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A series of experiments was conducted at three contrasting sites (Cambridge University Farm, Gleadthorpe and Terrington Experimental Husbandry Farms) in four years (1985-88) to examine the effect of site, season and husbandry on growth and water use of the potato variety Record. Crisp processing quality was assessed at harvest and after periods of storage. Confounding of site and season with husbandry was avoided by maintaining similar husbandry in one experiment common to all sites and seasons. In 1989 at Cambridge, crops were grown in polythene tunnels to determine the effect of controlled water input on the number of tubers and efficiency of water use. Growth, development and yield of crops with similar husbandry generally did not differ between sites and seasons. Effects of husbandry (e.g. date of planting and date of harvest) at each site in all years were generally large compared with site and season effects. However, physiological age of seed tubers and irrigation regime had very little effect. Intercepted radiation was converted to tuber dry matter with greater efficiency in 1987 at Gleadthorpe than at the other two sites. In 1987, there was no effect of site on water use (evapotranspiration) efficiency with respect to tuber dry matter production, but later plantings used water more efficiently than early plantings. In 1988, the early planting at Gleadthorpe used water more efficiently than a similar date of planting at Cambridge. Excluding rainfall and withholding irrigation increased water use efficiency in 1989, and yield was lower from a crop kept close to field capacity than one which received the same amount of water over the season, but at less frequent intervals. Restricting crop water availability to soil reserves reduced the number of tubers greater than 10mm, but irrigation regime had no consistent effect on the number of tubers initiated or retained where rainfall input could not be controlled. Water uptake was related to depth and density of rooting, and date of planting and irrigation regime had considerable effects on root distribution. There were interaction effects between site and season on crisp fry colour. Delayed harvest resulted in darker crisps, but fry colour after long-term storage (36-40 weeks) could not be predicted from the colour at harvest. No significant correlation could be established between individual, or total, tuber sugar concentration and crisp colour., Digitisation of this thesis was sponsored by Arcadia Fund, a charitable fund of Lisbet Rausing and Peter Baldwin.

Soil quality is intimately linked with soil biology. Recent research at Rothamsted Research (RRes) has shown that addition of Farm Yard Manure (FYM) can improve barley grain and straw yield within two years by more than 1t ha−1 each. Penetrometer measurements attribute this increase to an improvement in ease of root exploration in the soil, which, in turn, may be attributed to an increase in earthworm biomass and activity. These results suggest benefits from adding the right kind of organic matter can be achieved relatively rapidly in soils by feeding the soil organisms, which then bring about desirable changes in soil condition. We hypothesised crop yields will increase quickly (within four years) as a result of improved soil physical condition that results from feeding soil organisms, especially earthworms, with relatively small amounts of suitable organic matter additions. To test these ideas, we set up field experiments at Rothamsted Research farm (flinty clay loam soil) in Harpenden between 2012 to 2017. The four harvest years of the project allowed three field experiments to run. These covered two tillage regimes, four arable crop rotation combinations, five nitrogen treatments and fourteen organic matter recipes at a range of concentrations. Additionally, two outdoor pot experiments, growing winter wheat under a range of earthworm amendments, seven organic matter recipes and four soil types, were studied. The influence on soil physical properties, crop yields and earthworm populations were examined on selected plots and pots. Different methods were used on selected plots to examine soil physical properties. Methods included bulk density, infiltration, penetrometer, aggregate stability, resistance to ploughing or CT scans of the pores in soil. Earthworm populations were determined on selected plots by handsorting one 20 x 20 x 20cm cube taken from a plot. Microbial biomass, fungal biomass and microbial community composition were also measured. Five commercial growers’ trials were held at Haines Barn, Woodbridge, Butterwick, Terrington and Spalding (England). Data from three independent trials at AFBI (Northern Ireland), three at NIAB (England) and one at JHI (Scotland) were also included. These data included some yield data on cereal or horticulture cultivations, soil physical measurements and an earthworm survey. Crop yields were determined on every plot, with a beneficial yield effect detected on both the Rothamsted trials after two years of amendments. Amended soils in a pot experiment testing the effect of soil type had more tillers and greater grain masses than unamended soils but there was no significant difference between soil types. Yield improvement in a European study did increase with texture in the order clay

