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1. Long-term nitrogen (N) addition plots on an upland Cal/una vulgaris moor had been treated for more than ten years with 0,40, 80 and 120 kg N ha-1 yr- 1 • 2. Sampling of the soil solution from under the mor and the mineral gley horizons over an annual cycle revealed a high degree of retention of N, between 60 % and 80 % of ambient N inputs in the control, and rising to 90 % in response to higher inputs of the N treatments. 3. After passing through the mineral gley horizon, N was further retained, by 85 % of ambient N inputs in the control, and rising to 97 % in response to the highest N treatment. 4. There was some evidence of an inverse relation between ammonium and dissolved organic nitrogen (DON) under all N treatments. Microbial immobilisation and conversion to DON was compatible with the few significant effects on cation concentration, although calcium and calcium/aluminium ratios and pH were decreased by N treatment in the mineral gley horizon. 5. A budget revealed that the added N of the treatments had been allocated mainly to the canopy and litter at low inputs and increasingly to the mor, and to a lesser extent the gley horizon, with increasing N inputs. 6. In the system as a whole, 51 % of the entire system N was contained in the mor horizon, and with increasing inputs of added N, the whole system N accounted for 60 %, 80 % and 90 % of the added N in the low, middle and high N treatments respectively. 7. Nitrogen/phosphorus ratios in green tissue were decreased in response to increasing N inputs to levels indicative of N limitation, in spite of increases in phosphatase activity in the litter and mor layers. N uptake rates and mycorrhizal colonisation were not affected. 8. A moor management bum volatilised 90 % of the canopy N (amounting to 6 % of the total system N). Increases in the gain ofN in the gley horizon after the bum decreased with increasing N treatment, an indication of increasing N saturation in this layer and confirmed by increases in N leaching in response to higher N inputs. The same response was observed without significance in the mor layer owing to greater variance in the data. 9. Rates of net mineralisation and DON production in the litter layer increased with N inputs in both field and laboratory incubations, but net nitrification rate only showed N treatment-related increases in the laboratory incubation. Threshold values of litter % N and C/N ratios determined the onset of these processes, as well as N treatment-related increases in rates of potential denitrification. 10. Bryophyte cover under the Calluna canopy, density of the canopy, light transmission through the canopy and N inputs were all related, either negatively or positively (see chapter 5), but only in mature/degenerate plants. In "new' plots containing younger, building-phase Calluna, the addition of phosphorus raised the competitive ability of bryophytes above that of Calluna, particularly at lower inputs of N.

Sugar beet <I>(Beta vulgaris. </I>L.) is sown to a stand in commercial agriculture. Consequently establishment of < 70 % can lead to an important loss in final yield and it is essential to obtain seed quality and pellet types that can give consistently high percentage emergence even under adverse soil conditions. This depends on suitable field testing and in use of vigour tests that can adequately simulate soil physical conditions in the field. In this study field and laboratory experiments were carried out to determine the effects of seed vigour, pellet type and soil physical conditions on the emergence of different sugar beet <I>(Beta vulgaris. </I>L.) seed lots. Field experiments were performed at three contrasting sites with seed lots of three different levels of vigour usually in four different types of pellet. The importance of imposing a stress was identified after the first field trial, in which few significant differences in percentage emergence were found. Therefore field trials with irrigated plots were carried out to determine the effects of heavy rainfall immediately after sowing. The result was a decrease in emergence percentage in irrigated plots and more significant differences (P <0.05) were found between seed lots. All field trials discriminated between high and low vigour seed (in common with laboratory tests) and between pelleted and unpelleted high vigour seed, but field tests did not rank order or discriminate as consistently between variants as did laboratory tests. Results from laboratory tests that were designed to simulate field conditions were compared with field emergence. Laboratory tests in soil or an artificial mixture (Erd and Sand-peat) under non-stressed conditions produced between 97.5-89.9 % emergence and did not differentiate well between different seed lots. In contrast 'wet' Erd and Sand-peat tests that had similar matric suctions to the irrigated field trials, gave between 90.1 to 50.4 % emergence, discriminated between different seed lots, correlated well with irrigated and other more stressed field trials. A model (BeetEM) predicting seedling emergence is also described and applied to sugar beet. The input variables are soil temperature at seed depth and the depth of sowing. The time for the hypocotyl to reach the soil surface is calculated using a base temperature and thermal time for hypocotyl appearance, and base temperature and thermal time and controlling the rate of pre-emergent shoot growth. Predicted emergence times were shorter than the observed. When the conditions were not stressed or seed lots were high in vigour the prediction was closer to the observed (within ½<I> - </I>1d out of a total of 12-14 d). However, in irrigated field trials low vigour seed lots took > 2 d longer to emerge than predicted.

