ALBERT

Description: Abstract Quantification of climate forcing of glacial hydrological systems at the decadal scale are rare because most measurement stations are too far downstream for glacier impacts to be clearly detected. Here, we apply a measure of daily hydrograph entropy to a unique set of reliable, high altitude gauging stations, dating from the late 1960s. We find a progressive shift to a greater number of days with diurnal discharge variation as well as more pronounced diurnal discharge amplitude. These changes were associated with the onset of rapid warming in the 1980s as well as declining end of winter snow depths as inferred from climate data. In glaciated catchments, lower winter snow depths reduce the magnitude and duration of snowpack buffering and encourage the earlier onset of glacier ice exposure, with associated lower surface albedo and more rapid melt. Together, these processes explain the increase in the observed intensity of diurnal discharge fluctuations.

Description: SUMMARYDuring 1899–1964 various levels of 0·5 M sodium bicarbonate-soluble P had been established in an experiment on a sandy clay loam (pH 6·5–7·0) at Saxmundham, Suffolk. Modification made between 1965 and 1968 widened the range of soluble P values to 3–67 mg/kg. Relationships between these soluble P values and yields of potatoes and sugar beet in 1969–74 and cereals in 1970–7 were assessed. Responses by potatoes and sugar beet to freshly applied superphosphate were also determined at each level of soluble P. Residual effects of these dressings and responses to fresh superphosphate between 1974 and 1976 were measured by barley. Two amounts of N were tested on spring barley in 1976–7 and two cultivars of winter wheat were grown in 1977 and yields related to soluble P.Relationships between yields and soluble P were described by an asymptotic regression equation. This model represented the measured yields well for all crops except barley, in one 4-year-period, when there were insufficient data at low soil P values and a linear regression model was fitted. The asymptotic model was used to estimate plateau yields each year and soluble P values at which yields were less than plateau values by one standard error. Average plateau yields, and associated soluble P values were: potatoes, 43 t/ha and 25 mg P/kg; sugar (from sugar beet) 6·8 t/ha and 20 mg P/kg; spring barley, given 63 kg N/ha, 4·7 t/ha and 25 mg P/kg; barley given 94 kg N/ha, 5·3 t/ha and 33 mg P/kg; winter wheat, 6·5 t/ha and 20 mg P/kg.The model was further used to estimate responses to dressings of superphosphate at three levels of soluble P (9, 15 and 25 mg/kg) in the soils. Yield responses to 55 kg P/ha were 3·9, 2·1 and 1·8 t tubers/ha and 1·1, 0·3 and 0·0 t sugar/ha, for potatoes and sugar beet respectively, at the three levels of soluble P.On impoverished soils (soluble P 〈 10 mg/kg) even the largest fresh applications of broadcast superphosphate did not raise yields to those achieved on enriched soils (soluble P 〉 25 mg P/kg) in the absence of fresh phosphate.Soluble P in the soils accounted for much of the within-year variation of yields and estimated reliably and quantitatively the value of phosphate residues derived from both superphosphate and farmyard manure which had been applied in varying amounts and at different times between 1899 and 1976.

Description: SUMMARYThe largest yields of wheat and potatoes came from the combination of longer ley plus optimum fertilizer N but yields of winter beans were decreased where N had been given to the previous crops. Without fertilizer N, two year old leys significantly increased yields compared to one year leys and the effect of longer leys was small except for the first wheat, when grain yields were large and plateaued after the three year ley.Exponential response curves were fitted to the wheat yields and an exponential plus linear trend to the potato yields after each of the leys. Maximum yields and maximum economic yields and their associated N dressings were then estimated. Maximum economic yields of wheat in 1987 ranged from 811 to 914 t/ha grain and the fertilizer N needed declined from 174 kg/ha after the one year ley to 48 kg/ha after the six year ley. For potatoes in 1988, yields ranged from 63 to 71 t/ha tubers but the N required (137–150 kg/ha) varied little with ley age. For winter wheat, in 1989 yields ranged from only 5·51 to 6·99 t/ha grain, because of drought but, as with the potatoes, the N required (203–218 kg/ha) varied little. For each crop the six individual N response curves could be shifted to bring them into coincidence, and the benefits of the ley estimated in terms of a quantity of fertilizer N applied in spring (horizontal shift) and effects other than spring N (vertical shift). The spring N effects relative to the one year ley varied with ley age; for the first wheat the range was from 6 to 126 kg N/ha for the two to six year leys respectively. Spring N effects were negligible, however, for potatoes (average 6 kg/ha) and also for wheat in the third year (6 kg/ha). Benefits other than those which could be ascribed to spring N increased yield of the first wheat, on average, by 0·94 t/ha grain for the two to five year leys; for potatoes they ranged from 3·5 to 8·1 t/ha tubers for the three to six year leys; for the third crop wheat they ranged from 0·86 to 1·49 t/ha grain for the three to six year leys.On average, the first wheat recovered only 34% of the applied fertilizer N whilst potatoes and the following wheat recovered 55 and 56% respectively. There was a benefit from the longer leys which affected the efficiency with which fertilizer N was used.Increasing ley age up to five years increased total soil carbon by a maximum of 0·17%C; 18% of the carbon content of the soil in the one year ley plots. This small increase in soil organic matter provided up to 230 kg/ha mineral N in the first autumn after ploughing. Between 17 October 1986 and 27 April 1987 the average loss of NO3-N from soils following three to six year leys was equivalent to 202 kg N/ha, whilst the average uptake of N by 11 May in the above-ground wheat was only 88 kg/ha; the net loss was 114 kg N/ha. A computer simulation, which included mineralization of organic N during this period together with N uptake and nitrate leaching losses, computed a loss of 250 kg N/ha following the six year ley, and this would have given 400 mg NO3/1 in the 275 mm through drainage that winter.