Wheat (Triticum aestivum L.) is the major UK arable crop with a total annual production of about 15 Mt. Intensive cultivation of wheat requires large inputs of fertiliser nitrogen (N), and of the total annual UK use of 1.1 Mt of N fertiliser, 0.36 Mt are applied to wheat crops. However, current cultivars are only able to take up a limited proportion of this applied N (50-60% in NW Europe; Bloom et al., 1998), and large amounts of N are lost to the environment. These fertilisers represent a cost to the grower, and have negative environmental impacts through nitrate, ammonia and greenhouse-gas emissions. There is therefore an increasing need to reduce fertiliser N inputs whilst maintaining or increasing yields. Developing new N-efficient genotypes is an important approach, and could be achieved by increasing the crop N-uptake efficiency (UPE; above-ground N uptake / N available) and/or the N-utilisation efficiency (UTE; grain DM yield / above-ground N uptake). Since only around 50% of the total canopy N is in the leaf lamina at anthesis, there may be scope to reduce the remainder, in particular the significant quantities of N contained in the true stem (up to 25% of canopy N). The overall aim of the present study was to investigate the physiological basis of yield responses to N supply in winter wheat and how cultivars differ in their responses, and to identify breeding targets for new cultivars with lower fertiliser requirements. Three field experiments were carried out: the first (sown October 2005) and third (sown October 2006) were ADAS Terrington, near King’s Lynn, UK, and the second (sown June 2006) was at the Institute for Crop and Food Research, Lincoln, New Zealand. At Terrington, six N fertiliser treatments were randomised on main plots and four cultivars of winter wheat (Istabraq, Atlanta, Claire, and Savannah) were randomized on sub-plots in a split-plot design with three replicates. The cultivars were chosen to contrast for N partitioning amongst plant organs at anthesis according to previous data sets. At Lincoln, six N fertiliser treatments were randomised on plots with six replicates for one cultivar (Istabraq). Plots were sampled at five developmental stages, with particular emphasis on anthesis and harvest. At each sampling, crop growth (above-ground N uptake, green canopy area, above-ground dry matter, and DM and N partitioning) was assessed, as well as fractional interception of photosynthetically active radiation (PAR). Data for N uptake and crop DM growth were related to the canopy N requirement (Sylvester-Bradley et al., 1990a) and critical N concentration (Justes et al., 1994) models for winter wheat, and the crop N status at anthesis was quantified according the N nutrition index (Lemaire et al., 1989). The crop N content at anthesis was allocated to three conceptual N pools: structural (SN), photosynthetic (PN) and reserve (RN); the reserve N pool was sub-divided into ‘storage’ (remobilised post-anthesis) and ‘accumulation’ N (not remobilised post-anthesis) pools (Staswick, 1994). Two N sourcesink manipulation treatments were imposed in the experiments approximately two weeks after flowering: defoliation (removal of leaf 3 and below on each shoot) and degraining (removal of all the spikelets from one side of the ear), to test responses of remobilisation of canopy N to changes in grain N source-sink balance. Results showed that NUE (grain dry matter yield / N available) decreased with N supply. Between the unfertilised and optimally fertilised N treatments the decrease was approximately equally associated with declining UPE and UTE. However, above the optimally fertilised N treatments only UPE continued to decline. The main driver of lower UTE was the biomass production efficiency (BPE; above-ground DM / aboveground N), and varietal differences in BPE at Terrington in 2006/7 indicated the potential to breed for superior UTE. The amount of fertiliser N required to maximise above-ground DM at anthesis was considerably less than that required to optimise yields at harvest (N opt-trt), and reserve N was observed to accumulate within the canopy at anthesis in all N treatments. This reserve N accounted for 41 and 44% of above-ground N (AGN) at the optimal and supra-optimal N rates, respectively. Reserve N was particularly located in the leaf lamina and true stem. The leaf lamina showed the highest PN content. However, the relationship between radiation-use efficiency (RUE; above-ground DM / PAR) during stem elongation and specific leaf N content (all culm leaves) at anthesis showed that the concentrations of N at the optimal and supra-optimal N treatments exceeded that required for effective photosynthesis, which was ca. 2 g N m-2, and indicated that the crop may be using these tissues as RN capacity, most likely in the photosynthetic enzyme ‘Rubisco’. Results showed that a large quantity of N is loaded in the true stem at anthesis (ca. 25% of AGN at the N opt-trt). The true stem had the highest SN content, but also contained considerable quantities of RN at all N treatments, particularly at the optimal and supra-optimal N treatments (averaged across experiments at 45 and 45 kg N ha-1, respectively; representing 42 and 38% of crop RN, respectively). The large physical capacity, central position and vascular role of the true stem makes this organ particularly suited to a RN function. Overall there was