Increasing demand for timber, fuelwood and other forest products has outstripped production in many areas of the semi-arid tropics, leading to deforestation and land degradation resulting from erosion and nutrient depletion. Agroforestry offers the potential to provide forest products, improve productivity and reduce soil erosion and environmental degradation. However, as previous reports have shown that competition between trees and crops for water in semi-arid areas adversely affects crop yields, attention has turned towards studies of the existing practice of boundary planting, where low tree planting densities and the associated benefits of land demarcation and soil stabilisation increase the viability of incorporating trees into crop land. The aim is to select and manage tree species in ways that limit their negative effect on crop yields and improve the overall value of the system. The present study was carried out at Machakos (1° 33' S, 37° 14' E, altitude 1660 m) in the Kenyan highlands, where the bi-modal annual rainfall of c. 740 mm is divided approximately equally between two rainy seasons (short rains, October-February, long rains, March July). The experiment was set up in April 1993 to examine the influence of tree/crop interactions on system productivity. Each 18 x 18 m plot, except for the sole crop plots, contained a central row of trees planted at 1 m spacing. Four overstorey agroforestry treatments were examined between March 1996 and March 1998; these included two indigenous species, Croton megalocarpus and Melia volkensii, and two exotic species from Central America, Senna spectabilis and Gliricidia sepium. Beans (Phaseolusulgaris) and maize (Zea mays) were grown during the short and long rains respectively. M. volkensii and S. Spectabilis exhibited similar leafing phenology patterns, losing almost all leaf cover during the long dry season (July-October) and flushing before the ensuing rains. During the short dry season, S. spectabilis lost few leaves, whilst M. volkensii lost some leaves before flushing prior to the onset of the long rains. M. volkensii lost a large proportion of its leaf cover during the 1997/98 short rains due to the unusually high soil moisture content. C. megalocarpus although predominantly evergreen, lost a large proportion of its leaves during dry periods, whereas leaf area increased rapidly under wetter conditions. G. sepium had one annual period of low leaf cover during the long dry season and did not regain full leaf cover until mid-way through the short rains. The three-dimensional model of canopy photosynthesis and transpiration, MAESTRA, was parameterised for C. megalocarpus and M. volkensii using existing models to describe the response of photosynthesis to light and temperature and stomatal responses to light and vapour pressure deficit. The photosynthesis model fitted the experimental data well, but stomatal conductance in C. megalocarpus, although showing responses to light and vapour pressure deficit, was not closely correlated with ambient environmental conditions. M. volkensii had higher leaf area than C. megalocarpus for most of the 18 month simulation period, comprising three rainy and three dry seasons; modelled assimilation for this period was 49 % greater in M. volkensii, while canopy water use efficiency and transpiration were respectively 35 and 11 % higher. These differences accounted for the more rapid growth rate and greater competition with adjacent crops associated with M. w1kenrii relative to C. megalocarpus. Above-ground woody biomass production was greatest in M. volkensii, followed by S. spectabilis, C. megalocarpus and G. sepium; production during the fourth and fifth years after planting ranged between 2.8 and 4.9 t ha-¹ yr¹. Crop production in the agroforestry treatments was always lower than in sole crops due to below-ground competition for water and, in seasons with higher water availability, shading by the trees. Of the agroforestry systems examined, seed production for beans was highest under M. volkensii and G. sepium, followed by C. megalocarpus and S. spectabilis. Grain production in maize was greatest under C. megalocarpus, followed by G. sepium, S. spectabils and M. volkensii. Mean annual aboveground biomass production including maize grain and stover, bean seed, woody biomass and tree leaves in the M. volkensii treatment exceeded that for the sole crop plots, even though rainfall during 1996 and 1997 was only 61 and 95 % of the long term average. Although the biomass production of leaves was not estimated for S. spectabilis and G. sepium, the results obtained suggested that biomass production was greater than that obtained under sole crop cropping. The inverse correlation between tree and crop yield suggests that the value of the tree products must exceed the associated crop losses if benefits are to be obtained from agroforestry. M. volkensii is valued in areas of Kenya where markets for its products exist and therefore shows great promise for extension in semi-arid areas; where necessary, pruning may be used to reduce competition with crops and increase the length of clear bole. C. megalocarpus is widely used as a shade tree in East Africa and seems well suited for this purpose as its impact on adjacent crops was least of all the tree species examined. S. spectabilis, although having straight unbranched stems, exhibited a level of competition with adjacent crops that would necessitate a high value for its timber products to warrant its adoption. The least suitable tree species of those examined was G. sepium, whose poor form and susceptibility to attack by fungal pathogens and insects severely undermined its potential value for use in agroforestry systems.

