Abstract
Yield decline or stagnation under long-term cultivation and its relationship with soil organic matter fractions are rarely considered. To understand this phenomenon, soil organic matter fractions and soil aggregate size distribution were studied in a long-term experiment at Akola, in a Vertisol in a semiarid tropical environment. For 14 years, the following fertiliser treatments were compared with undisturbed fallow plots: unfertilised (control), 100% recommended rates of N, NP, NPK (N : P : K ratios of 100 : 21.8 : 18.2 and 120 : 26.2 : 50 kg/ha for sorghum and wheat, respectively) and 100% NPK plus farmyard manure (FYM) and continuous cropping with a sorghum (Sorghumbicolor L. Moench) and wheat (Triticumaestivum L.) system during 1988–2001. The significant negative yield trend was observed in unbalanced use of inorganic N application for both crops. However, yields were maintained when NPK and NPK + FYM were applied. Results showed that soil organic C and total N in the unfertilised plot decreased by 21.7 and 18.2%, compared to the initial value, at a depth of 0–15 cm. Depletion of large macroaggregates (>2 mm) accounted for 22–81% of the total mass of aggregates in N, NP and unfertilised control plots compared to fallow plots. Irrespective of treatments, small macroaggregates (0.25–2 mm) dominated aggregate size distribution (56–71%), followed by microaggregates (0.053–0.25 mm, 18–37%). Active fractions, such as microbial biomass C, microbial biomass N, hot water soluble C and N, and acid hydrolysable carbohydrates were greater in NPK and NPK + FYM treatments than in the control. Carbon and N mineralisation were greater in small macroaggregates than microaggregates. Particulate organic matter C (POMC) and N (POMN) were significantly correlated (P < 0.01) with water-stable aggregate C and N (0.25–2 mm size classes), respectively. It was further observed that POMC and POMN were significantly greater in NPK and NPK + FYM plots than N and NP treated plots. Microbial biomass C was positively correlated with acid-hydrolysable carbohydrates (r = 0.79, P < 0.05). Continuous cropping and fertiliser use also influenced humic acid C and fulvic acid C fractions of the soil organic matter. Acid-hydrolysable N proportion in humic acid was greater than fulvic acid and it was greatest in NPK + FYM treatments. Continuous application of 100% NPK + FYM could restore soil organic carbon (SOC) to a new equilibrium level much earlier (t = 1/k, 2.4 years) than N (t = 1/k, 25.7 years), NP (t = 1/k, 8.1 years) and NPK (t = 1/k, 5.02 years). In conclusion, integrated use of NPK with FYM would be vital to obtain sustainable yields without deteriorating soil quality.
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Claims 18
Claim · model-written summary
Unbalanced inorganic N application had a significant negative yield trend in both crops.
SorghumNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The significant negative yield trend was observed in unbalanced use of inorganic N application for both crops.”
t0“sorghum”
Claim · model-written summary
NPK maintained crop yields.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“yields were maintained when NPK and NPK + FYM were applied.”
t0“sorghum”
Claim · model-written summary
NPK plus FYM maintained crop yields.
- Taxon
- wheat
Triticum aestivumt0 - Treatment
- NPK + FYMe0
- Outcome
- yieldse0
- Direction
- maintainede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“yields were maintained when NPK and NPK + FYM were applied.”
t0“wheat”
Claim · model-written summary
Soil organic C in unfertilized plots decreased 21.7% from initial value.
- Treatment
- unfertilisede0
- Outcome
- soil organic Ce0
- Direction
- decreasede0
- Value
- 21.7e0
- Comparator
- initial valuee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soil organic C and total N in the unfertilised plot decreased by 21.7 and 18.2%, compared to the initial value, at a depth of 0–15 cm.”
t0“sorghum”
Claim · model-written summary
Total soil N in unfertilized plots decreased 18.2% from initial value.
- Taxon
- wheatTriticum aestivumt0
- Treatment
- unfertilisede0
- Outcome
- total Ne0
- Direction
- decreasede0
- Value
- 18.2%e0
- Comparator
- initial valuee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soil organic C and total N in the unfertilised plot decreased by 21.7 and 18.2%, compared to the initial value, at a depth of 0–15 cm.”
t0“wheat”
Claim · model-written summary
Large macroaggregates were depleted by 22–81% under N, NP and unfertilized treatments relative to fallow.
