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Kvävetillgång i odlade mulljordar i Kvismardalen i Närke

Lindén, Börje (2015). Kvävetillgång i odlade mulljordar i Kvismardalen i Närke. Uppsala: (NL, NJ) > Dept. of Soil and Environment
(S) > Dept. of Soil and Environment
, Sveriges lantbruksuniversitet. Rapport (Sveriges lantbruksuniversitet, Institutionen för mark och miljö) ; 16
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Abstract

År 1878-88 sänktes sjöarna Kvismaren och Hjälmaren i Närke.
Härigenom kunde betydligt mer än 10 000 ha åkermark nyodlas. I föreliggande rapport redovisas fältförsök 1986-88 på kärrtorvmulljordar i området:

1) nio ettåriga försök med stigande mängder mineralgödselkväve(0, 30, 60, 90 och 120 kg N/ha) till vårkorn

2) sju ettåriga observationsförsök (”0N-rutor”) med vårkorn utan tillförsel av mineralgödselkväve.

Mängderna mineralkväve (ammonium- och nitratkväve) i jorden
bestämdes skiktvis (0-30, 30-60 och 60- 90 cm) under olika årstider. För att beskriva den mängd kväve från marken som grödorna kunde utnyttja under växtsäsongen (utnyttjbart jordkväve) bestämdes växternas kväveinnehåll vid
kväveupptagningens avslutning på sensommaren i behandlingarna utan kvävegödsling.

I medeltal fastställdes 166 kg utnyttjbart jordkväve per ha (variationsbredd: 78-274 kg/ha), ). I fastmarksjordar brukar det finnas i storleken 60-80 kg N/ha. Det fanns
inget tydligt samband mellan utnyttjbart jordkväve och mulljordsdjup (R2= 0,30) eller mullhalt
inom 30 cm djup (R2= 0,11). Tillgången på utnyttjbart jordkväve varierade betydligt mellan åren: 195, 230 och 113 kg N/ha 1986, 1987 respektive 1988. Mineralkvävet i marken uppvisade ett cykliskt årsförlopp, med 1) de minsta mängderna när grödornas kväveupptagning avslutades, 2) vanligen mycket stora anhopningar av mineraliserat kväve på hösten och även under vintern och 3) de största förråden på våren efter en kall vinter med långvarig tjäle
(1986-87). Under den milda vintern 1987-88 minskade däremot
mineralkvävet påtagligt fram till våren, vilket bidrog till att ökakvävegödslingsbehovet under den efterföljande växtsäsongen.

Med prisnivåer för 2013 uppgickden ekonomiskt optimala kväve
gödslingen till 33 kg N/ha (variationsbredd: 0-120 kg). Det fastställdes ett starkt samband mellan ekonomiskt optimal kvävegödsling till kornet och mineralkväve på våren eller utnyttjbart jordkväve. För mineralkväve erhölls R2= 0,84 och utnyttjbart jordkväve R2= 0,70. Den faktiska mängden utnyttjbart jordkväve kan
dock bara fastställas i efterhand i praktiken. För gödslingsprognoser måste kvävetillgången kunna förutsägas. De stora förråden av mineralkväve tidigt på våren (i medeltal 144 kg N/ha) tyder på att bestämning av detta kväve skulle kunna användas för att förbättra
precisionen vid kvävegödsling på mulljordar under det aktuella året. Problem med sådana gödslingsråd uppstår emellertid, om förluster av kväve sker genom nederbörd efter jordprovtagningen. För att styra kvävegödslingen, oavsett jordslag, har det istället föreslagits icke kvävegödslade smårutor (0N-rutor) inom fältet ifråga med
årliga provtagningar av grödan för bestämning av dess kväveupptag och utnyttja medeltal eller trend för detta som grund för efterföljande års gödsling. I försöken blev dock variationerna i utnyttjbart jordkväve mellan åren alltför stora för säkra gödslingsråd baserade
på medeltal för tidigare år. För tillförlitligare bedömningar av gödslingsbehovet bör det vara säkrare med metoder som belyser grödornas kvävestatus under den på
gående växtsäsongen, såsom reflektansmätning i växande gröda.