The aim of this project was to develop azadirachtin as an insecticide that is applied to the soil, using a granular formulation, for root uptake and subsequent systemic plant protection. A method was developed whereby azadirachtin could be rapidly isolated to approximately 95% purity using flash chromatography. This material was used in all subsequent chemical and biochemical studies. To increase the speed of crude extract analysis, a colorimetric technique was assessed to rapidly quantify azadirachtin. However, this method was generally unsuitable for the requirements of this project because it was non-specific and not stable. Granular formulations based on sodium alginate, starch-kaolin and poly(e-caprolactone), and containing different neem seed extracts were successfully prepared. These granules exhibited differnces in the rate of azadirachtin release into water. Additives such as kaolin clay and rapeseed oil could be used to modify the speed of release. Following application to soil, the position of granules did not affect release rates. However, granule application method was shown to affect the rate at which the limonoid was accumulated within the nasturtium plants. Azadirachtin was shown to be moderately water-soluble (1.29 g/l). During mixing studies between distilled water and n-octanol, the limonoid partitioned more favourably into the non-aqueous phase at a ratio of 7:1. Based on calculated Koc values (<40), azadirachtin was classified as very highly soil mobile. Adsorption occurred principally to the organic matter of soils. Clay minerals were comparably non-sorbent. Desorption from both of these sites occurred readily. Azadirachtin was not persistent within soil where the limonoid’s DT50 was as short as 1.06 days. Initial breakdown resulted in the acetyl moiety being cleaved from the molecule. In addition, azadirachtin was shown to exhibit a pH sensitive hydrolytic degradation. The limonoid’s half-life in solution ranged from 57 days at pH 5 to 7.15 hours at pH 9. In conclusion a suitable granule for a controlled-release of azadirachtin was developed.

Many species of moths within the family Noctuidae are significant agricultural pests. Specific floral volatiles are attractive to both male and female Noctuidae and may be used to as attractants in crop protection. For the first time the following research compares two types of floral volatile blends - those that mimic natural floral odours and those that are artifical odour blends ('super-blends'). In wind tunnel bioassays and field trials in two diverse geographic locations (Argentina and the United Kingdom) a range of noctuid moth species that are considered crop pests were found to be attracted to both types of the floral odour blends. However, a 'super-blend' containing phenylacetaldehyde, salicylaldehyde, methyl 2-methoxybenzoate, linalool, and limonene (in a 10 : 4 : 2 : 2 : 1 ratio) was found to be the most effective general attractant across the following species: Helicoverpa armigera and gelotopoeon, Heliothis zea, Spodoptera frugiperda, and Autographa gamma suggesting that these compounds are universal cues to this family of moths when searching for flowers. Further behavioural bioassays found that the physiological state of the insect had an important effect on its behavioural response to the floral odour super-blend. Bioassays carried out on H. armigera revealed that gravid insects were significantly less likely compared to virgin insects to make contact with an odour blend baited lure. In addition, insects provided with sucrose solution were significantly less likely to make contact with the odour source compared to starved insects or insects only provided with water. This is the first time this affect has been seen in this species and may have important implications for using these types of floral odours for crop protection. Investigations into the most effective trap for capturing Noctuidae found that a homemade bucket and water trap or funnel and sleeve traps were significantly more effective than UniTraps or sticky traps. During the field trials large numbers of nontarget insects were also captured, including beneficial insects and pest species. By using green coloured traps captures of beneficial hymenoptera (Syrphidae and Apoidea) were significantly reduced. Taken together, the current findings provide insights into how Noctuid moths interact with host odour cues and how they may be used in developing pest management techniques.

