1. G. M. Sakala, V. Shitumbanuma, B. Kaninga Paper presented at the 1 st Africa Congress on Conservation Agriculture, Lusaka, Zambia, 18 th – 21 st March, 2014.

2. Introduction Yields on smallholder farms have remained low in Zambia, averaging around 1.5 - 2 t ha -1 Among other factors cited as contributing to the low production and productivity: poor land husbandry practices Poor fertility including acidity (surface and subsurface) High cost of inputs.

3. Introduction cont’d Use of lime and manure can address the constraints Spot application of the two resources would maximize their beneficial effects However, there has been no scientifically tested spot application method of lime in combination with manure as practised in Conservation Agriculture (CA) systems in Zambia today. Smallholder farmers mix lime and manure in the planting basins.

4. Introduction cont’d Objective: To identify an effective spot-placement method of manure and lime in combination for effective translocation of lime. Hypotheses: (a) placing OM over lime would ease movement of lime to address subsoil acidity; (b) Mixing of lime and OM would restrict movement of lime because of interaction between the two resources.

5. Materials and methods An Acrisol from Region III used Five months compost employed. 13.75kg soil in 1m columns used. Treatments added to the top 20 cm. 30 g lime and 60 g compost used. Blanket basal fertilizer (5g) at planting. Columns watered twice daily with up to 500 ml of deionized water for 12 weeks. Plants cut, chopped & placed in tussel bags and fresh sample weights taken. Dried in an oven at 70 0 C for 72 hrs and dry sample weights taken. The soil column was divided into 0-10, 10-20, 20-40, 40-60 and 60-80 portions and chemical parameters determined.

6. Treatments Treatment descriptionTreatment category Trt Code Lime bottom and compost TopPlacement treatmentLB+CT Compost Bottom and Lime TopPlacement treatmentCB+LT Lime, Compost and soil mixturePlacement treatmentLCSMix Compost and soil mixture – Compost CheckCheck - CompostCSMix Lime and soil mixture – Lime CheckCheck - Lime LSMix 0 Lime and 0 Compost - ControlControl0L0C The test soil had a marginal pH (5.4 in H 2 O), low in Ca (100 ppm), K (25 ppm) and OC (0.89%) while had adequate levels of Mg (140 ppm) and Phosphorus (23ppm). The compost manure had 390 and 240 ppm Ca and Mg respectively. Lime used is dolomitic with a neutralizing value (NV) of 100 % and 47.7% CaCO 3 and 40.1% MgCO 3 equivalents.

7. Results and discussion Treatment description Code Dry Matter Yield (g/plant) Root Yield (g/plant) Lime bottom and compost Top LB+CT2511 Compost Bottom and Lime Top CB+LT3914 Lime, Compost and soil mixture LCSMix2511 Compost and soil mixture – Compost Check CSMix288 Lime and soil mixture – Lime Check LSMix510 0 Lime and 0 Compost - Control 0L0C105 Lsd 0.05 7.71.0 Cv (%) 19.66.8 Shoot and root biomass following application of different placement treatments

8. Results and discussion cont’d Interaction between placement treatment and depth on pH response

9. Results and discussion cont’d Placement of lime overlying compost (CB+LT) treatment gave 35% more shoot biomass yield than the other placement treatments, contrary to what was expected Placement of lime overlying compost (CB+LT) recorded the largest increase in pH at subsurface soil level, 60-80 cm column depth with 1.35 pH units rise attributable to lime. This probably explains the high dry matter yield reported above as the root system was able to explore a larger soil volume. Conversely, placement of compost overlying lime and mixture treatments had highest pH at 0-20 cm and less so beyond, suggesting negative influence of the lime on the mobility of the alkalinity from the compost as it percolates through the limed portion of the column.

10. Results and discussion cont’d This suggests that direct contact of lime with OM, either solid or in solution through the labile organic colloids has no direct positive influence on the movement of the lime. This could be attributable to flocculation of the colloidal particles on the lime surface (Sparks, 1995). The liquid phase of OM has been demonstrated to be more effective in ameliorating soil acidity than the solid phase, (Butterly et al. 2013; Sakala et al., 2004; 2008). The soil being a variable charge, however, charge will also increase following the increase in pH (Nkhalamba, et al., 2003). Lime being less soluble, will form an active surface for ready flocculation of the available ions in the solubilised OM.

11. Results and discussion cont’d It would be logical to argue that a Zambian smallholder farmer would get a maize grain yield increase of up to 35% by separating lime and manure in spot application, with the organic resource placed below the lime, compared to mixing the two resources as is the practice now.

12. Conclusions Placement of lime overlying compost (CB+LT) has been found to be the best spot placement method for surface applied lime for effective translocation of the lime by compost to correct subsoil acidity. Flocculation was identified as the main mechanism attributable to the reduced translocation of lime to the subsurface column layers.