‘Broken stick’ models were fitted to cultivar × experiment combinations within each season and the limit to the benefit to yield associated with extending flag leaf life was 700 °C days (S.E. = 20.7) and 725 °C days (S.E. = 9.33) after anthesis in 2000/01 and 2001/02, respectively. In 2002/03, the relationship between yield and m did not deviate significantly (P > 0.05) from linearity, but in this latter year the fungicide application failed to increase m past 700 °C days.

Three successive field experiments (2000/01–2002/03) assessed the effect of wheat cultivar (Consort, Hereward and Shamrock) and fungicide (epoxiconazole and azoxystrobin) applied at and after flag leaf emergence on the nitrogen in the above-ground crop (Total N) and grain (Grain N), net nitrogen remobilization from non-grain tissues (Remobilized N), grain dry matter (Grain DM), and nitrogen utilization efficiency (NUtEg=Grain DM/Total N). Ordinary logistic curves were fitted to the accumulation of Grain N, Grain DM and Remobilized N against thermal time after anthesis and used to simultaneously derive fits for Total N and NUtEg.When disease was controlled, Consort achieved the greatest Grain DM, Total N, Grain N and NUtEg; in each case due mostly to longer durations, rather than quicker rates, of accumulation. Fungicide application increased final Grain DM, Grain N, Total N and Remobilized N, also mostly through effects on duration rather than rate of accumulation. Completely senesced leaf laminas retained less nitrogen when fungicide had been applied compared with leaf laminas previously infected severely with brown rust (Puccinia recondita) and Septoria tritici, or with just S. tritici. Late movement of nitrogen out of fungicide-treated laminas contributed to extended duration of both nitrogen remobilization and grain N filling, and meant that increases in NUtEg could occur without simultaneous reductions in grain N concentration.

3 1. Background and introduction 1.1. Root growth and distribution 4 1.2. Fungicide and nitrogen management 5 2. Materials and methods 2.1. Site details and general crop husbandry 8 2.2 Experimental design 2.2.1. Nitrogen x irrigation (NI) experiment 9 2.2.2. Fungicide experiments (F1 –F3) 9 2.3 Measurements 2.3.1. Nitrogen x irrigation (NI) experiment 11 2.3.2. Fungicide experiments (F1 –F3) 13 3. Results for nitrogen x irrigation (NI) experiment 3.1 Temporal development of the root and shoot 19 3.2 Effect of nitrogen on root and shoot growth 23 3.3 Effect of irrigation on root and shoot growth 25 3.4 Effects on grain yield and quality 29 4. Discussion of nitrogen x irrigation (NI) experiment 4.1 Temporal development of the root and shoot 30 4.2 Nitrogen fertilizer 30 4.3 Irrigation timing 31 4.4 Grain yield and quality 32 5. Results of fungicide (F1-F3) experiments 5.1. 2000/01 5.1.1. Experiment F1 5.1.1.1. Green leaf area and foliar disease 35 5.1.1.2. Nitrogen uptake and partitioning 35

Winter wheat was grown in three field experiments, each repeated over two or three seasons, to investigate effects of extending flag leaf life by fungicide application on the concentration, kgha−1 and mg grain−1 of nitrogen (N) and sulphur (S) as well as N:S ratio and sodium dodecyl sulphate (SDS) sedimentation volume. The experiments involved up to six cultivars and different application rates, timings and frequencies of azoxystrobin and epoxiconazole. For every day the duration to 37% green flag leaf area (m) was extended, N yield was increased by 2.58kgha−1, N per grain by 0.00957mg, S yield by 0.186kgha−1 and S per grain by 0.000718mg. The N:S ratio decreased by 0.0135 per day. There was no evidence that these responses varied with cultivar. In contrast, the relationship between flag leaf life and N or S concentration interacted with cultivar. The N and S concentrations of Shamrock, the cultivar that suffered most from brown rust (Puccinia recondita), increased with the extension of flag leaf life whereas the concentrations of N and S in Malacca, a cultivar more susceptible to Septoria tritici, decreased as flag leaf senescence was delayed. This was because the relationships between m and N and S yields were much better conserved over cultivars than those between m and thousand grain weight (TGW) and grain yield ha−1.

Two field experiments were carried out comparing a range of fungicide treatments. Medial and apical grains were repeatedly extracted from 10 ears per plot during grain maturation. Grain dry weight and moisture content were determined, modelled using a 'broken stick' method and parameters of the models compared. Fungicide increased final grain weight and duration of grain filling. In medial grains maximum water content during the linear phase of grain filling with dry matter was highly correlated with maximum grain weight (g dm), whereas, in apical grains maximum grain weight was correlated with water content at the end of grain filling with dry matter.