poster61: dynamics of nitrogen and phosphorus in quensungual slash and mulch agroforestry system

A. Castro1, N. Asakawa1, G. Borrero1, I.M. Rao1, J.C. Menjívar2, E. Barrios3, E. Amézquita4, E. García5 and M. Ayarza4

(1) CIAT-Colombia; (2) National University of Colombia – Palmira; (3) EMBRAPA, Brazil; (4)CORPOICA, Colombia; (5) CIAT-Honduras

Consortium for the Integrated Management of

Soils in Central America

The Quesungual Slash and Mulch Agroforestry System (QSMAS) is a

smallholder production system with a group of technologies for the

sustainable management of soil, water and nutrients in drought-

prone areas in hillsides of the sub-humid tropics.

QSMAS is practiced in southwest Honduras (Central America),

where it has successfully replaced the non-sustainable,

environmentally unfriendly slash-and-burn (SB) traditional system.

The main objective of this study was to determine the effect of the

components of QSMAS and the principles (no SB, permanent soil

cover, minimal disturbance of soil and efficient use of fertilizer) that define its

management on the dynamics of nitrogen (N) and phosphorus (P), and the impact of

these dynamics on the productivity and sustainability of the system in Honduras.

Research was conducted to compare 5 land use systems:

1= Slash-and-burn (traditional production system);

2, 3 & 4= QSMAS of <2 years, 5-7 years and >10 years old, respectively; and

5= Secondary forest (reference land use system)

Measurements included: (1) determination of decomposition and

nutrient release from biomass of trees, shrubs and both annual

crops (Wieder and Lang,1982), using the litterbag technique (Bocock and

Gilbert, 1957); (2) ex situ N aerobic mineralization to measure the

potential conversion of organic N into inorganic forms available for plant uptake

(Anderson and Ingram, 1993); (3) ex situ partition of soil total P to measure the size of

different pools with varying levels of availability, following a sequential fractionation

(Tiessen and Moir, 1993; (4) ex situ size-density fractionation of soil organic matter

(SOM) as indicator of potential functional activity of SOM (Meijboom et al., 1995;

Barrios et al., 1996); (5) ex situ nutrient partitioning of crop biomass, to measure the

contribution of annual crops in the reference site to N and P cycling and balance; and

(6) in situ determination of crop yield in the different land use systems.

SB and QSMAS were managed applying local practices to produce

maize (Z. mays) and common bean (P. vulgaris), with and without

addition of fertilizers. Fertilized treatments include 49 kg N + 55

kg P ha-1 8-10 days after planting (DAP) and 52 kg N ha-1 ~30 DAP

for maize; and 46 kg N + 51 kg P ha-1 8-10 DAP for common bean.

QSMAS plot bordered by forests

regenerated as result of

elimination of slash and burn

ANDERSON JM and INGRAM JSI (eds.). 1993. Tropical soil biology and fertility - A handbook of methods. CAB International,

Wallingford, Oxon, UK. 221p; BARRIOS E, BURESH RJ and SPRENT JI. 1996. Organic matter in soil particle size and density

fractions from maize and legume cropping systems. Soil Biol Biochem, 28(2):185-193; BOCOCK KL and GILBERT OJW. 1957.

The disappearance of leaf litter under different woodland conditions. Plant Soil 9:179–188; MEIJBOOM FW, HASSINK J and

NOORDWIJK M. 1995. Density fractionation of soil macroorganic matter using silica suspensions. Soil Biol Biochem, 27:

1109 –1111; TIESSEN H and MOIR J.O. 1993. Characterization of available P by sequential extraction. In (M.R. Carter, Ed.),

Soil Sampling and Methods of Analysis. pp 75-86. Lewis Publishers, FLA, EEUU; WIEDER RK and LANG EL. 1982. A critique of

the analytic methods used in examining decomposition data obtained from litter bags. Ecology 63, 1636-1642.

This study was part of the project ‘PN15: Quesungual Slash and Mulch Agroforestry

System (QSMAS): Improving crop water productivity, food security and resource quality

in the sub-humid tropics’ funded by the Challenge Program on Water and Food of CGIAR.

It was co-executed by CIAT; MIS consortium (Central America); and National University of

Colombia (Palmira). We thank E. Melo, D. Vásquez, O. Ayala, F.J. Sánchez, J. Quintero,

J.G. Cobo and M.T. Trejo for their contributions to this work.

•Similarities in N dynamics in Quesungual and slash-and-burn systems indicate

that they were equally effective in providing N, although in Quesungual system

it is more the result of a biologically mediated process than of an accelerated

source through burning.

•Compared to slash-and-burn system, P pools of Quesungual system are more

dynamic and favorable for crop production by reducing their flows towards

unavailable forms.

•Based on the availability of nutrients and grain yields over time, Quesungual

system may be recommended as an option to replace the traditional slash-and-

burn system.

S lash and B u rn Q S M A S < 2 Q S M A S 5 -7 Q S M A S > 10

Gra

in y

ield

(t

ha

-1)

0 .0

0 .5

1 .0

1 .5

2 .0

2 .5

3 .0

Nitrogen: Total N content in soil (a) was similar among production

systems, with a tendency to be increased in QSMAS over time. N

mineralization (b) was higher in QSMAS >10 at 8 DAP, just before the

first fertilization. Bars in (a) indicate standard deviation.

