Limits...
Tightly-Coupled Plant-Soil Nitrogen Cycling: Comparison of Organic Farms across an Agricultural Landscape.

Bowles TM, Hollander AD, Steenwerth K, Jackson LE - PLoS ONE (2015)

Bottom Line: How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a central challenge for reducing the tradeoffs often associated with N cycling in agriculture.Thus tightly-coupled N cycling occurred on several working organic farms.Novel combinations of N cycling indicators (i.e. inorganic N along with soil microbial activity and root gene expression for N assimilation) would support adaptive management for improved N cycling on organic as well as conventional farms, especially when plant-soil N cycling is rapid.

View Article: PubMed Central - PubMed

Affiliation: Department of Land, Air and Water Resources, University of California Davis, Davis, California, United States of America.

ABSTRACT
How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a central challenge for reducing the tradeoffs often associated with N cycling in agriculture. Variability in soil organic matter and management of organic farms across an agricultural landscape may yield insights for improving N cycling and for evaluating novel indicators of N availability. We assessed yields, plant-soil N cycling, and root expression of N metabolism genes across a representative set of organic fields growing Roma-type tomatoes (Solanum lycopersicum L.) in an intensively-managed agricultural landscape in California, USA. The fields spanned a three-fold range of soil carbon (C) and N but had similar soil types, texture, and pH. Organic tomato yields ranged from 22.9 to 120.1 Mg ha-1 with a mean similar to the county average (86.1 Mg ha-1), which included mostly conventionally-grown tomatoes. Substantial variability in soil inorganic N concentrations, tomato N, and root gene expression indicated a range of possible tradeoffs between yields and potential for N losses across the fields. Fields showing evidence of tightly-coupled plant-soil N cycling, a desirable scenario in which high crop yields are supported by adequate N availability but low potential for N loss, had the highest total and labile soil C and N and received organic matter inputs with a range of N availability. In these fields, elevated expression of a key gene involved in root N assimilation, cytosolic glutamine synthetase GS1, confirmed that plant N assimilation was high even when inorganic N pools were low. Thus tightly-coupled N cycling occurred on several working organic farms. Novel combinations of N cycling indicators (i.e. inorganic N along with soil microbial activity and root gene expression for N assimilation) would support adaptive management for improved N cycling on organic as well as conventional farms, especially when plant-soil N cycling is rapid.

No MeSH data available.


Soil inorganic N, microbial biomass C (MBC) and K2SO4 extractable organic C (EOC) from surface soil (0–15 cm depth).Soils were sampled at three times across 13 organically-managed Roma-type tomato fields in Yolo Co., California, USA. For ammonium and nitrate (NH4+-N and NO3--N), shown are back-transformed means and 95% confidence intervals. For MBC and EOC, shown are means and 95% confidence intervals. In order to increase resolution of the majority of the data, two means are not shown, both from field 4. NH4+-N at pre-transplant in field 4 was 30.5 μg N g-1 (6.5 < μ < 131.8) and NO3--N at mid-season in field 4 was 35.0 μg N g-1 (14.5 < μ < 82.7).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4487741&req=5

pone.0131888.g004: Soil inorganic N, microbial biomass C (MBC) and K2SO4 extractable organic C (EOC) from surface soil (0–15 cm depth).Soils were sampled at three times across 13 organically-managed Roma-type tomato fields in Yolo Co., California, USA. For ammonium and nitrate (NH4+-N and NO3--N), shown are back-transformed means and 95% confidence intervals. For MBC and EOC, shown are means and 95% confidence intervals. In order to increase resolution of the majority of the data, two means are not shown, both from field 4. NH4+-N at pre-transplant in field 4 was 30.5 μg N g-1 (6.5 < μ < 131.8) and NO3--N at mid-season in field 4 was 35.0 μg N g-1 (14.5 < μ < 82.7).

Mentions: Soil NH4+ and NO3- pools were highly variable across fields, sampling times, and depths (Figs 3 and 4; S2 Table). For instance, soil NO3- at mid-season (when tomato N demand is highest) ranged from a low of 0.2 μg N g-1 (0.0 < μ < 0.5; mean ± 95% CI) in field 1 to a high of 35.0 μg N g-1 (14.5 < μ < 82.7) in field 4 (Fig 3), which also had very high pre-transplant levels of NH4+. In general, surface soil NO3- concentrations tended to be lower and less variable at the low and high ends of the soil C gradient (e.g. fields 1, 2, 10, 11, 12, and 13) relative to fields in the middle of the gradient (Fig 4). Considering all fields collectively, the mean surface soil NO3- concentration was only 4.6 μg N g-1 (3.4 < μ < 6.2) at midseason, which was similar to the values at transplant and harvest (Fig 3). Soil NO3- declined significantly with depth, with the lowest mean value of 0.6 μg N g-1 (0.5 < μ < 0.8) at harvest in the 30–75 cm depth. For the individual fields, soil NH4+ was less variable than NO3- in the 0–15 cm depth (Fig 4). Considering all fields collectively, soil NH4+ declined significantly from pre-transplant to mid-season sampling at both the 0–15 cm and 15–30 cm depths and then remained similar at harvest (Fig 3).


