Abstract
Sustainability of maize-based cropping systems is a major challenge for southern Africa, yet the demand for maize as staple food and animal feed in the region continues to increase. A study was conducted on a sandy clay loam (220 g clay kg-1 soil) at Domboshawa in Zimbabwe to investigate the long-term effects of organic resource quality and application rate, and nitrogen (N) fertilization on soil chemical properties and maize (Zea mays L.) productivity. Crotalaria juncea (high quality), Calliandra calothyrsus (medium quality), cattle manure (variable quality), maize stover and Pinus patula sawdust (both low quality) were incorporated into soil at 4.0 t C ha-1 (high rate) and 1.2 t C ha-1 (low rate) at the start of each cropping season for nine consecutive years. At both high and low application rates, each of the five organic resources was applied in combination with or without mineral nitrogen (N) fertilizer at 120 kg N ha-1. The nine-year period saw maize grain yields declining by 22% to 84% across treatments despite increases in soil organic carbon, total N and available P from 6% to 80%. Crotalaria, Calliandra and manure led to a less steep yield decline. Exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and soil pH explained much of the variation in yield patterns observed under the different organic resource applications. Maize grain yield was positively correlated with exchangeable Ca (r = 0.51), Mg (r = 0.62) and K (r = 0.53), and soil pH (r = 0.49), but negatively correlated with other soil properties over the 9-year period. We concluded that declining soil exchangeable basic cations were the underlying causes of decreasing maize productivity, and was aggravated by use of low rates of organic resource inputs, particularly with N fertilization. Current nutrient management and fertilizer recommendations that emphasize inorganic N, P and K significantly undervalue the role played by organic resources in sustainability of maize cropping systems in southern Africa.
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Claims 11
Claim · model-written summary
Maize grain yields declined 22% to 84% across treatments over nine years.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The nine-year period saw maize grain yields declining by 22% to 84% across treatments”
Claim · model-written summary
Soil organic carbon, total N and available P increased 6% to 80% despite declining maize yields.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The nine-year period saw maize grain yields declining by 22% to 84% across treatments despite increases in soil organic carbon, total N and available P from 6% to 80%”
Claim · model-written summary
Crotalaria, Calliandra and manure had a less steep maize yield decline.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Crotalaria, Calliandra and manure led to a less steep yield decline.”
t0“maize productivity”
Claim · model-written summary
Exchangeable Ca, Mg and K and soil pH explained much of the variation in maize yield patterns.
Not reportedSettingDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and soil pH explained much of the variation in yield patterns observed under the different organic resource applications.”
t0“maize productivity”
Claim · model-written summary
Maize grain yield correlated positively with exchangeable Ca.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Maize grain yield was positively correlated with exchangeable Ca (r = 0.51)”
Claim · model-written summary
Maize grain yield correlated positively with exchangeable Mg.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Maize grain yield was positively correlated with exchangeable Ca (r = 0.51), Mg (r = 0.62)”
Claim · model-written summary
Maize grain yield correlated positively with exchangeable K.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Maize grain yield was positively correlated with exchangeable Ca (r = 0.51), Mg (r = 0.62) and K (r = 0.53)”
Claim · model-written summary
Maize grain yield correlated positively with soil pH.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Maize grain yield was positively correlated with exchangeable Ca (r = 0.51), Mg (r = 0.62) and K (r = 0.53), and soil pH (r = 0.49)”
Claim · model-written summary
Maize grain yield correlated negatively with other soil properties over nine years.
- Outcome
- Maize grain yielde0
- Direction
- negativelye0
- Qualifier
- other soil properties over the 9-year periode0
- Setting
- soile0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Maize grain yield was positively correlated with exchangeable Ca (r = 0.51), Mg (r = 0.62) and K (r = 0.53), and soil pH (r = 0.49), but negatively correlated with other soil properties over the 9-year period.”
Claim · model-written summary
Authors attributed declining maize productivity to declining exchangeable basic cations, aggravated by low organic input rates and N fertilization.
- Compound
- exchangeable basic cationse0
- Outcome
- decreasing maize productivitye0
- Direction
- decreasinge0
- Qualifier
- low rates of organic resource inputs, particularly with N fertilizatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“declining soil exchangeable basic cations were the underlying causes of decreasing maize productivity, and was aggravated by use of low rates of organic resource inputs, particularly with N fertilization”
Claim · model-written summary
Authors concluded that current N, P and K fertilizer recommendations significantly undervalue organic resources in maize cropping sustainability.
- Outcome
- the role played by organic resources in sustainability of maize cropping systemse0
- Setting
- southern Africae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Current nutrient management and fertilizer recommendations that emphasize inorganic N, P and K significantly undervalue the role played by organic resources in sustainability of maize cropping systems in southern Africa.”
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