Effects of fertigation at diverse water and fertiliser application rates on tomato (<i>lycopersicon esculentum</i>) yield and nutrient uptake efficiencies were studied. The treatment giving optimal water use efficiency reduced fruit yield by <i>ca.</i> 46% but, compared with that giving the greatest fruit yield, substantially reduced the fluxes of N and K leached to groundwater. The background salt concentrations in irrigation water and the fertiliser K facilitated ammonium mobilisation down in the soil profile. Fertilisation for maximum yield increased the fluxes of nutrients leached, and application of water to achieve optimal water use efficiency would be more sustainable. Tomato growth was evaluated also under different irrigation rates, but at constant rate of fertiliser application. A relatively low irrigation rate optimised water use efficiency and gave a yield that not significantly below that a higher irrigation rates. Fertiliser N use efficiency was improved at the N fertiliser application rate of only 70 kg ha^-1 used, more than eight times lower than that suggested from the previous experiment. This is a dramatic improvement in terms of the potential flux of N leached to groundwater. A simple drainage flow model was developed to show why lateral water movement helps explain the poor nutrient use efficiency observed in both experiments. Spatial variation in groundwater quality in a major crop-producing region of the U.A.E., was investigated. the distributions of major and trace chemical constituents of groundwater were assessed with reference to effects on drinking water quality compared with WHO standards. In particular, nitrate concentrations in groundwater were examined, to see if nitrate accumulation was a potential cause for concern in the U.A.E. In spite of the beneficial recharge from the Oman Mountain, there is a zone of saline ground water between 24° 20' and 24° 25' that may be attributed to more than 20 years of intensive use of the land for irrigated crop production. Drip irrigation leads to build up of salinity and nature just beyond the rooting volume. These zones are flushed by rare rainfall events that contribute to groundwater recharge.

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With the estimated increase in global demand for food and over-reliance on staple food crops, the exploitation of agricultural biodiversity is important to address food security challenges. The aim of this study is to develop approaches to transfer major informational and physical resources developed in model plant and major crop species to resources poor crop species, using oil palm and Bambara groundnut as two exemplar crops. XSpecies (cross-species) approach, the core approach of the study, is described as the approach which uses microarrays developed for a given species to analyse another related species. The use of the XSpecies approach (here the cross-hybridisation of DNA from oil palm onto heterologous Affymetrix microarrays for Arabidopsis and rice), is the first experiment reported in oil palm and focused on a bulked segregant analysis of different shell-thicknesses for oil palm fruit. Primers design involved screening candidate probe-pairs filtered using PIGEONS software against oil palm transcriptome sequences generated using 454 sequencing technology. The results provided an insight into the effects of sequence divergence between oil palm and the reference species (Arabidopsis and rice) onto the power of detecting single feature polymorphism (SFPs) in oil palm, implying the importance of close association between studied and model plant/crop in XSpecies approach. The XSpecies approach coupled with genetical genomics was also tested within legumes, with Bambara groundnut as the query species compared to soybean as the resource rich species (20 Mya). A mild drought experiment, conducted in a controlled environment glasshouse, used an F5 segregating population derived from a controlled cross between DipC and Tiga Nicuru in Bambara groundnut. The cross-hybridisation of Bambara groundnut leaf RNA to the soybean GeneChip individual oligonucleotide probes resulted in a total of 1,531 of good quality gene expression markers (GEMs) on the basis of the differences in the hybridisation signal strength. The first ‘expression-based’ genetic map (GEM map) was constructed using 165 GEMs spanning 920.3 cM of Bambara groundnut genome. The first high density DNA-marker genetic map of 1,341.3 cM combining dominant DArT and co-dominant SNPs, developed using the DArT Seq approach, with additional pre-existing microarray-based DArT and SSR markers, was also developed in the F3 segregating population. Both maps were combined to form the first integrated map of 1,250.7 cM with 212 markers. Morphological differences and the rapid reduction in stomatal conductance observed within the F5 segregating population in the drought experiment provided trait data for a QTL analysis. The comprehensive QTL analysis in Bambara groundnut detected significant QTLs for morphological traits using GEM map, including internode length, peduncle length, pod number per plant, pod weight per plant, seed number per plant, seed weight per plant, 100-seed weight, shoot dry weight and harvest index across four linkage groups: LG1, LG2B, LG8B and LG11A. The loci controlling internode length and peduncle length were also consistently mapped to single marker on LG1 in DArTseq map using F3 segregating population, suggesting that these two traits are probably controlled by single gene or two closely linked genes. Despite significant genotypes effects on stomatal conductance tested in ANOVA analysis, no major QTLs were detected, suggesting the contributions of a number of small genetic effects to stomatal conductance. A preliminary homology search using the LG1 linkage group markers and associated gene models showed the ability to develop a framework for identification of candidate genes in Bambara groundnut relative to soybean. The present study also developed the resources for an eQTL analysis in a cross-species context. Translation from major and model plant species to underutilised and resource poor crops is critical to be able to develop many crop species with potential for future agriculture. This study examines some of the approaches which might be adopted and replicated in various underutilised crop species.

Durum wheat (Triticum turgidum L. var durum) and spring barley (Hordeum vulgare L.) are the most widely grown crop species in the semi-arid to arid areas of the Mediterranean region. However, their average on-farm yields are relatively low, 1.95 and 2.60 t ha-1, respectively (FAO, 2007). Water is generally recognized as the most limiting factor for barley and durum wheat production in the Mediterranean, though it has been found, at least for some regions, that N fertilizer applications have been limiting (Passioura, 2002). Water in the Mediterranean is relatively scarce and predictions for 2025 show that water limitations for agricultural production in that region will intensify (IWMI, 2000). Nitrogen fertilizer represents a significant cost of production for the grower and may also have negative environmental impacts through nitrate leaching, use of fossil fuels for manufacture and application, and N2O emissions associated with denitrification. Reducing excessive N fertilizer inputs and increasing water productivity, whilst maintaining acceptable yields, will be aided by increases in uptake efficiency.

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No description available.

No description available.