Crop Production in the East of Scotland - SASA

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Climate2. CLIMATEshadow effect). A “blocking” anticycloneover Scandinavia or the Bay of Biscay canpush the depressions further west or north,resulting in generally drier, morecontinental weather. In winter, climaticdifferences tend to run east-west whereasin summer they run north-south. East-westdifferences also arise from the proximity tothe coast, on the one hand, and mountainson the other.August cereal harvest under optimal conditions,near North Berwick, East LothianThe climate of the East of Scotland istemperate without extremes of temperatureor rainfall but, although meteorologicalcatastrophes are rare, the success ofagriculture is dominated by weather. Effectscan be direct, such as the destructiveinfluence of freezing temperatures, orindirect, through the vulnerability of wetland to compaction by heavy machinery. Itis common for crop yield to be influencedby interactions between soil type and waterrelations, or temperature.The weather in Scotland is dominated bythe particular air mass passing over, since itlies close to the track of depressions fromthe North Atlantic. The prevailing winds arepredominantly from the south west,bringing humid air, which depositsprecipitation when forced to rise over theWestern and Central Highlands, and theSouthern Uplands. By the time that suchairflows reach the East of Scotland, muchof the moisture content has been lost (rainFrancis (1981) classified the agriculturalareas of Scotland using mean annualrainfall, as soil water rather than growingseason length (based on temperature) isthe dominant limiting factor for cropping inScotland. He compiled tables of manymeteorological and agriculturally-relevantattributes for each area (Table 2.1).Although his calculations were based ondata from the period 1941-1970, currentfigures are broadly similar. However,variation from season to season is usuallymore important than long term averages:when decisions are being made aboutcapital investment in plant and machinery, abalance must be struck between the needsof the “average” season and the risksassociated with more extreme events; inthe shorter term, decisions on the rate andtiming of inputs must be made in ignoranceof the actual conditions to be encounteredby the crops.For land capability purposes (see Chapter3), Scotland has been mapped using themedian value of the highest potential soilwater deficit and the lower quartile value ofaccumulated day-degrees above 0°C for thefirst six months of the year (Bibby et al.,1991; note that physiologists prefer to usedegree days). The former is really an indexof how wet rather than how dry the site iswhereas the latter determines which cropscan be fitted into the growing season17
Crop Production in the East of ScotlandTable 2.1Selected climatic data for regions in the East of ScotlandBorders Lothian Fife Angus & NE InvernessPerthshire Scotland & E RossGrowing season (d) 215 225 225 220 210 215Mean winter temperature (°C) 5.1 4.3 5.0 4.5 3.7 4.7Mean summer temperature (°C) 12.0 11.2 12.0 11.7 10.7 11.4Last spring frost a Apr III Apr II Apr II Apr II May I Apr IIIAnnual rainfall (mm) 813 675 825 912 888 803Mean PET b (mm) 465 500 473 440 415 443Access period c (d) 203 240 205 182 170 198First soil moisture deficit Mar I Mar I Mar I Mar I Mar II Mar IReturn to field capacity Oct II Nov II Oct II Oct II Oct II Oct IIIHighest summer SMD d (mm) 83 100 83 72 68 78Excess winter rainfall (mm) e 310 195 320 395 368 303Source: Francis (1981);a I = first 10 days of the month etc.;b PET=potential evapotranspiration;c access for farm machinery;d SMD=soil moisture deficit;e rainfall which must be removed by drainage (i.e.allowing for soil water recharge and evaporation)(based on temperature). Winter wheat,barley, oilseed rape and potatoes aregenerally well-adapted to the climate of theEast of Scotland, with pasture grassesthriving in the wetter parts. Adaptedspecies of coniferous and broadleaf treesgrow well, with high yield classes infavourable locations.TemperatureAnalysis of long term records shows thatair temperatures below -15ºC or above 30ºCare extremely rare. The mean annual airtemperature, as measured in standardmeteorological screens, is about 8.5ºC forthe whole area, with lower temperaturesinland and towards the altitudinal limit ofcultivation. The range from the coldest(January) to the warmest (July) month istypically also 8.5ºC, which is slightlygreater than the mean diurnal temperaturerange of 7ºC. As the air temperatureincreases on average by only 0.33ºC perday during February, March and April, latefrosts and reversions to winter weather arecommon in early spring. In Table 2.1 themean date of the last spring frost is givenin months and dekads (ten day periods).The inter-quartile range is about fourweeks, showing the considerable variationamong growing seasons.Temperatures are too low to allowsuccessful commercial growing of maize,sunflower or soya, although in recent yearsforage maize has been grown in the slightlywarmer South-West of Scotland. For welladaptedspecies (wheat, barley, potatoes,grassland), temperatures are generally suboptimalfor growth rate (i.e.
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Page 6 and 7: PrefacePrefaceIn April 2000, I laun
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Crop Production in the East of Scotland - SASA

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