Abstract
Nitrification and nitrate leaching have been suggested to be major causes of soil acidification. However, it is unknown whether these processes cause subsoil acidification. Soil column experiments examined the effect of the addition of Ca(NO3)2 or (NH4)2SO4 to the topsoil horizon on subsoil acidification under nodulated lupins ( Lupinus angustifolius L.) and subterranean clover ( Trifolium subterraneum L.). Nitrate leaching was achieved by adding excess water to the surface of the columns. Where basal nutrients were applied only to the top 10-cm layer, about 60–70% of the total root length of lupin and over 50% of subterranean clover were distributed in that layer. Plants grown without added nitrate for 105 days decreased soil pH at all layers but more significantly in the top 20 cm (by up to 0.7 units); the decrease in pH correlated well with increased root length density of both species ( r 2 = 0 .9 8 , n = 9). The addition of Ca(NO3)2 to the top 10-cm layer caused less acidification by about 0.1 pH units at all depths than the treatment without Ca(NO3)2 . Where basal nutrients were applied uniformly throughout the column, root length density of lupin and subterranean clover tended to increase with depth. The addition of (NH4)2SO4 in the top 10 cm significantly increased NO3– concentration in all layers but NH4+ was mainly retained in the top 30-cm layer. Lupin and subterranean clover grown without added NH4+ for 82 days decreased soil pH by 0.3 units at all depths. Compared with the plants receiving no (NH4)2SO 4 , lupin grown with (NH4)2SO4 at 0–10 cm depth in the column caused more acidification by 0.05–0.2 pH units in the top 10 cm but less acidification by 0.15–0.17 units at 10–40 cm depth in the column; subterranean clover grown with (NH4)2SO4 caused more acidification by 0.35–0.46 units in the top 10 cm and less acidification by 0.14–0.19 units in the 20–50 cm layer. The results suggest that the leaching of nitrate from topsoil is unlikely to cause subsoil acidification. In contrast, the uptake of nitrate by the roots reduces net acid production in subsoil layers.
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Claims 11
Claim · model-written summary
Lupin roots concentrated in the top soil layer.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“about 60–70% of the total root length of lupin”
Claim · model-written summary
Clover roots concentrated in the top soil layer.
- Taxon
- subterranean clover
Trifolium subterraneume0 - Outcome
- subterranean clovere0
- Value
- 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“over 50% of subterranean clover were distributed in that layer”
Claim · model-written summary
Plants without added nitrate lowered soil pH by up to 0.7 units, most strongly in the top 20 cm.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plants grown without added nitrate for 105 days decreased soil pH at all layers but more significantly in the top 20 cm (by up to 0.7 units)”
e1“under nodulated lupins ( Lupinus angustifolius L.) and subterranean clover ( Trifolium subterraneum L.)”
Claim · model-written summary
Soil pH decrease correlated with root length density.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the decrease in pH correlated well with increased root length density of both species ( r 2 = 0 .9 8 , n = 9)”
e1“lupins ( Lupinus angustifolius L.) and subterranean clover ( Trifolium subterraneum L.)”
Claim · model-written summary
Calcium nitrate addition caused about 0.1 pH units less acidification.
- Treatment
- Ca(NO3)2e0
- Outcome
- acidificatione0
- Direction
- lesse0
- Value
- 0.1 pH unitse0
- Comparator
- treatment without Ca(NO3)2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The addition of Ca(NO3)2 to the top 10-cm layer caused less acidification by about 0.1 pH units at all depths than the treatment without Ca(NO3)2”
e1“lupins ( Lupinus angustifolius L.) and subterranean clover ( Trifolium subterraneum L.)”
Claim · model-written summary
Ammonium sulfate increased nitrate concentration across layers.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The addition of (NH4)2SO4 in the top 10 cm significantly increased NO3– concentration in all layers”
e1“lupins ( Lupinus angustifolius L.) and subterranean clover ( Trifolium subterraneum L.)”
Claim · model-written summary
Without ammonium, plants lowered soil pH by 0.3 units.
- Taxon
- Lupin and subterranean clover
LupinusTrifolium subterraneume0 - Treatment
- without added NH4+e0
- Outcome
- soil pHe0
- Direction
- decreasede0
- Value
- 0.3 unitse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lupin and subterranean clover grown without added NH4+ for 82 days decreased soil pH by 0.3 units at all depths”
Claim · model-written summary
Ammonium sulfate caused greater topsoil acidification under lupin.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“lupin grown with (NH4)2SO4 at 0–10 cm depth in the column caused more acidification by 0.05–0.2 pH units in the top 10 cm”
Claim · model-written summary
Ammonium sulfate caused less subsoil acidification under lupin.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“less acidification by 0.15–0.17 units at 10–40 cm depth”
e1“lupin grown with (NH4)2SO4”
Claim · model-written summary
Ammonium sulfate caused greater topsoil acidification under clover.
- Taxon
- subterranean cloverTrifolium subterraneume0
- Treatment
- (NH4)2SO4e0
- Outcome
- acidificatione0
- Direction
- moree0
- Value
- 0.35–0.46 unitse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“subterranean clover grown with (NH4)2SO4 caused more acidification by 0.35–0.46 units in the top 10 cm”
Claim · model-written summary
Ammonium sulfate caused less subsoil acidification under clover.
- Taxon
- subterranean cloverTrifolium subterraneume1
- Treatment
- (NH4)2SO4e1
- Outcome
- acidificatione0
- Direction
- lesse0
- Value
- 0.14–0.19 unitse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“less acidification by 0.14–0.19 units in the 20–50 cm layer”
e1“subterranean clover grown with (NH4)2SO4”