- Treatment
- N, NP and unfertilised controle0
- Outcome
- large macroaggregatese0
- Direction
- Depletione0
- Value
- 22–81%e0
- Comparator
- fallow plotse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Depletion of large macroaggregates (>2 mm) accounted for 22–81% of the total mass of aggregates in N, NP and unfertilised control plots compared to fallow plots.”
t0“sorghum”
Claim · model-written summary
Small macroaggregates dominated aggregate size distribution across treatments.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Irrespective of treatments, small macroaggregates (0.25–2 mm) dominated aggregate size distribution (56–71%)”
t0“sorghum”
Claim · model-written summary
Microaggregates followed small macroaggregates in abundance.
- Taxon
- wheatTriticum aestivumt0
- Outcome
- microaggregatese0
- Value
- 18–37%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“followed by microaggregates (0.053–0.25 mm, 18–37%).”
t0“wheat”
Claim · model-written summary
Microbial biomass C, microbial biomass N, hot water soluble C and N, and acid hydrolysable carbohydrates were greater under NPK than control.
- Treatment
- NPKe0
- Outcome
- microbial biomass C, microbial biomass N, hot water soluble C and N, and acid hydrolysable carbohydratese0
- Direction
- greatere0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Active fractions, such as microbial biomass C, microbial biomass N, hot water soluble C and N, and acid hydrolysable carbohydrates were greater in NPK and NPK + FYM treatments than in the control.”
t0“sorghum”
Claim · model-written summary
Active soil organic fractions were greater under NPK plus FYM than control.
- Taxon
- wheatTriticum aestivumt0
- Treatment
- NPK + FYMe0
- Outcome
- microbial biomass C, microbial biomass N, hot water soluble C and N, and acid hydrolysable carbohydratese0
- Direction
- greatere0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Active fractions, such as microbial biomass C, microbial biomass N, hot water soluble C and N, and acid hydrolysable carbohydrates were greater in NPK and NPK + FYM treatments than in the control.”
t0“wheat”
Claim · model-written summary
Carbon and N mineralisation were greater in small macroaggregates than microaggregates.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Carbon and N mineralisation were greater in small macroaggregates than microaggregates.”
t0“sorghum”
Claim · model-written summary
Particulate organic matter C and N were significantly correlated with water-stable aggregate C and N.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Particulate organic matter C (POMC) and N (POMN) were significantly correlated (P < 0.01) with water-stable aggregate C and N (0.25–2 mm size classes), respectively.”
t0“sorghum”
Claim · model-written summary
POMC and POMN were significantly greater under NPK and NPK plus FYM than N and NP.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“POMC and POMN were significantly greater in NPK and NPK + FYM plots than N and NP treated plots.”
t0“sorghum”
Claim · model-written summary
Microbial biomass C was positively correlated with acid-hydrolysable carbohydrates.
- Outcome
- Microbial biomass Ce0
- Direction
- positively correlatede0
- Value
- r = 0.79e0
- Comparator
- acid-hydrolysable carbohydratese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Microbial biomass C was positively correlated with acid-hydrolysable carbohydrates (r = 0.79, P < 0.05).”
t0“sorghum”
Claim · model-written summary
Cropping and fertilizer influenced humic and fulvic acid C fractions.
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Continuous cropping and fertiliser use also influenced humic acid C and fulvic acid C fractions of the soil organic matter.”
t0“sorghum”
Claim · model-written summary
Acid-hydrolysable N proportion was greater in humic than fulvic acid and greatest under NPK plus FYM.
- Treatment
- NPK + FYMe0
- Outcome
- Acid-hydrolysable N proportione0
- Direction
- greatere0
- Comparator
- fulvic acide0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Acid-hydrolysable N proportion in humic acid was greater than fulvic acid and it was greatest in NPK + FYM treatments.”
t0“sorghum”
Claim · model-written summary
NPK plus FYM restored soil organic carbon to a new equilibrium earlier than N, NP or NPK.
- Treatment
- 100% NPK + FYMe0
- Outcome
- soil organic carbon (SOC)e0
- Direction
- much earliere0
- Value
- 2.4 yearse0
- Comparator
- Ne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Continuous application of 100% NPK + FYM could restore soil organic carbon (SOC) to a new equilibrium level much earlier (t = 1/k, 2.4 years) than N (t = 1/k, 25.7 years), NP (t = 1/k, 8.1 years) and NPK (t = 1/k, 5.02 years).”
t0“sorghum”
Claim · model-written summary
Integrated NPK and FYM is recommended for sustainable yield without soil deterioration.
- Outcome
- integrated use of NPK with FYMe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“integrated use of NPK with FYM would be vital to obtain sustainable yields without deteriorating soil quality.”
t0“sorghum”
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