Examples of response surfaces for pairs of nutrients and results of 41 multi-level experiments with N only were used to compare the goodness-of-fit of polynomial, inverse polynomial, exponential and intersecting-straight-lines models. Whereas no one model fitted best at every site, many results were well represented by two intersecting straight lines and on average, this model had the least residual mean square. Of 17 experiments with spring barley in south western England the few results best represented by smooth curves were from crops much affected by leaf diseases.Fertilizer response was poorly represented by models without a falling asymptote, like the simple exponential and inverse linear. Study of residuals after fitting the quadratic showed that this widely used model consistently over-estimated both the amount of fertilizer needed for maximum yield and the yield loss when too much fertilizer was given.When fitted to the mean yields of each nitrogen treatment, most models had residual mean squares equal to or less than the error mean square, repeating a result obtained at Rothamsted as early as 1927. We question the validity of some well-known evidence for block and treatment additivity.For 12 experiments in 1970, between-site differences in the parameter values of the two straight lines representing grain yield were related to leaf area at ear emergence.TNTTT? onnrTTO'Nr series of experiments, each experiment testing many levels of one or more nutrients. Instead of estimating Most of the experiments discussed in this and the the effects of individual treatments and their following paper result from important develop-significance, the main object is to determine the ments in experimental methods in the past decade, optimal dressing (or, with several nutrients, their In crop nutrition these changes have resulted optimal combination) and to discover how and why mainly from soil scientists' need to make their fertilizer requirements differ from place to place advice to farmers increasingly precise and at the and from year to year. This paper discusses the form same time less empirical as a result of improved of response curve relating crop yield and fertilizer understanding of plant:soil relationships. Greater input, based mainly on results of multi-level nitroattention has been paid to planning, whereby site gen experiments with cereals, selection is related to soil and husbandry factors likely to influence fertilizer requirements, and there The need f or f resh information on fertilizer response has been more thorough and more uniform recording curves of these and other external factors. The isolatedThe average results of experiments with sugar experiment with few treatments and treatment beet, testing different amounts of N fertilizer, were levels but much replication has been replaced by well fitted by a quadratic response curve, but when

Tho effect of nitrogen fertilizer on the yield of sugar beet was tested in 170 experiments done between 1957 and 1966; results of 88 experiments, some testing five and six amounts of N, have not previously been published.On most sites, nitrogen increased sugar yields sharply and almost linearly up to an optimum beyond which yield changed little or decreased only slightly up to 1-8 cwt N/acre, the largest amount tested. In the two series of experiments giving most information, the mean increase from sub-optimal amounts of N was 2-5 cwt sugar/0-1 cwt N/acre.Usually 0-4-0-8 cwt N/acre was enough for maximum yield; more was needed on a few sites and on about a fifth of them nitrogen fertilizer was not needed. In 7 of the 10 years, the average optimum was 0-6-0-8 cwt N/acre; less was needed in the other years, the driest three years of the decade.In most, though not all, years, site-to-site differences in response between 0-9 and 1-8 cwt N/acre were no greater than could be expected from experimental error alone; much of the apparent difference in response between seasons were also attributable to this source.After taking account of experimental error, there were substantial between-site differences in response to amounts ofNup to 0-9 cwt/acre, but attempts to explain them in terms of weather, soil and husbandry factors had little success. There was slight evidence of diminished responses to N where sugar beet followed crops other than cereals, and of responses somewhat greater than average on Chalky Boulder Clay soils of the Hanslope and Stretham Series; no other relationships were large or consistent enough to be useful for prediction.As between-site differences in response are largely unpredictable, and because a grower risks much greater crop losses by applying too little N than by applying too much, the recommended dressing is 1-0 cwt N/acre, substantially more than is needed, on the average, to obtain maximum yield. More N should be given on soils of the Hanslope and Stretham Series and on light sands poor in organic matter; less need be applied where crop residues are likely to supply much nitrogen. less than this on fields ploughed up from grass and somewhat less on fields given farmyard manure The nitrogen requirement of sugar beet grown on (FYM). From the results of 41 experiments done in mineral soils has been studied in many experiments 1957 -60, Adams (1962 found the optimum to be in Great Britain during the past 30 years. Sum-1-0 cwt N/acre where the beet followed two or more marizing the results of 360 experiments done be-cereal crops but only about 0-6 cwt N/acre after tween 1934and 1949,Boyd,Garner&Haines( 1957) other crops, or where FYM was applied; 1-8 cwt concluded that, in each factory area, the mean op-N/acre often gave less yield than 1-2 cwt N/acre. timal dressing was 1-0-1-2 cwt N/acre, but was much From 42 experiments done between 1959 and 1962,

