Effects of conservation agriculture and

manure application on maize grain yield

and soil organic carbon: a comparative

analysis

Leonard Rusinamhodzi

PhD Student

Plant Production Systems Group

The challenge of soil fertility decline…. 70% of smallholder farms are on infertile sandy soils Majority of farmers use mouldboard ploughing

Time of cultivation (years)

0 5 10 15 20

SO

C (

t h

a-1)

30

40

50

60

70

80

90

Time of cultivation (years)

0 2 4 6 8 10 12 14 160

20

40

60

80

Clay soil Sandy soil

Source: Rusinamhodzi et al (2011)

Farmers’ response……….

Use of cattle

manure to improve

crop productivity

Use of crop

residues to improve manure

quantity and quality

of manure

Manure use………… Manure is spread on

soil surface and ploughed under

Some farmers are now applying manure in planting basins

Strategy make small quantities cover a large area

Crop residue use………

Crop residues produced

Left in fieldsCollected

Mulch (ex-situ)

Compost Livestock feed

Bedding BurntMulch

(in- situ)

Available for

livestockKraal

Burnt

40 ha 43 ha

3 ha 5.6 ha 13 ha 4.6 ha 13.5 ha1.1 ha 40 ha1.9 ha

Example: Manjonjo village, Murehwa, Zimbabwe

CR from 70% of cropped area is used for feed/bedding

Trade-offs ………………..

The allocation of crop residues for livestock feed meets two out of three critical objectives;

it ensures feed during the dry season

improves quantity and quality of manure

but does not ensure permanent soil cover required under conservation agriculture (CA).

Trade-offs……………… There are strong trade-offs for

either allocating crop residues for livestock feed or using the crop residues directly for mulch thereby reducing the amount and quality of manure available and compromising the condition of livestock

Study objective…….

To perform a comparative analysis of maize grain yield and soil organic carbon (SOC) changes in CA systems versus conventional tillage systems (with manure application).

• Crop yield- food security and income,

• SOC - important determinant of soil fertility, productivity and sustainability

Field experiments…………….

• Data obtained from two sets of long-term experiments under continuous sole maize (Zea mays L.) • experiment on manure application

under conventional tillage• Experiment on no-tillage with mulch

cover

Manure experiment

• Established from 2002 to 2010 on both clay (Chromic Luvisols) and sandy (Haplic Lixisols) soils and two field types (homefield and outfield) in Murehwa, Zimbabwe.

• Tillage- mouldboard ploughing • Fertiliser treatments

• control, • 100 kg N ha-1, • 100 kg N ha-1 + 5 t manure ha-1 • 100 kg N ha-1 + 15 t manure ha-1.

Tillage experiment• Established in 1988 to 1999 at three sites,

Domboshawa (sandy soils, Haplic Lixisols), Makoholi (sandy soils, Ferralic Arenosols) and Institute of Agricultural Engineering (IAE) (red clay soils, Chromic Luvisols)

• Two tillage treatments• Conventional mouldboard ploughing, 23 cm depth.

• Mulch ripping (MR), ripping to a depth of 20 – 25 cm , crop residues maintained on the soil surface (40 and 60 % cover).

• All treatments received 114 kg N ha-1, 22 kg P ha-1 and 25 kg K ha-1

Soil analysis

Total C was determined by dry combustion using a LECO TRUSPEC C and N auto-analyser (LECO Corporation, 2003).

Grain yield advantages were calculated as difference between yield in control and treatment

Results…….maize grain yield

Addition of 5 t ha-1 manure resulted in more than double maize grain yield over the control

Red clay soil (homefield)

100N 5T 15T

We

igh

ted

me

an

diffe

ren

ce

(t

ha

-1)

0

1

2

3

4

5

6Red clay soil (outfield)

100N 5T 15T0

1

2

3

4

5

6

Sandy soil (homefield)

Fertilization strategy

100N 5T 15T

We

igh

ted

me

an

diffe

ren

ce

(t

ha

-1)

-1

0

1

2

3

4

5Sandy soil (outfield)

Fertilization strategy

100N 5T 15T-1

0

1

2

3

4

5

Results……..maize grain yield

Effect of mulch and reduced tillage on yield was marginal with a yield gain of only 0.2 t ha-1 over a nine year period

Domboshawa Makoholi IAE PooledW

eigh

ted

mea

n di

ffere

nce

(t ha

-1)

-2

-1

0

1

2

3

Results…………SOC

Manure application (5 t ha-1) under conventional tillage increased SOC by 0.13% and 0.09% per year on clay and sandy soils respectively

0

0.5

1

1.5

2

2.5

3

3.5

4

Cont

rol 5t 15

t

Cont

rol 5t 15

t

Cont

rol 5t 15

t

Cont

rol 5t 15

t

Red HF Red OF Sandy HF Sandy OF

Soil

orga

nic c

arbo

n (%

)

Results………….SOC

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

CT Red clay MR Red clay CT sandy soil MR sandy soil

Soil o

rganic

carb

on (%

)

Reduced tillage and mulch retention led to an increase of 0.02% per year for both sandy and clay soils

Discussion points

the opportunity cost of losing mulch is offset by gains in animal productivity given that communal grazing is not adequate during the dry season

The results suggest that the decision by farmers to allocate crop residues to animals as feed and use manure is most suitable for their circumstances

manure application in combination with fertilizer provides calcium, magnesium and micronutrients that ensure high yields especially on degraded soils

Conclusion

• An optimal procedure for retaining adequate crop residues while providing sufficient feed for livestock is thus required to facilitate the adoption of CA on smallholder farms.

Thank you!