Tightly-Coupled Plant-Soil Nitrogen Cycling: Comparison of Organic Farms across an Agricultural Landscape.

Bowles TM, Hollander AD, Steenwerth K, Jackson LE - PLoS ONE (2015)

Soil inorganic N, microbial biomass C (MBC) and K2SO4 extractable organic C (EOC) from surface soil (0–15 cm depth).Soils were sampled at three times across 13 organically-managed Roma-type tomato fields in Yolo Co., California, USA. For ammonium and nitrate (NH4+-N and NO3--N), shown are back-transformed means and 95% confidence intervals. For MBC and EOC, shown are means and 95% confidence intervals. In order to increase resolution of the majority of the data, two means are not shown, both from field 4. NH4+-N at pre-transplant in field 4 was 30.5 μg N g-1 (6.5 < μ < 131.8) and NO3--N at mid-season in field 4 was 35.0 μg N g-1 (14.5 < μ < 82.7).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4487741&req=5

pone.0131888.g004: Soil inorganic N, microbial biomass C (MBC) and K2SO4 extractable organic C (EOC) from surface soil (0–15 cm depth).Soils were sampled at three times across 13 organically-managed Roma-type tomato fields in Yolo Co., California, USA. For ammonium and nitrate (NH4+-N and NO3--N), shown are back-transformed means and 95% confidence intervals. For MBC and EOC, shown are means and 95% confidence intervals. In order to increase resolution of the majority of the data, two means are not shown, both from field 4. NH4+-N at pre-transplant in field 4 was 30.5 μg N g-1 (6.5 < μ < 131.8) and NO3--N at mid-season in field 4 was 35.0 μg N g-1 (14.5 < μ < 82.7).
Mentions: Soil NH4+ and NO3- pools were highly variable across fields, sampling times, and depths (Figs 3 and 4; S2 Table). For instance, soil NO3- at mid-season (when tomato N demand is highest) ranged from a low of 0.2 μg N g-1 (0.0 < μ < 0.5; mean ± 95% CI) in field 1 to a high of 35.0 μg N g-1 (14.5 < μ < 82.7) in field 4 (Fig 3), which also had very high pre-transplant levels of NH4+. In general, surface soil NO3- concentrations tended to be lower and less variable at the low and high ends of the soil C gradient (e.g. fields 1, 2, 10, 11, 12, and 13) relative to fields in the middle of the gradient (Fig 4). Considering all fields collectively, the mean surface soil NO3- concentration was only 4.6 μg N g-1 (3.4 < μ < 6.2) at midseason, which was similar to the values at transplant and harvest (Fig 3). Soil NO3- declined significantly with depth, with the lowest mean value of 0.6 μg N g-1 (0.5 < μ < 0.8) at harvest in the 30–75 cm depth. For the individual fields, soil NH4+ was less variable than NO3- in the 0–15 cm depth (Fig 4). Considering all fields collectively, soil NH4+ declined significantly from pre-transplant to mid-season sampling at both the 0–15 cm and 15–30 cm depths and then remained similar at harvest (Fig 3).

Bottom Line: How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a central challenge for reducing the tradeoffs often associated with N cycling in agriculture.Thus tightly-coupled N cycling occurred on several working organic farms.Novel combinations of N cycling indicators (i.e. inorganic N along with soil microbial activity and root gene expression for N assimilation) would support adaptive management for improved N cycling on organic as well as conventional farms, especially when plant-soil N cycling is rapid.

View Article: PubMed Central - PubMed

Affiliation: Department of Land, Air and Water Resources, University of California Davis, Davis, California, United States of America.

ABSTRACT
How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a central challenge for reducing the tradeoffs often associated with N cycling in agriculture. Variability in soil organic matter and management of organic farms across an agricultural landscape may yield insights for improving N cycling and for evaluating novel indicators of N availability. We assessed yields, plant-soil N cycling, and root expression of N metabolism genes across a representative set of organic fields growing Roma-type tomatoes (Solanum lycopersicum L.) in an intensively-managed agricultural landscape in California, USA. The fields spanned a three-fold range of soil carbon (C) and N but had similar soil types, texture, and pH. Organic tomato yields ranged from 22.9 to 120.1 Mg ha-1 with a mean similar to the county average (86.1 Mg ha-1), which included mostly conventionally-grown tomatoes. Substantial variability in soil inorganic N concentrations, tomato N, and root gene expression indicated a range of possible tradeoffs between yields and potential for N losses across the fields. Fields showing evidence of tightly-coupled plant-soil N cycling, a desirable scenario in which high crop yields are supported by adequate N availability but low potential for N loss, had the highest total and labile soil C and N and received organic matter inputs with a range of N availability. In these fields, elevated expression of a key gene involved in root N assimilation, cytosolic glutamine synthetase GS1, confirmed that plant N assimilation was high even when inorganic N pools were low. Thus tightly-coupled N cycling occurred on several working organic farms. Novel combinations of N cycling indicators (i.e. inorganic N along with soil microbial activity and root gene expression for N assimilation) would support adaptive management for improved N cycling on organic as well as conventional farms, especially when plant-soil N cycling is rapid.

No MeSH data available.