Vid optimal gödsling översteg i allmänhet inte det outnyttjade mineralkvävet vid avslutad kväveupptagning mängderna i icke kvävegödslade led med mer än några få kg N/ha. Destora kväve mineralieringstillskotten under hösten måste ha ökat risken för kväveförluster under vinterhalvåret
betydligt mer. Detta bör motverkas genom odling av fånggrödor och genom att skjuta upp jordbearbetningen till våren.

Authors/Creators:Lindén, Börje
Title:Kvävetillgång i odlade mulljordar i Kvismardalen i Närke
Alternative abstract:
LanguageAbstract
UNSPECIFIED

During the 19th and the early 20th centuries, huge areas of organic soils were reclaimed in Sweden through drainage of peatlands and lowering of lakes and streams. The acreage of reclaimed peat- and wetlands reached about 700 000 ha in the mid-1940s. Later, however, the agricultural use of organic soils has declined. The largest lowering of lakes for reclamation concerned the lakes Mosjön, Kvismaren and Hjälmaren in the province of Närke in central Sweden. Through the lowering of Kvismaren and Hjälmaren (1878-88), more than 10 000 ha of cultivated soils were gained in the Kvismar Valley. During the period 1886-1939, the reclamation of organic soils in Sweden gave rise to extensive research on the soil fertility status of these soils and, e.g., the need for nitrogen fertilisation. Later, the interest in investigating plant nutrient conditions in organic soils, such as crop demand for fertiliser nitrogen, generally declined. Starting in the 1970s, attention was increasingly paid in Sweden to the risk of enhanced nitrogen leaching in cultivated soils due to nitrogen fertilisation. The County Administrative Board in Örebro observed increased eutrophication of lakes and streams in the province of Närke, including Lake Hjälmaren. During the 1980s, the extent to which this eutrophication could be attributed to the cultivated organic soils and the occurrence of nitrogen fertilisation on these soils was discussed.

In the present report, nitrogen fertilisation trials in 1986-88 on organic soils in the Kvismar Valley are described. The investigations were performed in order to study nitrogen release, crop use of this nitrogen and the demand for nitrogen fertilisation, as well as to describe the risks of nitrogen leaching and the reason for such losses. According to the farmers involved, nitrogen fertilisers were used rather frequently on these soils, about 60 kg N/ha as regards spring cereals, although nitrogen mineralisation generally should have been very large.

Two types of field experiments were carried out in 1986-88: 1) nine annual trials with increasing rates of fertiliser nitrogen to spring barley (series L3-2166) and 2) seven annual observation plots (“0N plots”) with spring barley without application of fertiliser nitrogen (series L3-2161), Table 1 and Figure 1. The experiments were performed on cultivated fen peat soils with varying depths of the organic soil layer (25-90 cm, Table 1) and varying soil organic matter (SOM) contents (Tables 2, 3 and 6). In the nitrogen fertilisation experiments, having three blocks, nitro chalk (containing ammonium nitrate) was placed at sowing in amounts corresponding to 0, 30, 60, 90 and 120 kg N/ha. The 0N plots con-sisted of one single area, 10*20 m in size. Soil mineral nitrogen (ammonium and nitrate nitrogen) was determined in different seasons. For this, soil samples were taken from the 0-30, 30-60 and 60-90 cm soil layers in all experiments. The nitrogen contents of the crops were investigated by sampling the above-ground plant material at dough or yellow ripeness, i.e. when nitrogen uptake was ceasing, within the 0N plots and in the treatment without fertiliser nitrogen (A) in the nitrogen fertilisation trials. The nitrogen uptake, including the estimated nitrogen content of the roots, in these treatments was used to quantify the supply of plant-available soil nitrogen during the growing season. The 0N plots and the treatment without nitrogen application in the fertilisation trials were also used for calculations of nitrogen mineralisation during the growing season using the following formula: (crop uptake of nitrogen at dough or yellow ripeness) + (soil mineral nitrogen at the same time) – (soil mineral nitrogen in early spring), Lindén et al. (1992a). Five annual 0N plots were laid out during the first year (1986). At one of these sites, a new 0N plot was established in 1987 and 1988. Thus the number of 0N plots was seven. The nitrogen fertilisation trials were performed annually on three fields (totally 9 trials), but they were moved some¬what within the site in each year.

