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Kvävetillgång och växtodling på en kärrtorvjord ovanpå lergyttja i Uppland

en fallstudie

Lindén, Börje (2013). Kvävetillgång och växtodling på en kärrtorvjord ovanpå lergyttja i Uppland. Uppsala, Sverige: (NL, NJ) > Dept. of Soil and Environment
(S) > Dept. of Soil and Environment
, Sveriges lantbruksuniversitet. Rapport (Sveriges lantbruksuniversitet, Institutionen för mark och miljö) ; 12
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Abstract

För att belysa grödornas tillgång på växttillgängligt markkväve i en organogen jord valdes ett åkerskifte med sådan jord ut för studier 1987-88 på gården Finnsholmen invid Vretaån i nordvästra Uppland. Ån sänktes 1896-98, vilket torrlade 3300 ha mossar och översvämmade arealer i Huddunge, Nora, Harbo och Östervåla socknar. Genom åsänkningen kunde det nämnda fältet odlas upp. Det hade brukats i drygt 70 år, när denna undersökning genomför-des, och nu (2013) i omkring 100 år. I en litteraturöversikt som bakgrund till studier av jord-måns-, växtodlings- och kväveförhållandena på platsen beskrivs den omfattande uppodlingen av sankmarker samt sänkta sjöar och vattendrag i Sverige under 1800-talet och i början av 1900-talet. Här kan sänkningen av Vretaån ses som ett exempel. Svenska Mosskulturför-eningen (1886-1939) bedrev en omfattande försöksverksamhet på mulljordar. Studierna visade bl.a. att mosstorvjordar var kvävefattiga, medan kärrtorvjordar oftast inte behövde kvävegödslas. Marken inom fältet på Finnsholmen tillhör den senare kategorin.

Undersökningarna bedrevs inom en representativ observationsyta (48*100 m) inom skiftet. Vårkorn odlades på fältet 1987 och matpotatis 1988, båda åren utan kvävegödsling. Kväve-förhållandena inom observationsytan undersöktes främst genom bestämning av de årstidsvisa variationerna i mängderna mineralkväve (ammonium- och nitratkväve) i markprofilen (0-30, 30-60 och 60-90 cm) samt genom bestämning av totalkväveinnehållet bl.a. i skördarna.

Inom 0-30 cm djup hade jorden inom observationsytan 1987-88 en mullhalt på drygt 60 % och ett pH-värde på 5,3. Under plogdjup och ned till 35-40 cm innehöll marken högförmult-nad kärrtorv och därunder lergyttja. Inom 30-60 och 60-90 cm djup var pH-värdena så pass låga som 4,2 respektive 3,5. Rötterna nådde huvudsakligen bara ned i den översta decimetern av lergyttjan. Denna kännetecknades av permanent sprickbildning. Härigenom blev jorden självdränerande. Kornets avkastning (biologisk skörd) 1987 uppgick till närmare 5900 kg kärna per ha inom observationsytan. Potatisen år 1988 gav en knölskörd på 31 ton per ha. Skördarna av både kornet och potatisen var högre än medelavkastningen av dessa grödor i Uppsala län och angränsande län vid denna tid enligt SCB:s statistik.

Jämfört med fastmarksjordar fanns anmärkningsvärt mycket ammoniumkväve i alven (sär¬skilt på 60-90 cm djup), troligen till följd av de låga pH-värdena. Inom 0-90 cm fanns 151 kg/ha som medeltal för alla provtagningstillfällen. Även mängden nitratkväve var jämförel¬sevis stor, i genomsnitt 131 kg N/ha inom 0-90 cm djup. Under somrarna minskade mineral¬kvävet inom 0-30 cm genom grödornas kväveupptag. I alven förblev dock detta kväve i hög grad outnyttjat. Under höstarna tilltog mängderna genom fortsatt kvävemineralisering. Dessa förhållanden kan ha medfört ökad kväveutlakning och tyder på behov av fånggrödor. Vidare bör jordbearbetningen skjutas upp till våren för att inte stimulera kvävemineraliseringen.