The case for improving Phosphorus-Use Efficiency in crops is widely recognised. Although much is known about the underlying molecular and regulatory mechanisms, improvements have been hampered by the extreme complexity of phosphorus (P) dynamics in soil and plants (across all physical scales), including its soil chemistry and uptake, distribution and deficiency responses in plants. The urgency and direction of phosphate research is also being driven by the availability of finite P stocks to farmers and reducing environmental hazards. Thus, systems approaches become essential to identify the most potent (combinations of) target genes for improving phosphate uptake and utilisation in crops. This study has applied these approaches with the aim of increasing understanding of the regulation of phosphate uptake at three separate spatial scales, primarily in rice, but also in Arabidopsis. The first and major part of this study has focused on the cell scale, wherein novel mathematical models for molecular regulation of phosphate acquisition have been developed. Owing to the sparsity of the data, advanced techniques for parameter fitting were employed, which resulted in an original model, which accurately reflected the profiles of all the genes apart from PHO2. It was clear that miR399-mediated degradation was insufficient to explain the apparent early reduction in PHO2 mRNA levels. Five hypotheses were explored mathematically, of which the most plausible is that there is a phosphate-sensitive transcriptional repressor (PsTR) of PHO2 mRNA synthesis. To support this hypothesis, mRNA was extracted from phosphate-starved and untreated roots over a short, 12-hour time course. Quantitative Polymerase Chain Reactions (qPCR) of PHO2 mRNA both confirmed the early decline predicted by the hypothesis and also revealed a temporary restoration of mRNA levels, which points to PHO2 (a type-2 ubiquitin ligase) regulating its own transcript levels. Sensitivity analysis of these models indicates that the utilisation rate of cytosolic phosphate is the biggest influence on this system. Output from simulations with the original and PsTR models qualitatively reproduced the phenotypes of various published phosphate-research papers, with the exception of RNASEQ data in which phosphate-starved rice roots were resupplied with phosphate. In this instance, the observed rapid drop in mRNA levels for PHO2 and IPS1 were incorrectly predicted, pointing to one or more other regulatory mechanisms not represented in these models. The IPS1 gene encodes a long non-coding RNA that has a poly-A tail. Its RNA also binds to miR399 and accumulates to extremely high levels in plant roots during phosphate stress. A sudden loss of IPS1 would release the bound miR399 causing the observed rapid loss of PHO2 mRNA. The observed IPS1 profile can be explained by either the gene having a “super-promotor” that is capable of extremely high RNA synthesis under low phosphate conditions, or the transcript being protected from degradation by phosphate-sensitive RNA-binding proteins. Informatics analyses favour the latter and a revised model incorporating RNA protection was found to have parameters for IPS1 synthesis that are similar to those normally used in modelling gene regulation. The analyses also point to PUMILIO proteins playing this role. The second part of this work has explored the role of tissue geometry in determining root phosphate levels and flux. Multi-cellular vertex-based models of published Arabidopsis and rice root cross-sections were produced using CellSeT, into which equations for phosphate uptake, flux and utilistion were embedded using OpenAlea. Simulations suggest that Arabidopsis trichoblasts have lower cytosolic phosphate levels than neighbouring epidermal cells, because they have a larger area through which phosphate flows into the inner tissues. This implies that trichoblasts are more sensitive to phosphate stress and reduced phosphate levels could therefore be part of the trigger for initiating root-hair growth. Adding root hairs of varying lengths into this geometry shows that a hair does not have to grow much before the phosphate levels in this trichoblast exceeds those in the neighbouring cells and that phosphate flows to them. This potentially suppresses root-hair formation in nearby trichoblasts. The rice simulations show that aerenchyma dramatically reduces cytosolic phosphate in surrounding cells and point to a role for lacunae in rapid uptake of phosphate, without the need for large water fluxes. Alongside aerenchyma, a higher proportion of fluid-filled lacunae could be a desirable trait for improving nutrient-uptake efficiency. At the whole-plant scale for the third part of this work, a time-course dataset has been generated to record the effect of phosphate starvation over 21 days on the uptake dynamics of eleven other macro- and micro-nutrients. This dataset will be of use in future systems studies of nutrient uptake and interactions.