In all experiments (n = 16) the supply of plant-available soil nitrogen during the growing sea¬son averaged 166 kg N/ha (range: 78-274 kg), Table 9. In mineral soils with normal SOM contents, i.e. about 2-5% SOM (Lindén et al. 1992b and 1993a; Delin, 2005; Engström, 2010), generally about 60-80 kg N/ha is found under Swedish conditions (Lindén, 1987; Lindén et al., 1992a-b). The amounts of plant-available soil nitrogen varied considerably between years (Table 9), obviously due to differences in the weather conditions. Thus, the barley crops in the four 3-year trials in 1986, 1987 and 1988 took up, on average, 195, 230 and 113 kg/ha of plant-available soil nitrogen, respectively.

The amounts of plant-available soil nitrogen could only to some extent (R2 = 0.30) be related to the depth of the organic soil layer (within 0-90 cm), and the effect of varying SOM contents within 0-30 cm on the supply of plant-available nitrogen was quite insignificant (R2 = 0.11). These results could partly be explained by the great variations between years in plant-available nitrogen. Thus it does not seem to be feasible to use determinations of SOM in the topsoil or the depth of the organic soil layer for predicting the de-mand for fertiliser nitrogen in this type of soils in a certain year.

Soil mineral nitrogen (0-90 cm) annually showed a cyclic time course with 1) the smallest amounts when crop uptake of nitrogen ceased in late summer, 2) large accumulations of mineralised nitrogen in the soil in the autumn, and even in the winter, and 3) the largest storages in spring (April) after a cold winter (1986-87) with a long period of ground frost (Tables 10 and 13, Figure 3). The winter in 1987-88, following an autumn with large precipitation, was mild. The ground was just frozen shortly and superficially in the winter. In this case, soil mineral nitrogen largely decreased from early autumn until early spring.

Despite these variations, considerably more mineral nitrogen was found in the investigated organic soils during all seasons than in mineral soils with normal SOM contents (about 2-5%, see above), obviously due to larger mineralisation capacity. In the organic soils, the residual amount of soil mineral nitrogen averages 53 kg N/ha in late summer in 1986, compared with normally 15-35 kg in mineral soils without nitrogen fertilisation. Until late autumn, the average amount increased to 136 kg, and to 217 kg in April 1987. Following the mild winter in 1987-88, however, only 73 kg N/ha remained in early spring. In Swedish mineral soils with normal SOM contents, however, soil mineral nitrogen (within 0-90 cm) in early spring generally does not exceed 30-50 kg N/ha after cereal crops (Mattsson & Anderson, 1984; Lindén, 1987; Lindén et al., 1992b).

The calculations of nitrogen mineralisation during the growing sea-son seemed to unreliable, frequently showing values of the same size as in mineral soils (Lindén, 1987; Delin 2005; Engström, 2010). Moreover, no relationship between nitrogen mineralisation and plant-available soil nitrogen was found (R2 = 0.01). The reason may be nitrogen losses from the investi¬gated soil profiles in spring and/or during the subsequent growing season, affecting the calcu-lations.

Economically optimum nitrogen fertilisation in the annual trials with increasing rates of fertiliser nitrogen (n = 9) was calculated according to prices of fertiliser nitrogen and barley ker¬nel in 1988 and 2013, corresponding to price quotients for fertiliser/kernel = 5.50 and 9.00, respectively (Figure 6). With the price levels of 2013, optimum nitrogen fertilisation averaged 33 kg N/ha (range: 0-120 kg).Very close relationships were obtained between optimum fertilisation and plant-available soil nitrogen during the growing season or soil mineral nitrogen (0-90 cm) in early spring. With the two price levels used (for 1988 and 2013), R2 values as high as 0.86 and 0.70, respectively, were obtained for plant-available soil nitrogen and R2 = 0.89 and 0.84, respectively, for soil mineral nitrogen in spring (Figure 7).

As an average of all sites studied in the Kvismar Valley and all years (n = 16) as much as 144 kg/ha of soil mineral nitrogen (0-90 cm soil depth) was found in spring (range: 35-300 kg). This gener-ally large supply, the large variation and the close relationship with optimum nitrogen fertilisation indicate that determinations of mineral nitrogen in organic soils in early spring could be used to im-prove the accuracy of nitrogen fertilisation. However, evaluation in practical agriculture showed that the recommendations were not reliable enough, probably due to nitrogen losses after soil sampling in spring (Figure 3).

