Abstract
Sweet sorghum is a C4 plant with great biomass potential yield in semi-arid environments. Under growing conditions affected by water shortage and nutrient deficiency, the optimal combination of irrigation and nitrogen (N) fertilization rate is a central issue for sustainable farming systems. In this paper, a N balance study was applied to sweet sorghum cv. Keller, managed under three irrigation levels (I0, I50, I100: 0, 50, and 100% crop evapotranspiration—ETc restoration) and four N-fertilization rates (N0, N60, N120, N180: 0, 60, 120, and 180 kg ha−1). The 15N-labelled fertilization technique was used to assess the fate of N fertilizer within the agroecosystem. Dry biomass yield was significantly affected by the irrigation, while N rates had no effect. Across N and irrigation levels, the isotopic composition showed that approximately 34% of N applied by fertilization was used by the crop, 56% remained in the soil at the end of the cropping season, 1.83% was leached as nitrate, and 1.72% was volatilized as ammonia. N-fertilizer uptake was the lowest in I0, while in N0, the soil was strongly N-impoverished since sorghum showed a great aptitude to benefit from the soil N reserve. An even N input/output system (i.e., N-output corresponded to N-input) was observed in the N120 treatment, and the soil N reserve remained unchanged, while the system was N-enriched (positive input/output) in N180. However, although beneficial for crop nutrition and soil N reserve for subsequent crops in rotation, the N180 treatment is unsustainable due to many environmental side effects in the agroecosystem.
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Claims 11
Claim · model-written summary
Irrigation significantly affected dry biomass yield.
Not reportedComparatorDirection
Verbatim
e0“Dry biomass yield was significantly affected by the irrigation”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
N rates had no effect on dry biomass yield.
Not reportedComparator
Verbatim
e0“while N rates had no effect.”
e1“sweet sorghum cv. Keller”
e2“Dry biomass yield was significantly affected by the irrigation, while N rates had no effect.”
Claim · model-written summary
About 34% of fertilizer N was used by the crop.
Verbatim
e0“approximately 34% of N applied by fertilization was used by the crop”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
About 56% of fertilizer N remained in soil at season end.
Verbatim
e0“56% remained in the soil at the end of the cropping season”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
About 1.83% of fertilizer N leached as nitrate.
Verbatim
e0“1.83% was leached as nitrate”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
About 1.72% of fertilizer N volatilized as ammonia.
Verbatim
e0“1.72% was volatilized as ammonia”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
Fertilizer N uptake was lowest at I0.
Not reportedComparator
Verbatim
e0“N-fertilizer uptake was the lowest in I0”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
At N0, sorghum drew strongly on soil N reserves, impoverishing soil N.
- Taxon
- sweet sorghum cv. Kellere1
- Treatment
- N0e0
- Outcome
- soil was strongly N-impoverishede0
- Direction
- N-impoverishede0
Not reportedComparator
Verbatim
e0“in N0, the soil was strongly N-impoverished since sorghum showed a great aptitude to benefit from the soil N reserve”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
At N120, N output matched input and soil N reserves were unchanged.
Verbatim
e0“An even N input/output system (i.e., N-output corresponded to N-input) was observed in the N120 treatment, and the soil N reserve remained unchanged”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
At N180, the system was enriched in nitrogen.
Not reportedComparator
Verbatim
e0“the system was N-enriched (positive input/output) in N180”
e1“sweet sorghum cv. Keller”
Claim · model-written summary
Authors judged N180 unsustainable because of environmental side effects.
Verbatim
e0“the N180 treatment is unsustainable due to many environmental side effects in the agroecosystem.”
e1“sweet sorghum cv. Keller”
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