Land U se S ys tem

S lash & B u rn Q S M A S < 2 Q S M A S 5 -7 Q S M A S > 10 S ec . F o res t

N c

on

ten

t (m

g N

kg

-1 s

oil)

0

500

1000

1500

2000

2500

3000

3500

LSD 0.05 = ns

In cuba tion (days )

0 4 8 12 16 20 24 28 32

N m

ine

raliz

ati

on

(m

g N

kg

-1 s

oil

0

10

20

30

40

50

S lash & B u rn

Q S M A S < 2

Q S M A S 5 -7

Q S M A S > 10

S ec . F o res t

ns ns ns

Mineralization: Decomposition of (a), and release of N (b) and P (c)

from a mixture of vegetative materials of different quality (good,

intermediate and poor) according to the C:N ratio, were similar

among systems. For QSMAS, this suggest an effective biological

activity and nutrient cycling over time.

P release rate (week-1) DSM0.05=

T im e (w eeks)

0 1 2 4 8 16 32 480 1 2 4 8 16 32 480 1 2 4 8 16 32 48

N r

ele

as

e (

%)

0

20

40

60

80

100

T im e (w eeks)

0 1 2 4 8 16 32 480 1 2 4 8 16 32 480 1 2 4 8 16 32 48

N r

ele

as

e (

%)

0

20

40

60

80

100N release rate per week-1:

Slash and Burn = 0.022

QSMAS <2 = 0.032

QSMAS 5-7 = 0.029

QSMAS >10 = 0.035

Sec. Forest = 0.031

DSM0.05 = ns

P release rate per week-1:

Slash and Burn = 0.043

QSMAS <2 = 0.051

QSMAS 5-7 = 0.052

QSMAS >10 = 0.050

Sec. Forest = 0.051

DSM0.05 = ns

S lash and Burn

Q SM AS <2

Q SM AS 5-7

Q SM AS >10

Sec. Forest

M aize - Q SM AS +F

M aize - S lash and Burn -F

Com m on bean - S lash and Burn -F

Com m on bean - Q SM AS +F

M aize - Q SM AS +F

M aize - S lash and Burn -F

Com m on bean - S lash and Burn -F

Com m on bean - Q SM AS +F

M aize - Q SM AS +F

M aize - S lash and Burn -F

Com m on bean - S lash and Burn -F

Com m on bean - Q SM AS +F

LSD0.05= LSD0.05=0.67 ns

(a) (b)

Land U se S ys tem

S lash & B u rn Q S M A S < 2 Q S M A S 5 -7 Q S M A S > 10 S ec . F o res t

P c

on

ten

t b

y p

oo

l (%

)

0

20

40

60

80

100

L a n d U se S ys te m

S lash & B u rn Q S M A S < 2 Q S M A S 5 -7 Q S M A S > 10 S ec . F o res t

P c

on

ten

t b

y p

oo

l (m

g P

kg

-1 s

oil)

0

5 0

1 0 0

1 5 0

2 0 0

2 5 0

3 0 0

3 5 0

4 0 0

Phosphorus: Total P content (a) in QSMAS increased across time,

while the proportion of organic and inorganic P pools (b) remained

similar among land use systems. AP= Available P; MAP= Moderately

available P; RP= Residual P. TP= Total P (sum of the above)

MAP= 14.5LSD0.05 : AP= 12.7

RP= 24.1

TP= 40.7 LSD0.05: Inorganic P=3.0Organic P= 3.0(a) (b)

Land U se S ys tem

S lash & B u rn Q S M A S < 2 Q S M A S 5 -7 Q S M A S > 10 S ec . F o res t

SO

M c

on

ten

t b

y p

oo

l (g

po

ol

kg

-1 s

oil)

0

1

2

3

4

5

6

7

8

9

10

L a n d U se S ys te m

S lash & B u rn Q S M A S < 2 Q S M A S 5 -7 Q S M A S > 10 S ec . F o res t

SO

M c

on

ten

t (%

)

0

1

2

3

4

5

6

LSD 0.05 = 1.29(a) (b) LM= nsLSD0.05 : LL=2.0 LH= ns

(a)

(c)(b)

Grain yield: Under the traditional practices used to produce maize

and common bean in the SB system (where the source of nutrients are

ashes after burning) and QSMAS (in which nutrients are provided by

fertilizers and biomass from native species of tress and crop

residues), yields of maize were higher in QSMAS (although they

decrease over time). Yields in common bean were consistently low in

SB system and QSMAS due to low yield potential of the landrace used.

Bars indicate standard deviation.

Soil Organic Matter (SOM): Total SOM content (a) in QSMAS increased

over time. The biologically active fraction of SOM (light fraction, LL)

was reduced in the production systems compared with the secondary

forest (b). LM= intermediate fraction and LH= heavy fraction (humus).

T im e (w eeks)

0 1 2 4 8 16 32 480 1 2 4 8 16 32 480 1 2 4 8 16 32 48

Ex

ten

t o

f d

ec

om

po

sit

ion

(%

)

0

20

40

60

80

100

Decomposition rate per week-1:

Slash and Burn = 0.024

QSMAS <2 = 0.031

QSMAS 5-7 = 0.030

QSMAS >10 = 0.030

Sec. Forest = 0.025

DSM0.05 = ns

•Based over a three year time period

•Focused on the TRADITIONAL production systems

(i.e. SB no fertilized and QSMAS fertilized)