The baobab tree (Adansonia digitata L.), with more than 300 uses and commercial value in EU and US, has been identified as one of the most important edible savannah trees to be conserved, domesticated and valorised in Africa. A decline in baobab populations due to overexploitation and/or changes in climate could have a significant negative effect on African livelihoods. Therefore, it is important to determine potential strategies for conservation and cultivation. The present and potential future distributions of the baobab tree were studied using Maxent niche modelling framework. And, in order to contribute to the selection of superior materials for cultivation, fruit morphology was studied in situ (in Malawi and Mali) while leaf and seedling morphology were studied in situ (in Benin and Malawi) and in a greenhouse experiment. Maxent modelling suggests that predicted changes in climate will have a negative effect on baobab tree distribution in Africa: only a percentage of the present distribution was predicted to be suitable in the future. Some countries were found not to have any suitable habitats for the baobab tree in the future. Several conservation strategies are recommended, such as in situ conservation in Protected Areas; ex situ conservation in Seed Banks and conservation through ‘sustainable utilisation’. Modelling results also showed that the baobab tree could be widely cultivated in most countries in south-eastern Africa and in the Sudano-Sahelian zone of West Africa. India, north-west Australia, Madagascar, north-east Brazil and Mexico could be other suitable places for cultivating the baobab tree outside Africa. Although results from modelling should be validated with in situ seedling experiments, there seems to be potential for the wide cultivation of this species. Significant differences in leaf, fruit and seedling morphology were observed between Benin, Mali and Malawi and also within each country. While some characteristics were correlated with environmental differences between study sites, others might be genetically determined. It seems that genetic and physiological effects play a role in baobab fruit, leaf and seedling morphology. Thus, there is room for selecting high quality baobab planting materials

The aim of the thesis is to contribute to our understanding of how individuals in developing countries cope when faced with environmental risks. These themes are explored while focusing on small-scale farming communities in Wellawaya, south-east Sri Lanka, that are heterogeneously exposed to a particular environmental risk, namely the Human-Elephant Conflict (HEC). First, we examine the strategies which households within farming communities use to cope with exposure to the HEC. We conduct an individual-level household survey of 468 randomly-sampled households across sixteen farming communities which are highly exposed to the HEC. Our unique, cross-sectional data provides a snapshot of the coping strategies which they employ. We find that households which experience greater HEC-related damage are more likely to: rely to a greater extent on non-farm income; cultivate less land in each of the two cropping seasons; and have children who engage in non-farm employment. Next, we investigate the effect of interdependent risk exposure on individuals’ ex-post sharing behaviour. By interdependence, we refer to when an individual’s choice over their own risk exposure directly impacts the risk exposure of another individual. The results from our lab-type risk-and-sharing game suggest that individuals positively reciprocate when another individual’s decision causes them to face lower risk exposure, but do not negatively reciprocate when another individual’s decision causes them to face higher risk exposure. A risk-averse individual who has agency over another’s risk exposure is more likely to share ex-post payoffs, while a relatively risk-tolerant individual does not. Our results suggest that risk attitudes and the balance of power within communities need to be considered by policymakers involved in the design of community-driven development initiatives. Finally, we adopt a mixed methods approach to investigating how heterogeneity in individual returns to a public good and beneficiaries’/contributors’ risk attitudes affect public good contributions. We examine this in the context of Sri Lanka’s HEC and conduct a one-shot, framed, lab-in-the-field, public goods experiment (PGG) which reveals subjects’ contribution preferences when returns from the public good are asymmetric. Subjects also answer a hypothetical contribution question (HCQ) stating their time contributions to the construction of the public good. We find that heterogeneity in individual returns does not have a negative effect on contribution behaviour. Risk-aversion in the PGG, in this context, motivates people to engage in collective risk mitigation. The mixed method approach provides an encouraging and balanced account of communities’ potential engagement in HEC-mitigating public goods provision.