År 1987, då korn odlades, erhölls ett nettomineraliseringstillskott av kväve på 184 kg/ha från den 12 maj till den 4 november. Detta korn beräknades ha tagit upp 195 kg jordkväve per ha (inkl. en del övervintrande mineralkväve), och potatisen 1988 omkring 100 kg N/ha. Denna stora skillnad i mängderna utnyttjat jordkväve väcker frågan, om inte kvävemineraliseringen i organogena jordar kan variera kraftigt mellan åren. Både kornet och potatisen gav dock höga skördar utan tillförsel av gödselkväve. Beräknat för kvävebehovet för en kornskörd på 5000 kg/ha och en potatisskörd motsvarande 30 ton/ha innebär markens kväveleverans här en besparing på ca 100 kg mineralgödselkväve per ha och år jämfört med normala fastmarks-jordar, till ett värde av ca 1100 kr per ha och år enligt gödselpriser 2012-2013.

Authors/Creators:Lindén, Börje
Title:Kvävetillgång och växtodling på en kärrtorvjord ovanpå lergyttja i Uppland
Subtitle:en fallstudie
Alternative abstract:
LanguageAbstract
UNSPECIFIED

During the 19th and the early 20th centuries, huge areas of organic soils (moss peat, fen peat and gyttja soils) were reclaimed in Sweden through drainage of peatlands and lowering of lakes and streams. This gave rise to extensive research on the soil fertility conditions and the need for fertilisation of such soils. Later, the interest in investigating plant nutrient conditions in organic soils, e.g. crop demand of fertiliser nitrogen, generally declined. Thus only a few investigations of soil nitrogen dynamics and crop demand for nitrogen in organic soils seem to have been carried out in Sweden during recent decades. In order to describe the supply of plant-available soil nitrogen and other crop production conditions on an organic soil, a field on the Finnsholmen farm in the north-west part of the province of Uppland in central Sweden was chosen for investigations in 1987-88. Here a fen peat overlying a clay gyttja soil had been drained and reclaimed after lowering the neighbouring river Vretaån in 1896-98.

The investigations in this case study were performed within a chosen observation plot (48*100 m) on the field in question. Spring barley was grown on the field in 1987 and potatoes in 1988, without nitrogen fertilisation in both years. As a background to the studies, the large-scale reclamation in order to increase the agricultural acreage of Sweden through drainage of wetlands and lowering lakes and streams during the 19th and early 20th centuries is briefly described in a literature review. Here, the drainage and reclamation of wetlands along the river Vretaån serves as an example.

Soil nitrogen conditions within the observation plot were investigated mainly through determination of the seasonal variations in mineral nitrogen (ammonium and nitrate nitrogen) in the soil profile. For this, soil samples from the 0-30, 30-60 and 60-90 cm soil layers were taken repeatedly from May 1987 until November 1988. The samples were also used for analyses of soil composition and chemical properties. During the barley year (1987), the crop was sampled at different development stages until maturity in order to describe plant growth, nitrogen uptake and grain yield. The potato crop in 1988 was sampled only in September in order to determine the tuber yield and its nitrogen content. For determination of dry bulk density (volume weights), undisturbed soil samples were taken in 10-cm layers down to 90 cm. Soil pH was determined in deionised water. On the occasions of soil sampling, the properties of the soil profile were also examined visually.

Due to a rapid increase of the population in Sweden during the 19th century and insufficient food supply, more arable land and increased agricultural production were needed. The total agricultural acreage in Sweden increased from less than 900 000 ha in the beginning of the 19th century to almost 3 800 000 ha about 1920. This includes ca. 600 000 ha of reclaimed peat- and wetlands until that time, reaching about 700 000 ha in the mid-1940s. Later, the acreage of cultivated organic soils has declined and has been estimated to less than 268 000 ha in 2008, partly due to deteriorated drainage caused by decomposition of the soil organic matter and subsequent subsidence.

