Table 1: Nutrients potentially available through CA and various soil ecosystem processes
CA component and ecosystems services
Above-ground biomass / crop residues
(through microbial C transformation) 1
N (kg/ha)
168 P (kg/ha)
24 K (kg/ha)
249
(40% available for
next crop = 70) (20% available for
next crop in 1 st
year = 5) (SA soils have
sufficient K)
50 11 72
(20)
50
0 (2.2)
0
21 0
0
140
17
2380 28
40
1120 321
15
4815
Below-ground biomass of roots 2
SOM (2.5%; 20 kg N released per 1% SOM)
Nutrient cycling through microbes (e.g. with
high colonisation of AMF) 4
Nutrients available to next crop (kg/ha)
Nutrient Costs (R/kg)
Nutrient value (R/ha)
3
N fixed by legumes and available for next crop (10% legumes in mix) forms part of above-
ground biomass
1
Nutrient cycling by cover crop roots forms part of root biomass value
2
P and K could also be added; values will increase with higher SOM levels
3
This value has a great potential to increase in future as microbial diversity and activity rise
4
The nutrients available to the next crop in
the example illustrated in Table 1 are freely
supplied by the soil ecosystem functions and
services that have been influenced by the CA
system; these nutrients are valued at R8315.
This value will increase as CA practices are
optimized, SOM have increased, and other
soil ecosystem services have improved (such
as soil microbial recycling of nutrients). To
shorten the transformation period of restoring
these functions (e.g. in a degraded soil), quality
CA practices are needed that will speed-up the
biological process and time. In wetter areas
with clay soils this could take 3 to 5 years, but
in warmer areas with sandy soils, it could take
longer. In Part II of this article a case study
from Ottosdal, North West Province will be
described.
AgriKultuur |AgriCulture
References
Jones, C., 2017. Light Farming: Five Principles
for Soil Sequestration. Keynote address at
the 5 th Annual No-till Conference, Victoria,
Australia.
Jones, D. L., Nguyen C. & Finlay, R. D., 2009.
Carbon flow in the rhizosphere: carbon trading
at the soil–root interface. Plant Soil 321, 5–33.
Drinkwater, L.E. & Snapp, S.S., 2007.
Nutrients in agroecosystems: Rethinking the
management paradigm. Advances in Agronomy
92, 163–186.
Hoorman, J. & Islam, R., 2010. Understanding
soil microbes and nutrient recycling. Fact
Sheet SAG-16-10, Ohio State University.
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