Rhizobia are frequently used in the agriculture sector to enhance legume growth and improve soil fertility. There is growing interest in utilizing biological nitrogen fixation as a means of increasing the potential for sustainable intensification of food production whilst simultaneously reducing environmental damage caused by overuse of chemical fertilisers. Biochar, a recalcitrant carbon-rich product of pyrolysis which may be added to soil as a fertilizer or as a soil improver, alters soil physico-chemical properties usually by acting as a liming agent, by increasing water holding capacity or by modifying cation exchange capacity. The effects of biochar on the soil microbial community are not fully understood. Therefore, the main aim of this investigation was to evaluate the effects of biochar on the Rhizobium-legume relationship and determine whether biochar could increase legume growth. To achieve this aim, a series of growth experiments were carried out under controlled conditions in which broad bean (Vicia faba) was grown with Rhizobium leguminosarum and the symbiosis tested against three concentrations of biochar applied as a soil amendment and with two different char particle sizes. Beans responded well to Rhizobium under char-free conditions but the effects of biochar on the symbiosis were variable and depended on char particle size, concentration and Rhizobium strain (commercial or indigenous). Powdered char inhibited plant growth when in the presence of the commercial rhizobia, but not with indigenous strains. This is an important finding since commercial inocula are commonly used in agronomic situations. Plant available soil nutrients were modified by biochar and surprisingly by an interaction between char concentration and the two rhizobia strains. When beans were co-cropped with wheat, beans performed better when grown with powdered char than without. This is in contrast to the response of bean plants to powdered char in the absence of any competition. Since wheat was generally the superior competitor, powdered char amendment enabled the bean to take advantage of the N-limiting environment that powdered char created and perform better than in the soils that advantaged the wheat. The investigation highlighted the complexity of the system, but identified the importance of char particle size and Rhizobium strain selection.

This study investigated the simulated impact and vibration tests on bruise damage and quality of the British strawberries from winter and summer cultivations. The actual transport of food products was also monitored for the vibration and temperature levels in the city and highways. The winter cultivation produced a superior overall quality of 'Elsanta' and 'Sonata' strawberries compared to the summer cultivation. 'Sonata' fruits were more sensitive to vibration damage in the summer cultivation. The packed strawberry punnet of 250 g was tested in impact and vibration tests. The maximum drop height at 750 mm gave a significantly larger wet bruise level of around 40% than other drop heights (p.0.05). The simulated vibration investigated the three frequencies and three exposure times plus control. The vibrated fruits from the most severe of 5 Hz (1.1 g) for 150 sec had significantly higher wet bruises (50-60%) than for other treatments (p.0.05). The bruise damages increased for both simulated tests after storage at 10°C, 70±5% RH for 3 days. The EC value gave a significantly stronger correlation with wet bruise and severity score as compared to puncture, compression and respiration rate measurements (p.0.01). The EC method is suggested for use as a rapid indicator and a predictor for the bruise assessment of strawberries. The vibration and air temperature levels in the refrigerated truck and semi-trailer were monitored. The overall peak frequency of power density was often found at 10-14 Hz. The vertical vibration was the dominant direction during the road transport. The rear-top position gave a stronger root mean square acceleration value. A gradual increase of vibration level occurred after the first drop in city distribute as well as for a smaller load. The range of temperature during food transport was around 2 to 8oC with a set point at 3°C.

The Agricultural Development Fund (ADF) is the Government agency responsible for financing farmers in the Saudi Arabian agricultural sector. The ADF provides short-term loans and medium-term loans and funds specialised projects, as well as providing subsidies for some types of loans. From its establishment in 1962 until 2012, the ADF has lent more than £7.7 billion and the total number of loans exceeds 439,000. However, in spite of the facilities provided by the ADF, its annual reports show that the outstanding debt increased from £579 million in 1990 to £840 million in 2012; moreover, the reports reveal that some project areas have been receiving more funding than others. This thesis aims to assess the efficiency of the collection of loan repayments by the ADF. This aim will be achieved through four objectives: 1) analyse the current status of the regional distribution of agricultural loans to determine the optimal distribution of loans among regions to achieve development objectives, 2) examine the determinants of the efficiency of loan collection to identify and quantify factors that affect loan repayment, 3) explain the variation in collection rates among the ADF's branches and 4) provide recommendations to improve the probability of repayment and achieve the optimal distribution of loans. Variation in the current distribution of agricultural loans among regions has been observed. Using Multiple-Attribute Analysis, this variation has been identified as sub-optimal with respect to achieving development objectives. The highest priority regions for agricultural loans are the Northern, Jazan and Baha regions. Logistic modelling approaches have been used to determine factors affecting the repayment of short-term loans, medium-term loans and specialised projects; the empirical results of the overall model for short-term loans show that the age of the borrower and four regions have a positive significant effect on loan repayments, while the grace period, the loan value, the financial guarantee and three regions each have a significant negative effect. The results of the analysis of medium-term loans reveal that five variables have a significant effect on loan repayments: age, the grace period and loan value have a negative effect. Financial guarantee and three regions have a positive effect. The results for the specialised projects showed that the Hail region, feed and wheat project have a positive effect, while the Eastern region and greenhouses, livestock and vegetables projects have a negative effect on loan repayments, whereas the age of the borrower, the grace period, financial guarantee and loan value have no significant effect.