In the province of Uppland, extensive drainage projects have been carried out, e.g. the lowering of Lake Tämnaren and tributary streams, where large areas of peat- and wetland and former lake bottoms have been reclaimed. From the west, the river Vretaån falls into Lake Tämnaren. This stream was excavated and lowered in 1896-98 (Figures 2-3). Through this, peatland and flooded areas corresponding to about 3,300 ha were drained. Two further excavations were performed, the last one in 1959. Within about 17 years after the excavation in 1896-98, the farmers concerned obviously had reclaimed the gained acreage. This implies that the organic soil within the field at Finnsholmen had been cultivated for slightly more than 70 years, when the reported investigation was performed in 1987-88, and now (in 2013) for about 100 years. In the 1940s, phosphorus and potassium fertilisers were introduced in the crop cultivation of the farm. The field studied was limed in 1982-83. Then a 3-year crop rotation was introduced, with potatoes, spring wheat and spring barley. The potato crop was fertilised with large amounts of phosphorus and potassium, partly in order to improve soil fertility in the long run. According to the experience of the farmer, the cultivated crops generally had no need for fertiliser nitrogen due to the occurrence of lodging and deteriorated potato quality, obviously caused by a surplus of plant-available nitrogen.

Within 0-30 cm depth, the soil in the observation plot in 1987-88 contained about 60 % organic matter and had a pH value of 5.3. Below ploughing depth and down to 35-40 cm, the soil contained a highly humified fen peat and beneath this a clay gyttja soil. The soil in the 30-60 and 60-90 cm layers had 16 and 9 % organic matter and pH values as low as 4.2 and 3.5, respectively. Root depth was mainly restricted to the uppermost decimetre of the clay gyttja. There, and within the deepest centimetres of the peat, bush-like root concentrations were observed. The limited root depth was probably due to the low soil pH. In November 2012, on average only 30 cm (range: 22-35 cm, n = 11) of the topsoil and underlying peat layer remained above the gyttja soil. This limited, uppermost layer suggests that future soil subsidence should be moderate. The studied gyttja soil layer was characterised by permanent cracks, obviously permitting sufficient drainage of the soil profile. Drainage is also adequate at this site as the soil surface is situated more than 2 m above the neighbouring river Vretaån. Whereas huge areas of agricultural organic soils in Sweden only have been used for a century or much less due to subsidence and hence deteriorated drainage, this implies that there are prerequisites of a more persistent crop production on this field at Finnsholmen.

The grain yield of the barley in 1987, determined by clipping plants randomly within subplots, amounted to almost 5,900 kg/ha. In the potato year (1988), the tuber yield was 31 tonnes/ha. Both yields were larger than average yields in the region at that time according to official statistics.

The amount of ammonium nitrogen within the 0-30 cm soil layer was 7 kg/ha as a mean of 12 sampling occasions. This agrees with normal values for cultivated mineral soils in Sweden. In the 30-60 cm layer somewhat more ammonium nitrogen was found than normal. Within 60-90 cm soil depth remarkably large amounts were present, on average 129 kg/ha, whereas the corresponding layer in Swedish mineral soils normally contain only a few kg/ha. The reason probably is that the low pH values hindered nitrification of ammonium formed through mineralisation. The amounts of nitrate nitrogen were also large compared to mineral soils, amounting to 131 kg N/ha, on average, within the 0-90 cm soil layer.

In the growing seasons of 1987 and 1988, soil mineral nitrogen decreased, obviously due to crop uptake of nitrogen. The 0-30 cm soil layer was almost “emptied” of nitrate nitrogen, until only 4-6 kg/ha remained during the growing season of barley and 14 kg/ha during cultivation of the potato crop. This is similar to the conditions in mineral soils in Sweden. To a smaller extent, crop uptake of nitrogen also seemed to reduce mineral nitrogen in the 30-60 cm layer, but obviously not within the 60-90 cm soil depth. The low pH values in the clay gyttja soil and hence a shallow root system should explain the generally insignificant use of nitrogen in the subsoil, compared to normal conditions in clay soils in Sweden. During the main part of both growing seasons, nitrogen uptake seemed to exceed nitrogen mineralisation in size. This implies that mineral nitrogen, overwintering in the soil profile and/or mineralised early in spring, also was used by the crops to some extent.

