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Soils & Fertilisers. Programme Soil Structure: Effect of soil management on soil structure Management strategies that can be used to improve or maintain the structure of a soil Soil Nutrient Status Determination of Fertiliser Requirements General Fertiliser Recommendations New technologies.
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Soils & Fertilisers Programme • Soil Structure: • Effect of soil management on soil structure • Management strategies that can be used to improve or maintain the structure of a soil • Soil Nutrient Status • Determination of Fertiliser Requirements • General Fertiliser Recommendations • New technologies
Introduction to soils Soils have a major influence on: • The human population - (global) • supplies food and clothing products
Challenge: Need to feed 9 billion people by 2050. FAO estimate this will require a 70% increase in food production: 80% to come from yield increases and 20% from area expansion World Population (in Billions): 1950-2050 Source: United Nations Population Division, World Population Prospects: The 2006 Revision.
Introduction to soils Soils have a major influence on: • The human population - (global) • supplies food and clothing products • filtering and purifying air and water • as a medium for waste disposal • fuel (biofuel) • New Zealand economy & employment
Plant requirements from soil • nutrients • physical support • water • oxygen Soil Structure: The formation and stability of soil structure depends mainly on : • organic matter • iron and aluminium oxides • clay and calcium/sodium Structure
The size, shape and stability of structure aggregates define the pore space. Large pores needed for drainage and small pores for water storage.
Effect of soil management on soil structure Cultivation temporarily increases macroporosity – aeration • can alsocause compaction, therefore decreasing macroporosity Continuous cultivation deceases structural stability, thereby: • increasing the risk of erosion • limiting crop emergence and water infiltration by formation of surface cap
Management strategies that can be used to improve or maintain the structure of a soil: • Pasture in rotation
Direct Drilling best on well drained, well structured soil Yields: variable but often similar to ploughing May depend on season, soil, management
Mulching and crop residue returns • Conserves organic matter (structural benefits) • Protects soil surface • Retains moisture • Reduces nutrient leaching losses • Less pollution Burning the preferred option?
Soil Nutrient Status Nutrient status depends on: • Soil parent material - different rock types contain different nutrient levels. • Clay & OM - store nutrients • Leaching & age - removal of nutrients • Anaerobic conditions (waterlogging) • Increased pH • Nutrient availability changes • Spring yellows
Managementstrategies • Pasture • Green manuring • Direct drilling • Crop residue management
Determination of Fertiliser Requirements • Soil Testing • Crop removal • Nutrient Budget
Soil Testing Soil pH (H2O) • 0-15 cm for cropping soils • OptimumpH(water) ranges of selected plants • Wheat 5.5 - 6.2 • Barley 5.9 - 6.5 • Oats 5.1 - 6.0 • Peas 5.9 - 6.5 • White clover 5.8 - 7.0 • Ryegrass 5.5 - 6.2 Amount of lime required to raise soil pH: = 26.2 - (4.4 × pH) + (0.07 × CEC) • Apply 1 tonne lime every 5 years to maintain soil pH
Nitrogen • Mineralisable N • Incubation study • Conditions artificial • 0 – 15 cm soil depth • Mineral N • Amount of NH4+ & NO3- • 0 – 15 cm or 0 – 60 cm sample • Determined in spring after winter leaching
Phosphorus • Olsen P • Calibrated for NZ conditions • Optimum value • Used to monitor soil fertility / Fertiliser inputs Potassium • Exchangeable K • QT units (MAF) or me/100g (cmolc/kg) • TBK • Reserve K for sedimentary soils • values > 0.5 very high
Nutrient Budget Fertiliser N required = (Crop N requirement – Soil mineral N) Fertiliser N inefficiency
General Fertiliser Recommendations Cereal crops NTending towards lowernitrogen inputs as per nutrient budget; wheat calculator. P Olsen P >15 sufficient Maintenance rates depend on crop removal Typical rates: K QT value of 6 – 10 adequate Maintenance rates depend on crop removal & reserve K levels.
S Sometimes the forgotten nutrient. Maize N High requirements. Use maize calculator. P Olsen P of 15 adequate. Maintenance depends on yield and product. K High removal if silage. Ash/Peat soils have low K reserves Micronutrients Iron & Zinc deficiencies possible
Ryegrass P & S Deficiencies likely if Olsen P <15 K Depends on residue management (removal) Clover P & K Avoid spring applications of P/K fertilisers Mo Essential for N fixation Boron Required for nectar sugar balance
Brassica crops High N & K requirements: • 150 – 170 kg N/ha • 75 – 200 kg K/ha Responses to sodium likely in Fodder Beet crops • 50 – 100 kg NaCl/ha Boron deficiencies common: • Apply 10 – 15 kg borate46/ha or 2L/ha BoroSolv Molybdenum deficiencies also common in Cabbage/Cauliflower crops (whiptail)