little genetic variation in N partitioning to the SN, PN and RN pools at anthesis (at the N opt-trt in the ranges 0.21-0.22, 0.42-0.44 and 0.35-0.37, respectively). This may have reflected the relatively narrow genetic basis of the germplasm used in this study (i.e. four elite UK cultivars with similar dates of release and end-use). Large quantities of N were remobilised post-anthesis (overall in the range 90-153 kg N ha-1 across the three experiments). Most N was from the leaf lamina - contributing 29- 35% to the grain N at harvest, with leaf sheath and true stem also providing 10-14% and 9-17%, respectively. This was relatively consistent across varieties. The N remobilised in the post-anthesis period (NR) appeared to be drawn mostly from RN pool in the first half of the grain-filling and then from PN pool in the second half of the phase. The timing and rate of canopy senescence was associated with canopy RN accumulation at anthesis, with senescence occurring predominantly after mid-grain filling in the well fertilised treatments when canopy RN capacity had declined. Senescence was also faster or slower where post-anthesis N remobilisation was increased or decreased in response to defoliation or degraining treatments, respectively. Present results showed that proportionally less true stem N at anthesis was remobilised during the grain filling period (i.e. lower N remobilisation efficiency; NRE) compared to the leaf lamina and leaf sheath, with little genetic variation observed in the Terrington experiments. Therefore the true stem contained considerable quantities of accumulation N at harvest at the optimal and supra-optimal N treatments (overall 12 and 17 kg N ha-1), and would appear to provide a realistic breeding target for reducing canopy N requirement. However, responses in the defoliation treatments demonstrated that true stem NRE could be significantly increased (overall by 20%) compared to the control, whilst the degraining treatments showed that grain N was mainly source limited, up to the upper limit of 1.1- 1.2 mg N grain-1 when it became sink limited. Overall observed genetic variation in UTE and underlying traits related to canopy N loading in the pre-anthesis phase and canopy N unloading in the post-anthesis phase was small in the present study. Nevertheless, several candidate traits were identified with potential to reduce fertiliser requirements in feed varieties. Firstly, increasing true stem RN capacity as means to increase the maximum rate of N uptake (kg N per day) during stem elongation may be feasible through optimisation of traits such as stem length and wall thickness. Secondly, modifying true stem RN unloading by increasing storage N in relation to accumulation N may offer a realistic mechanism for improving crop BPE and thus UTE. Such an increase in true stem NRE might be achieved through manipulation of key N assimilation enzymes. Thirdly, it may be possible to select for ‘stay-green’ traits associated with lower leaf lamina NRE and lower grain N% to boost UTE. However, in each case further phenotyping studies are required to characterise genetic variability, identify the most appropriate germplasm resources for genetic studies, and to identify appropriate genetic sources of variation for breeding.

Measurements were made of nitrate leaching, ammonia (NH3), nitrous oxide (N2O) and dinitrogen (N2) emissions, and crop offtake of N, together with wet N deposition in order to estimate annual fluxes of N inputs and N outputs at three sites, Gleadthorpe (GL), Terrington (TE) and Rosemaund (RO), in the UK over the three seasons 1995:96, 1996:97 and 1997:98. The soils were loamy sand, alluvial silt and silty clay loam, respectively. The objective of the project is to quantify all the major N fluxes over two arable rotations on contrasting soil types. Soil N at GL at 0.07‐0.08% was about half that measured at TE and RO (0.11‐0.17%). These differences were consistent with those usually found between soils of different clay content in an arable rotation. Over the first two winters excess winter rainfall (EWR) at all sites, especially TE, was less than average. In consequence amounts of nitrate-N leached were better related to EWR, than to the previous crop. Estimates of mineralization overwinter 1995:96 at 50‐60 kg:ha, did not differ consistently between sites or previous crops. Over the following winter data suggest net immobilization of soil mineral N (SMN). Using only measured fluxes, annual N2O losses of 0.5‐2.7% of fertilizer-N applied were estimated. Wet deposition of 20 kg N:ha at RO was greater than wet deposition at GL and TE of 7 kg N:ha. These differences were greater than expected from current national estimates of deposition. Wet deposition of N has contributed 5% of total N inputs and NH3 fluxes have usually been negligible. Outputs of N were dominated by crop offtake and nitrate leaching. Balances for winter wheat ranged from 85 to 57 kg:ha, largely in consequence of variation in N offtake, due to differences in yield and fate of straw, and also in nitrate leaching. Gaseous losses were usually small, and in total appear to be no greater than N inputs from wet deposition. Thus in arable systems where no organic manures are applied, priority in reducing losses of N to the environment needs to be given to nitrate leaching. © 2000 Elsevier Science B.V. All rights reserved.