The reduction of the amounts of soil mineral nitrogen during both growing seasons continued until crop uptake of nitrogen ceased in August-September. In the following autumns, however, mineral nitrogen increased again, obviously due to continued mineralisation. The incomplete utilisation of mineral nitrogen within 30-90 cm soil depth in the summer and the accumulation of mineralised nitrogen in the autumn may have led to enhanced nitrogen leaching during the subsequent winters. Nevertheless, soil mineral nitrogen increased from November 1987 until mid-April 1988. This suggests limited nitrogen losses. However, the results indicate a need for catch crops on organic soils of this kind in order to reduce leachable nitrogen in the autumn. Moreover, soil tillage in the autumn stimulates nitrogen mineralisation and should therefore be postponed until the spring.

In 1987, nitrogen mineralisation amounted to 184 kg N/ha from 15 May until 4 November, as calculated on the basis of the nitrogen uptake by the spring barley and changes in soil mineral nitrogen during this period. Of this amount, 125 kg N/ha was released from spring until August, when the nitrogen uptake of the barley obviously was ceasing. This may be compared with mineral soils in Sweden with normal organic matter contents, in which nitrogen mineralisation from spring until the end of nitrogen uptake was found to be 40-50 kg N/ha, on average, according to cited investigations with cereals cultivated following cereals. The barley in 1987 took up 195 kg N/ha originating from the soil, and the estimated nitrogen uptake of the potato crop amounted to about 100 kg N/ha. This large difference between the two years gives rise to the question, whether nitrogen mineralisation and/or nitrogen losses during the growing season may vary considerably between years in organic soils.

Compared to common yield levels in the region, the yields of the barley and potato crops within the observation plot at Finnsholmen were high in spite of no nitrogen fertilisation. The barley in 1987 obviously did not need any fertiliser nitrogen as vigorous lodging occurred in that year. According to the farmer, the quality of the tuber yield frequently had been deteriorated in earlier years obviously due to too much plant-available soil nitrogen. As calculated for the nitrogen demand of spring barley yielding 5000 kg grain per ha and a potato crop producing 30 tonnes per ha, the supply of plant-available soil nitrogen implies a saving of 100 kg of fertiliser nitrogen per ha and year, compared with recommended fertilisation at the same yield levels on normal mineral soils. Considering fertiliser prices in 2012-13, this corresponds a cost reduction of about 1100 SEK per ha and year.

Series/Journal:Rapport (Sveriges lantbruksuniversitet, Institutionen för mark och miljö) (11698476)
Year of publishing :May 2013
Number:12
Number of Pages:40
Place of Publication:Uppsala, Sverige
Publisher:Institutionen för mark och miljö, Sveriges lantbruksuniversitet
ISBN for printed version:978-91-576-9144-6
Language:Swedish
Publication Type:Report
Full Text Status:Public
Agris subject categories.:P Natural resources > P30 Soil science and management
Subjects:(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Agricultural Science
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Soil Science
Keywords:Sankmarker, mineralkväve, kvävemineralisering, utlakningsrisk, gödselkvävebehov, uppodling, Peatlands, mineral nitrogen, risk of leaching, reclamation, nitrogen mineralisation, demand for fertiliser nitrogen
URN:NBN:urn:nbn:se:slu:epsilon-e-1466
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-1466
ID Code:10445
Department:(NL, NJ) > Dept. of Soil and Environment
(S) > Dept. of Soil and Environment
Deposited By: Anna Nyberg
Deposited On:20 May 2013 07:46
Metadata Last Modified:02 Dec 2014 11:01

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