Nutrient Balances in Farming Systems

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Nutrient Balances in Farming Systems

• Henry Ssali
• Ephraim Nkonya

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Introduction

• This presentation addresses USSPs objective
  related to NRM and sustainable agriculture.
• The results of this research discuss some of the
  reasons that have contributed to sluggish
  agricultural growth
• The results also demonstrate that for the
  agricultural sector to have a sustainable growth
  discussed previously, a combination of soil
  fertility practices, improved crop varieties and
  the accompanying institutions services are
  required

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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

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SOIL MANAGEMENT

• SOM, nutrients yields decrease with time during
  cropping phase
• Inputs org and inorg during cropping phase help
  maintain SOM/nutrients/yields at higher levels
• With grass/improved fallows, nutrients in the
  topsoil are replenished recycling, BNF,
  depositions, transfer

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Long-term impact of soil nutrient depletion on
crop yield
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Profit with without fertilizer agroforestry,
Embu Kenya
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Soil analysis

• 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 with time relative to
  various activities/operations at plot, farm
  higher levels

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FARM COMPONENTS

• Farm usually has a number of components/units
• Crops annual, perennial, high value etc
• Livestock
• Pastures
• Household including surrounding plots
• Others
• NUTRIENTS flow within, between outside these
  components/units

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Nutrient flows/balances

• Since soil productivity is dynamic, understanding
  nutrient flows and balances helps indicate
• Extent of nutrient accumulation/depletion
  mining
• Identify the major nutrient flows and
• What is likely to happen in future
  sustainabilityat plot, farm, district, system,
  region or national level

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Nutrient inputs Ins

• IN 1 mineral fertilizers
• IN 2 organic inputs
• IN 3 atm deposition rain, dust
• IN 4 BNF symbiotic non-symbio
• IN 5 Sedimentation flooding/irrig
• IN 6 subsoil exploitation trees, etc

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Nutrient outputs OUTs

• OUT 1 harvest leaving farm cps, aps, etc
• OUT 2 crop residues/manure leaving farm
• OUT 3 leaching below root zone
• OUT 4 gaseous losses den, volat, burn
• OUT 5 runoff and erosion
• OUT 6 consption ending in deep latrines

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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)

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Generalized
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Farming systems
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Detailed/who mines most?
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Earlier Findings

• Balances generally ve INs BNFgt Dep, OUTs
  erosgt harvestsgt leaching eros mainly
  backslopes and summits
• Annual crops largest area with more mining cf
  perennials land disturbance, low input use
  poor soil cover, K problem where bananas are
  sold or w/o mulch

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Earlier Findings 2

• Mining increases with yields and produce sales
• good managers tend to mine more
• Since yields are still low, LEISA land
  husbandry, FYM, lcc, residue mangmt, etc can
  reduce/maintain balances to near zero

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Policies for land management Project

• Collected data from 147 randomly selected
  communities
• 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

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Data collected/selected

• Crop type, yield, destination sold/eaten
• plot type, sizes, slope, land crop residue
  management
• inputs types, sources, rates
• Surface soil sample fertility status/stocks/textu
  re
• Livestock types, number, grazing time where
  on/off farm, feeds
• 1717 plots 409 hh with sufficient soils, plot
  socioeconomic data to estimate nutrient flows
  balances

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Soils LUT, location
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Nutrient balances
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Major nutrient inflows outflowsplot level
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Notes

• Data can be linked to other spatial information
  collected AEZs, development domains, production
  zones, etc
• Nutrient stocks vary with LUTs AEZs but
  basically proportional to SOM sandy soils with
  low SOM Nakasongola, West Nile, L. Kyoga basin
  also have low stocks

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Balances stocks
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Opportunities

• Since yields are still low and farms are small,
  mining can substantially be reduced through
  integrated approaches that incorporate basically
  LEISA
• Reducing losses thru erosion only 27 plots used
  practiceswater mngmt/harvest, CA
• Incorporate legumes into fallows, pastures crop
  rotations to increase BNF
• Deliberate use of available nutrient sources
• hh/crop residuesdistributed vs dumping,
• animal manure only 16.4 yet 55 had more than 1
  TLU5.7 kg N/ha

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EPHRAIM
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Economic impact of soil nutrient depletion

• Biophysical results show the high dependency of
  farmers on soil mining for their livelihoods
• Approx 25 of farm household income has to be
  spent to replenish depleted nutrients
• Richer farmers or those realizing higher profits
  deplete their soil more severely than those with
  lower income or profit
• However, those realizing higher profits are in
  more fertile areas whose soils can support such
  depletion for much longer time than those in poor
  soils

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Economic impact of soil nutrient depletion
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What can be done to redress the soil nutrient
depletion?

• Inorganic fertilizer?
• High fertilizer price partly responsible for
  limited use of inorganic fertilizer.
• The marginal value/cost ratio (VCR) of fertilizer
  is 0.31.
• A VCR of 1.0 is required for fertilizer to be
  profitable
• A VCR of at least 2.0 is required for widespread
  adoption of fertilizer (CIMMYT, 1985)

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What can be done to redress depletion? (2)

• Most likely solution lies in
• Integrated soil fertility management
• Use of improved seeds
• Improved markets and other agricultural services
• However, profitability of soil fertility
  management practices to complement inorganic
  fertilizer not well known

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Future research

• Profitability of alternative soil fertility
  management practices that could complement
  inorganic fertilizer
• Why farmers do not adopt some cheap alternative
  soil fertility practices, e.g. management and use
  of organic fertilizers
• Investigate innovative options for making
  fertilizer more profitable. For example
• Sasakawa Global 2000 demonstration plots showed
  high profit of fertilizer use. Is it because the
  plots used a combination of inputs that
  smallholder farmers dont?
• Marketing options that could be considered to
  lower the transaction costs of fertilizer
  marketing