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Nutrient Balances in Farming Systems. Henry Ssali Kawanda, National agricultural Research Organisation [NARO]. Uganda Soils. Most are old/Highly weathered with little mineral nutrient reserves Rely on Soil organic matter [SOM] for nutrients and good physical properties

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Nutrient Balances in Farming Systems

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Nutrient Balances in Farming Systems

Henry Ssali

Kawanda, National agricultural Research Organisation [NARO]

Uganda Soils

  • Most are old/Highly weathered with little mineral nutrient reserves

  • Rely on Soil organic matter [SOM] for nutrients and good physical properties

  • SOM still the best indicator of soil fertility


  • SOM & nutrients decrease during cropping phase

  • Inputs [org and inorg] during cropping phase help maintain SOM/nutrients at higher levels

  • With grass/improved fallows, nutrients in the topsoil are replenished [recycling, BNF, depositions, transfer]

  • Soil analysis gives you the nutrient status of a plot at one given time

  • In addition, need to know the nutrient stocks and what is happening to them relative to various activities/operations on a plot & the entire farm


Farm usually has a number components/units

  • Crops [annual, perennial, high value etc]

  • Livestock

  • Pastures

  • Household [including surrounding plots]

  • Others

Nutrient flows/balances

Since soil productivity is dynamic, understanding flows and balances within a component and across components helps indicate

  • Extent of nutrient accumulation/depletion [mining]

  • Identify the major nutrient flows and

  • What is likely to happen in future [sustainability—at plot, farm, district, system, region or national level]


INcpsflows to CPS from outside the farm

OUTcpsflows out of CPS and the farm

INapsflows to APS from outside the farm

OUTapsflow out of APS and the farm

INhhsflows to HHS from outside the farm

OUThhsflows out of HHS and the farm

INTflowsflows between components on farm

Nutrient inputs

IN 1mineral fertilizers

IN 2organic inputs

IN 3atm deposition [rain, dust]

IN 4BNF [symbiotic & non-symbio]

IN 5Sedimentation [flooding/irrig]

IN 6subsoil exploitation [trees, etc]

Nutrient outputs

OUT 1harvest leaving farm [cps, aps, etc]

OUT 2crop residues/manure leaving farm

OUT 3leaching below root zone

OUT 4 gaseous losses [den, volat, burn]

OUT 5 runoff and erosion

OUT 6consption ending in deep latrines

Nutrient flows/balances in Uganda

  • The 1st was based on yield and input records coupled with generalized estimates of erosion and other processes as part of a SSA study [Stoorvogel & Smaling 1990]

  • Others have been more localised [e.g. Pallisa, Mpigi, Iganga & Kamuli (Wortmann & Kaizzi,1998); Mayuge (Esilaba et al 2002)


Farming systems

Balances and LUTs

  • Balances generally –ve; INs [BNF> Dep], OUTs [eros> harvests> leaching];

  • Annual crops largest area; balance more -ve cf perennials [land disturbance, low input use and poor soil cover], K problem for sold bananas w/o mulch,

  • -ve balances increase with yields and access to markets

  • Since yields are still low, LEISA [land husbandry, FYM, lcc, residue mangmt, etc] can reduce/maintain balances to near zero

Who mines most?

Policies for land management & subsequent pgms

  • Collected data from randomly selected HH

  • Provided an opportunity to understand

    • how farmers are managing their farms in the different AEZs

    • What the nutrient balances are over most of the country

    • Sustainability implications as farmers increasingly produce for the market

Status 1

  • Over 1300 plots with sufficient soils and socioeconomic data to estimate flows and balances

  • Have made initial runs and are currently examining data/assumptions/protocols for errors

Status 2

  • When this is complete will run data for the country [plot , farm level]

  • Data can be linked to other spatial information collected [AEZs, development domains, production zones, etc]

  • Early/rough indications:

    • farming in Ug is characterized by nutrient mining at the plot level; mining; mining in annuals > perennial; erosion and crop removal main culprits

    • Nutrient stocks vary with LUTs & AEZs

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