For more precise nitrogen recommendations, the use of 0N plots has been proposed in practical agriculture in Sweden. Through crop sampling within 0N plots in the field in question shortly before maturity and determinations of crop uptake of nitrogen in such plots, average data would be gained after some years that could be used for adjusting nitrogen application in a subsequent year. In the four organic soils studied in 1986-88 in the Kvismar Valley, however, the variation in plant-available soil nitrogen between the years was too large (Tables 9 and 12) for a reliable use of 0N plots as a basis of nitrogen recommendations.

None of the discussed methods of describing soil nitrogen supply to crops seems to be pos¬sible to use for fertilisation recommendations on organic soils, as the variations in soil nitro¬gen conditions and plant growth during the growing season cannot be foreseen. For more reliable estimations of the demand for fertiliser nitrogen, other methods have been proposed that can describe crop nitrogen status during the current growing season. For instance, nitrogen fertilisation rates may be regulated by means of reflectance measurements at the time of fertilisation in annual 0N plots or in already nitrogen-fertilised crop, using e.g. the Yara N sensor. The use of this sensor seems to be rather advantageous under Swedish conditions (Gruvaeus, 2008, Frostgård, 2013). Therefore, the possibility of using this method should also be investigated on organic soils.

The unused amounts of soil mineral nitrogen at dough or yellow ripeness following optimum nitrogen fertilisation generally did not exceed the residual amounts in treatment A (without nitrogen fertilisation) with more than a few kg N/ha. The largest amounts of unused mineral nitrogen were mainly found following clearly overoptimum nitrogen rates on soils with large supplies of plant-available soil nitrogen (Figure 8). The optimum rates of fertiliser nitrogen were somewhat lower at the price level for 2013 than for 1988 (Figures 6 and 8), but with the prices for 2013 the amounts of unused mineral nitrogen decreased only by 1 or 2 kg N/ha, thus with insignificant effects on the risks for increased nitrogen leaching in this respect. On the other hand, the large accumulation of mineralised nitrogen in the organic soils in autumn should have enhanced the risk of nitrogen losses considerably during the winter period. Therefore it should be especially important to counteract this accumulation. For this, catch crops ought to be cultivated. Moreover, nitrogen mineralisation should not be stimulated through soil tillage during autumn (Stenberg et al., 1999). Instead, tillage should be post¬poned until spring.

The winters in 1985-86 and 1986-87 were cold (Table 8), with a long period of ground frost in the Kvismar Valley. After these winters very large amounts of overwintering soil mineral nitrogen were found in spring (see above). During the wet autumn of 1987 and the mild winter in 1987-88, mainly with unfrozen soil, large nitro-gen losses obviously occurred, as comparatively small amounts of soil mineral nitrogen remained in the following spring. This reduced the supply of plant-available soil nitrogen. Consequently, the optimum demand for fertiliser nitrogen became larger than during both previous years. Thus, more precipitation during cold seasons and milder winters due to climate change may enhance the demand for fertiliser nitrogen on cultivated organic soils in Sweden.

Series/Journal:Rapport (Sveriges lantbruksuniversitet, Institutionen för mark och miljö) (11698476)
Year of publishing :2015
Depositing date:January 2015
Number:16
Number of Pages:76
Place of Publication:Uppsala
Publisher:Institutionen för mark och miljö, Sveriges lantbruksuniversitet
ISBN for electronic version:978-91-576-9277-1
Language:Swedish
Publication Type:Report
Full Text Status:Public
Agris subject categories.:F Plant production > F04 Fertilizing
P Natural resources > P35 Soil fertility
Subjects:(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Soil Science
Agrovoc terms:organic soils, carbon, nitrogen, leaching, nitrogen fertilizers, soil testing, analytical methods, sweden
Keywords:kväveutlakning, kvävegödsling, organogena jordar
URN:NBN:urn:nbn:se:slu:epsilon-e-2310
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-2310
ID Code:11747
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
S - Faculty of Forest Sciences
Department:(NL, NJ) > Dept. of Soil and Environment
(S) > Dept. of Soil and Environment
Deposited By: Professor Anna Mårtensson
Deposited On:19 Jan 2015 12:50
Metadata Last Modified:14 Dec 2015 20:30

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