Can Plant Productivity and Resource Distribution of Silvopastures Be Regulated by Manipulating Tree Arrangement Without Changing Density?

Transcription

1 Can Plant Productivity and Resource Distribution of Silvopastures Be Regulated by Manipulating Tree Arrangement Without Changing Density? Solomon Ghezehei, JG Annandale, CS Everson June 03, 2015

2 INTRODUCTION Challenges: Crop & pasture production faces: Arable land Water Production technologies, inputs Pressure on natural grasslands Johannesburg Durban Cape Town George Study area

3 Required Production systems Suitable for marginal lands, land rehabilitation Resource efficient Produce alternative fodder, fuel wood Reduce pressure on natural grassland Species: Low water use Tolerance to marginal lands

4 Agroforestry (AF): Possible solution Trees (T) & crops (C) in a land unit Interactions: ecological, economic Potentially productive in marginal soils Hedgerow intercropping (HI) Humid, sub-humid tropics, temperate

5 Slow implementation in SA: Knowledge on T-C combinations, benefits Misconceptions about trees Consolidated support for AF policy WRC Project (K5/1480/1/12) Agroforestry systems for improved productivity through the efficient use of water Undertaking knowledge synthesis, experiments & modelling on selected agroforestry systems & technology transfer

6 Potential systems: Alley cropping, fodder banks, silvopasture Crops: Maize, cowpea, pumpkin, Guinea grass, weeping Trees: love grass, Pigeon pea, velvet bean, kikuyu Leucaena, mulberry, sweet thorn, fever tree, black wattle, Jatropha

7 Kikuyu (Pennisetum clandestinum) Robust, creeping, summer grass Exclusively for grazing Requires: RF 700 mm Tolerates mild frost Can support (per hectare) Dryland: 3 cows per for 5 months Irrigation & fertilizer: 6-7 cows for 7 months

8 Jatropha curcas Euphorbiaceae family (toxic) Small (< 8m tall); Fast growing Drought resistant, deciduous Can grow under low RF, low fertility, low altitude Uses: biodiesel source (Oil content 35%) Erosion control Live-fences

9 Higher yields in sub-tropical conditions Suitable along KZN coastal belt Earliest: months (good RF) Peak: 4-5 years Potential (mature): 2-3 t ha -1 (semi-arid) to 5 t ha -1 (high RF)

10 1-month old 2½-year old 11-year old

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12 OBJECTIVE: To understand interactions and productivity of HI systems by conducting measurements of soil water, solar radiation and plant productivity

13 Key Questions Can tree spacing/arrangement be manipulated without changing density in order to: 1. Minimize tree productivity reductions 2. Optimize distribution of radiation, soil water 3. Optimize crop growth

14 Ukulinga Altitude: 781 m RF: 680 mm 106 days (Winter 23%) Temp.: 18.4 C Summer: Warm - hot Winter: Mild; moderate frost Annual E: mm Warm, temperate with annual RF (Köppen class.)

15 Experiment RCBD: 3 blocks x 5 treatments Tree-only (JO) - Control Standard-square (SS) Single-row (SR) Double-row (DR) Triple-row (TR) Soil: Loam to clay loam BD = 1.58 g cm -3

16 Jan 2005 Feb 2005 May 2005 Weed control

17 SR; JO; SS 20 months after establishment

18 DR: within a row-set and the intercropped zone

19 Measurements Radiation: Tube solarimeters: N73 E S73 W JO: 0 m; 0.75 m: 1.5 m SR: 0 m; 0.83 m; 1.67 m; 2.5 m DR: 0 m; 1 m; 2 m; 3 m; 4 m Soil water: TDR Depth (m): 0.05; 0.15; 0.25; 0.40; 0.60 Plant parameters: Tree & grass

20 Radiation - Solarimeters Soil water TDR

21 J J A S O N D J F M A M J J A S O N D J F M A M J J A Mean Stem Diameter (m) Diameter growth Rainfall (mm) JO SS SR DR TR Rainfall (mm) Diameter growth was affected by BG interspecies competition but not spacing/arrangement

22 Effects of pruning Right after pruning (Oct 2007) 11 months after pruning (Sep 2008)

23 O N D J F M A M J J A S O Post-pruning height RGR(%) S O N D J F M A M J J A S O Post-pruning height (m) JO SR DR TR Post-pruning tree height JO: tallest SR: Shortest 40 JO SR DR TR After 1 year 30 JO: 20% taller

24 Harvest index (%) Yield (g tree -1 ) 340 JO SS SR DR TR a a bc bc b 85 a c 0 b b b b b b b b JO SS SR DR TR a Yield (kg ha -1 ) b b b b a b b b b JO SS SR DR TR

25 Radiation - Tree-ony (JO)

26 Soil Water (mm) JO Wet Period Dry Period m m 0 m 0.75 m 1.5 m Distance

27 Yield per cycle (t ha -1 ) Biomass (t ha -1 ) SR 4.5 Nov 17 - Dec 22 '06 Kikuyu harvest Cumulative Radiation b bc c c b a Radiation (MJ) Nov Jan Feb Mar Apr-08 Cumulative Cumulative Yield (t ha -1 ) Distance (m)

28 Soil Water (mm) SR Dry Period Wet Period m m m 0 m 0.83 m 1.67 m 2.5 m Distance

29 Yield per cycle (t ha -1 ) Biomass (t ha -1 ) DR 4.5 Harvest Nov 17 - Dec 22 '06 Cumulative Radiation a b c c bc ab Radiation (MJ) Nov Jan Feb Mar Apr-08 Cumulative Cumulative yield (t ha -1 ) Distance (m)

30 Soil Water (mm) DR Wet Period Dry Period m -3 m -2 m -1 m 0 m 1 m 2 m 3 m 4 m Distance (m)

31 Evapotranspiration Treatment Total ET (mm) JO 1019 SR 1171 DR 849

32 Cumulative radiation interception by trees (MJ) Cumulative irradiance at soil or intercepted by grass (MJ) JO 223 (27.1%) 600 SR 92 (11.2%) 731 DR 66 (8%) 757

33 Pasture (kikuyu) Radiation use efficiency (g MJ -1 ) SW NE Average SR 2.5 m m m m m m DR 4 m m m m m m WUE? Nuts (kg ha -1 ) AGDM (t ha -1 ) Grass (t ha -1 ) ET (m 3 ) JO SR DR

34 Conclusions BG interactions between trees & perennial grass were competitive, resulted in tree productivity reductions When nutrient was not limited, water was more limiting than radiation. Effects of BG competition on tree productivity could not be minimized by manipulating tree spacing only

35 Conclusion Radiation, water distribution, pasture growth across T-C interface can be optimized by changing tree spacing without changing density.

36 Water Research Commission of South Africa National Research Foundation of South Africa Thank you!!!

37 JO

38 Soil water - SR

39 Soil water - DR