Description: SummaryDry weight, nutrient content and other properties of winter wheat were measured from anthesis to maturity between 1969 and 1984. From 1969 to 1978 the cultivar Capelle- Desprez was grown either as a first wheat, in the rotation potatoes, beans, wheat, or as a second wheat, in the rotation fallow, wheat, wheat. From 1979 to 1984 the cv. Flanders was grown in the rotation fallow, potatoes, wheat and in this period the wheat was given fungicide sprays. Grain yield of Cappelle-Desprez grown as a first wheat was greater with 96 than with 144 kg N/ha in spring. First wheats yielded much more than second wheats with 96, but not with 144 kg N/ha. Second wheats had more eyespot and take-all, but less mildew, than first wheats. Mildew was more severe with the larger amount of N. Grain yield of Flanders as a first wheat was greater than that of Cappelle-Desprez. Yield of Flanders was greater with 144 than with 96 kg N/ha and it was greater still on plots given 96 kg Nha plus 35 t/ha farmyard manure. Other properties in addition to grain yield were changed by cultivar, rotation and manuring.Examination of the variation between years showed relationships among properties and between some of them and grain yield. Many of the relationships were independent of cultivar or husbandry. Relationships between weather factors and some properties, but not grain yield, were detected. Grain yield of first wheats was closely related to number of grains/m2, but the relative importance of number of ears/m2 and number of grains per ear varied from year to year. Yield was positively related to dry weight per grain in Flanders, but negatively in Cappelle-Desprez. The weight of straw was usually less than that of the total above-ground crop at anthesis, but varied between years in a similar manner. The amount of N in grain plus straw was generally well related to the amount of N in the wheat at anthesis, although the changes in N content after anthesis ranged from a loss of 9 kg/ha to a gain of 51 kg/ha. The uptake of N, P and K was more closely related to dry weight than to nutrient concentration.Variation between years in the proportion in the ear of 14C supplied to the flag leaf was similar to that of 14C supplied to the next lower leaf, but was different for 14C supplied before and after anthesis, and did not relate to other properties.Date of anthesis ranged from 7 June to 5 July. A model incorporating responses to photoperiod, vernalization and temperature accounted for 78% of the variance in date of anthesis. The duration of the period from anthesis to leaf senescence ranged from 33 to 60 days and was linearly related to mean temperature above a base of 7·5 °C. Dry weight per grain was negatively correlated with mean temperature between anthesis and leaf senescence; a relationship including an adjustment for number of grains/m2 fitted both cultivars.The amount of N in grain plus straw and percentage of N in grain dry matter were decreased by increased rainfall during the 3-week period following the application of N fertilizer in spring. An additional 10 mm of rain decreased N uptake by 2–8 kg/ha and N percentage by 0·055. N uptake in grain plus straw decreased with progressively later sowing. Grain N% was positively correlated with temperature and with radiation during parts of the period of grain growth, but only 10% of the variance was accounted for by the combined effects.

Description: Nitrate loss in drainwater and cultivated layer flow was measured over 5 years on two pairs of hydrologically isolated plots, one pair with cereal straw incorporated for 4 years and burnt in the fifth, and the other with straw burnt in all 5 years. Although straw incorporation decreased nitrate leaching and probably decreased net mineralization of soil organic matter in the first winter, these effects were apparently diminished or even reversed in later winters, and the straw had no benefit on cereal yields or N-uptakes. The results suggest that the present practice on UK farms of regularly incorporating cereal straw is unlikely to decrease nitrate losses and in the long term may increase them, especially on clay soils and in wet winters after long dry periods. On clay soils it is also unlikely to increase crop yields in the short or medium term.