Abstract
ABSTRACT This study was carried out to assess the carbon returned in soyabean crop residues as a function of soyabean maturity class and P fertilizer. Three levels of P were applied to four soyabean varieties in three replications at four sites. Late varieties gave greater root + litter C input than early and medium varieties, and their responses to P were larger. P application increased root + litter C by 44–49%, and total C, comprising C in soyabean root, litter and stover, by 45–46%. Root + litter C was 60% of total C input by soyabean. While soyabean was not able to maintain soil organic C (SOC) at an annual C input decomposition rate of 70%, the application of P provided 105–107% of the C input required to maintain SOC at 5.1 g kg−1 at C input decomposition rate of 50%. For the low SOC levels of 5.1–8.7 g kg−1 at the sites, it was estimated that total C inputs of 12.2–14.2 Mg ha−1 are required to increase organic C by 1 g kg−1. Depending on decomposition rate, however, total C input by the varieties was 7–22% of total C required to increase organic C by the same amount. Although the late varieties responded positively to P, the total C required to increase organic C by 1 g kg−1 was reduced by only 4–10% with the application of P. Organic C input by soyabean in a cereal-based cropping system remains minimal despite increased soyabean duration and the application of P.
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Claims 11
Claim · model-written summary
Late varieties gave greater root and litter carbon input.
Verbatim
e0“Late varieties gave greater root + litter C input than early and medium varieties”
t0“Soyabean”
Claim · model-written summary
Late varieties responded more strongly to phosphorus.
Verbatim
e0“their responses to P were larger”
e1“Late varieties gave greater root + litter C input than early and medium varieties”
t0“Soyabean”
Claim · model-written summary
Phosphorus increased root and litter carbon by 44–49%.
Not reportedComparator
Verbatim
e0“P application increased root + litter C by 44–49%”
t0“Soyabean”
Claim · model-written summary
Phosphorus increased total carbon input by 45–46%.
Not reportedComparator
Verbatim
e0“P application increased root + litter C by 44–49%, and total C, comprising C in soyabean root, litter and stover, by 45–46%”
Claim · model-written summary
Root and litter carbon formed 60% of total input.
Not reportedDirection
Verbatim
e0“Root + litter C was 60% of total C input by soyabean”
Claim · model-written summary
Soyabean could not maintain soil organic carbon at 70% annual decomposition.
Not reportedDirection
Verbatim
e0“soyabean was not able to maintain soil organic C (SOC) at an annual C input decomposition rate of 70%”
Claim · model-written summary
Phosphorus supplied 105–107% of carbon needed to maintain soil organic carbon under 50% decomposition.
- Taxon
- soyabeant0
- Treatment
- application of Pe0
- Outcome
- C input required to maintain SOCe0
- Value
- 105–107%e0
- Qualifier
- C input decomposition rate of 50%e0
Not reportedComparatorDirection
Verbatim
e0“application of P provided 105–107% of the C input required to maintain SOC at 5.1 g kg−1 at C input decomposition rate of 50%”
t0“Soyabean”
Claim · model-written summary
Increasing soil organic carbon by 1 g kg−1 was estimated to require 12.2–14.2 Mg ha−1 carbon.
Not reportedDirection
Verbatim
e0“total C inputs of 12.2–14.2 Mg ha−1 are required to increase organic C by 1 g kg−1”
t0“Soyabean”
Claim · model-written summary
Varietal carbon input represented 7–22% of the required input.
Not reportedDirection
Verbatim
e0“total C input by the varieties was 7–22% of total C required to increase organic C by the same amount”
t0“Soyabean”
Claim · model-written summary
Phosphorus reduced the carbon required to increase soil organic carbon by only 4–10%.
- Taxon
- soyabeant0
- Treatment
- application of Pe0
- Outcome
- total C required to increase organic Ce0
- Direction
- reducede0
- Value
- 4–10%e0
Not reportedComparator
Verbatim
e0“total C required to increase organic C by 1 g kg−1 was reduced by only 4–10% with the application of P”
t0“Soyabean”
Claim · model-written summary
Soyabean carbon input remained minimal despite greater duration and phosphorus.
Not reportedDirection
Verbatim
e0“Organic C input by soyabean in a cereal-based cropping system remains minimal despite increased soyabean duration and the application of P”