The paper describes the results of over 300 factorial experiments carried out in each factory area in the years 1934–49 for the Sugar Beet Research and Education Committee of the Ministry of Agriculture as a result of co-operation between Rothamsted workers and the agriculturists and fieldmen attached to the beet factories. All the experiments tested the effects of levels of nitrogen, phosphate and potash, and rather more than half tested the effect of salt also.Except on fen soils, nitrogen gave substantial responses in all factory areas, especially in the presence of high levels of potash or salt. Large variations in response from season to season were closely associated with the rainfall of the preceding winter months, responses being greater after wet winters than dry ones.In spite of some selection of sites in favour of greater responses, the average net returns from phosphate were relatively small.The effect of potash was closely linked with the amount of nitrogen applied; in the presence of nitrogen, dressings well above the level of 1·2 cwt. K2O per acre tested in the experiments are likely to give a useful net return. Soils derived from the Chalky Boulder Clay seem to be exceptional in showing no response. Apart from this, there were only small variations in responses to nitrogen and potash between factory areas. The application of 5 cwt. salt gave substantial responses in almost all parts of the country, whether or not potash was also applied; on the other hand, responses to potash were usually small when salt was also applied.Whilst there was a general relationship between soil analysis for phosphate and potash (citric acid method) and crop response, adjustments to the optimal dressings according to soil analysis were not of sufficient reliability to be of much practical value.

Intensifying livestock production by integrating perennial forages has great potential to contribute to sustainable development and livelihoods in the Mekong region. However, the approach taken must be informed by the environmental, social, and cultural context of the region. Accordingly, we review published research papers and reports from relevant research for development projects to identify options for sustainably integrating forages into farming systems, with a focus on sand-dominant soils of southern Laos and Cambodia. First, we examine existing livestock management practices to determine the compatibility of forages as an option to intensify livestock production. Second, we review the environmental properties of rainfed lowland rice systems with sandy soils and their implications for forage growing. Third, we identify and compare the suitability of existing forage genetics that is adapted to these environmental properties. Fourth, we propose adapted varieties, outline appropriate management options, and discuss the sustainable engagement of smallholders in the production of forages. The key findings are as follows: (1) Forages appear compatible with the sociocultural properties of smallholder farming systems in southern Laos and Cambodia because there is an awareness of existing limitations to livestock production, widespread desire to possess livestock for cultural reasons, and mounting pressure to improve the productivity of grazing areas and the efficiency of labor.(2) The limiting properties of the environment are drought, soil acidity, flooding, and soil infertility, which must be addressed in the selection and management of forage genetics. (3) Broadly adapted perennial tropical grasses and herbaceous legumes exist, but these are unlikely to thrive in lowland ecosystems of southern Laos and Cambodia that are prone to both annual flooding and drought. (4) Variations in surface hydrology at the farm scale often result in differentiated environments suitable for differing varieties. Brachiaria sp. hybrid "Mulato II," Panicum maximum, and Stylosanthes guianensis are recommended for droughtprone, acidic sands that are safe from prolonged submergence and would require the least additional management, whilst Paspalum atratum is recommended for low-lying areas with access to irrigation. (5) The transition to perennial forage integration appears to be accessible to farmers and can allow them to rapidly accumulate benefits in terms of saved labor; however, efforts to intensify animal production have been slow and must contend with multiple challenges: poor understanding of animal husbandry and health, cultural views relating to the role of animals in production systems, and poor access to forage and livestock services. These must all be addressed if sustainably intensified animal production is to be achieved in these and similar regions.

Purpose-Interdisciplinary approaches to climate change teaching are well justified and arise from the complexity of climate change challenges and the integrated problem-solving responses they demand. These approaches require academic teachers to collaborate across disciplines. Yet, the fragmentation typical of universities impedes collaborative teaching practice. This paper aims to report on the outcomes of a distributed leadership project in four Australian universities aimed at enhancing interdisciplinary climate change teaching. Design/methodology/approach-Communities of teaching practice were established at four Australian universities with participants drawn from a wide range of disciplines. The establishment and operation of these communities relied on a distributed leadership methodology which facilitates acts of initiative, innovation, vision and courage through group interaction rather than through designated hierarchical roles. Findings-Each community of practice found the distributed leadership approach overcame barriers to interdisciplinary climate change teaching. Cultivating distributed leadership enabled community members to engage in peer-led professional learning, collaborative curriculum and pedagogical development, and to facilitate wider institutional change. The detailed outcomes achieved by each community were tailored to their specific institutional context. They included the transformation of climate change curriculum, professional development in interdisciplinary pedagogy, innovation in student-led learning activities, and participation in institutional decision-making related to curriculum reform. Originality/value-Collaborative, non-traditional leadership practices have attracted little attention in research about sustainability education in university curricula. This paper demonstrates that the distributed leadership model for sustainability education reported here is effective in building capacity for interdisciplinary climate change teaching within disciplines. The model is flexible enough for a variety of institutional settings.