A total of five studies were conducted to determine the nutritional value of co-products of bioethanol production for poultry and pigs. The objective in the first study was to evaluate the relationship between the chemical components of maize- and wheat distillers dried grains with solubles (DDGS) as well as develop prediction equations for indispensable amino acids (IAA), total indispensable amino acid (TIAA) and total amino acid (TAA) contents using nutrient composition data available in literature. The relationship between the chemical constituents of maize- and wheat-DDGS and associated probability values were determined by correlation analysis. Prediction models for determining the IAA, TIAA and TAA contents of maize- and wheat-DDGS from their crude protein (CP) and amino acids (AA) contents were developed using step-wise multiple regression analyses. Maximum improvement in adjusted r2 (adj r2) and reduction in Mallows Cp were the model selection criteria. The chemical composition of maize- and wheat-DDGS varied among sources with coefficient of variation (CV) ranging from 8.5% to 53.5% for total P and Ca respectively in maize-DDGS and 10.5% to 36.1% for CP and acid detergent fibre (ADF) in wheat-DDGS respectively. Of the IAA, Lys, Met and Trp were most variable in maize-DDGS with CV of 13.1%, 12.0%, 10.3%, respectively, whereas Lys, Phe and Met were the most variable IAA in wheat-DDGS with CV of 20.2%, 17.3%, and 16.9%, respectively. For maize-DDGS, there were positive correlations (P < 0.05) between CP and CF, NDF, Ca, ash (r ranged from 0.45 and 0.61). Adjusted r2 ranged from 0.57 to 0.99 in the best models for predicting the IAA in maize- and wheat-DDGS from CP and AA. Except for Trp and Lys, the IAA contents of maize- and wheat-DDGS can be predicted from their CP content alone. The best models for predicting TIAA and TAA in maize-DDGS included Arg, His and Leu (adj r2= 0.98) and His, Leu and Trp (adj r2= 0.90) respectively, the regression equations being TIAA (% DM) = 0.77 + 1.36 (Arg) + 3.87 (His) + 1.99 (Val) and TAA = -3.03 + 14.1 (His) + 3.79 (Leu) + 23.4 (Trp) respectively. For wheat-DDGS, the best three variables for predicting TIAA were Arg, Leu and Val (adj r2=0.99), the regression equation being TIAA (% DM) = -0.07 + 1.11 (Arg) + 0.99 (Leu) + 5.02 (Val). Predicted values were close to actual values in the prediction models for IAA, TIAA and TAA. It was concluded that the IAA, TIAA and TAA contents of both maize- and wheat-DDGS can be predicted from their CP contents with high accuracy. In the second study, the nutritional value of wheat-DDGS without- or with exogenous enzymes for broiler was determined using three experiments. The N-corrected- and apparent metabolisable energy contents (AMEn and AME, respectively) without- or with added admixture of xylanase, amylase and protease (XAP) was determined in experiment 1, true P digestibility without- or with supplemental phytase was determined in experiment 2, whereas the apparent- or standardised ileal digestibility (AID and SID, respectively) of AA without- or with added protease was determined in experiment 3. Birds were fed a nutrient adequate pre-experimental diet from d 1 to 14 post-hatch followed by the dietary treatments from d 14 to 21 in experiment 1 and 2, or from d 25 to 28 in experiment 3, respectively. Each of the 3 experiments was arranged as a randomised complete block design consisting of 7 replicate pens and 3 birds per pen. Six dietary treatments consisting of 3 levels of wheat-DDGS (0, 300 or 600 g/kg of diet) and 2 levels of XAP (0 or 0.25 g/kg) were used in experiment 1. Six diets consisting of 3 levels of wheat-DDGS (200, 400 or 600 g/kg of diet) and 2 levels of phytase (0 or 1000 FTU/kg) were used in experiment 2, whereas four treatments consisting of a nitrogen-free diet (NFD) and an assay diet, both diets without- or with supplemental protease were used in experiment 3. In experiment 1, increasing the level of wheat-DDGS in the basal diet decreased linearly (P < 0.001) dry matter (DM) and energy retention, AME and AMEn. Supplemental XAP tended to improve both the dietary AME (P = 0.059) and AMEn (P = 0.085) values of the diet. The AME value of wheat-DDGS without- or with supplemental XAP was determined to be 15.0 or 15.5 MJ/kg, respectively. Corresponding values for AMEn were 14.0 and 14.5 MJ/kg, respectively. Supplemental XAP did not improve the energy value of wheat-DDGS for broilers. In experiment 2, increasing the level of wheat-DDGS in the diet decreased linearly (P < 0.05) ileal DM digestibility, DM retention and apparent P retention but there was no difference in apparent ileal P digestibility. Except for Fe and Zn at the ileal, and Mn and Zn at the total tract level, increasing the level of wheat-DDGS in the diet increased linearly (P < 0.05) the flow of all other minerals. Flow of minerals at the ileal and total tract level were not different with phytase supplementation. True ileal P digestibility in the wheat-DDGS for broilers was 93.6 or 96% without- or with added phytase, respectively. Corresponding values at the total tract level were 92.4 and 93.5%, respectively. Phytase addition did not improve P utilisation at the ileal or total tract level. In experiment 3, AID ranged from 33% (Asp) to 75% (Pro) without added protease whereas the range was 31% (Asp) to 82% (Pro) with protease supplementation. The AID of Lys was nil regardless of protease supplementation. Supplemental protease improved (P < 0.05) the AID of Arg and Pro and tended to improve (P < 0.10) the AID of Met. Without protease supplementation, SID ranged from 43% (Asp) to 84% (Pro) whereas the range was from 54% (Asp) to 93% (Pro) with added protease. Supplemental protease improved (P < 0.05) the SID of Arg, Leu, Phe, Met, Val and Pro by 21, 14, 13, 26, 13 and 10 percentage points, respectively. It was concluded that wheat-DDGS is a good dietary source of metabolisable energy and P for broilers. The ileal AA digestibility of wheat-DDGS for broilers is quite variable and generally low. Further, the ileal digestibility of some AA in the wheat-DDGS improved with protease supplementation. Using three experiments the third study determined the metabolisable energy content, true P digestibility and retention and AIAAD and SIAAD of wheat-DDGS for turkey. The AMEn and AME content of wheat-DDGS without- or with XAP was determined in experiment 1, the true P digestibility and retention without- or with supplemental phytase was determined in experiment 2, whereas the AIAAD and SIAAD of wheat-DDGS without- or with a protease were determined in experiment 3. Experiment 1 and 2 lasted for 21 days whereas experiment 3 lasted for 28 days. Experimental diets were fed for 7, 5 or 3 d in experiment 1, 2 or 3, respectively. Each of the 3 experiments was arranged as a randomised complete block design consisting of 7 replicate pens and 3 birds per pen. Six dietary treatments consisting of 3 levels of wheat-DDGS (0, 300 or 600 g/kg of diet) and 2 levels of XAP (0 or 0.25 g/kg) were used in experiment 1. Six diets consisting of 3 levels of wheat-DDGS (200, 400 or 600 g/kg of diet) and 2 levels of phytase (0 or 1000 FTU/kg) were used in experiment 2, whereas four diets consisting of a NFD and an assay diet, both diets without- or with supplemental protease were used in experiment 3. In experiment 1, increasing the dietary inclusion of wheat-DDGS from 0 to 600 g/kg decreased linearly (P < 0.05) DM and energy retention. There was wheat-DDGS × XAP interaction (P < 0.05) for dietary AME and AMEn. Dietary AME and AMEn values decreased linearly (P < 0.001) as the level of wheat-DDGS increased in the diets without XAP, whereas there was no effect of increasing wheat-DDGS level on dietary AME or AMEn for the XAP-supplemented diets.