Integrated Soil Fertility Management in the Topics

Transcription

1 Integrated Soil Fertility Management in the Topics Prof. Dr. Anthony Whitbread Georg-August-University, Göttingen Crops and Productions Systems in the tropics Lecture

2 Outline of lecture Introduce the concept of integrated soil fertility management Outline some basic concepts of plant nutrition: Plant requirements Macro and micro nutrients Factors affecting nutrient availability Consequences of low nutrient availability or toxicity Sources of nutrients Organic sources Inorganic sources Managing nutrients in variable climates Small N application

3 Lecture 1, we covered the classification of tropical farming systems * where annual crops are a dominant/important component: 1. Shifting cultivation systems 2. Semi-intensive rainfed systems 3. Intensive rainfed systems 4. Irrigated and flooded systems 5. Mixed annual/perennial systems Cropping frequency increases Integrated nutrient management may play a role in all systems, but as cropping frequency increases, management is more precise. Note: Soil fertility management in: #1 shifting cultivation systems relies mainly on the bush fallow phase; #2 semi-intensive systems is generally low input with fallow phases (regenerating vegetation, grassland) sometimes used to restore soils. In both of these systems, the fallow periods become shorter as population pressure (people and animals) increase. * Norman M.J.T. (1979). Annual Cropping Systems in the Tropics. Gainesville, Florida: University Presses of Florida, 276 pp.

4 Integrated soil fertility management (ISFM): is the application of soil fertility management practices and the knowledge to adapt these to local conditions, which maximise fertiliser and organic resource use efficiency and crop productivity. These processes necessarily include appropriate fertiliser and organic input management in combination with the utilisation of improved germplasm. Source: Sanginga and Woomer (eds.) Integrated Soil Fertility Management in Africa: Principles, Practices and Developmental Process. TSBF- CIAT Nairobi: 263 pp. ( Also you can watch a short You Tube video from the African Soil Health Net work:

5 The factors affecting nutrient availability to plants Three factors are important in maintaining supply of nutrients in the soil solution in a plant available form: 1.Supply from the solid phase: (i)sorption or exchange surfaces (ii)slowly soluble salts (iii)organic matter. 2.Soil ph This lecture introduces these aspects in relation to integrated soil fertility management 3.Moisture supply

6 Nutrient limitation also results from: Leaching Soil erosion Removal of nutrients (exporting)

7 Nutrient deficiencies limit potential yield: Macronutrients N P K S Ca Mg Si Micronutrients B Cl Cu Zn Mn Fe Mo Ni Se Na Liebig s Barrel was the first attempt at a simplified concept of nutrients limiting yield. Justus von Liebig , credited with discovering N as a plant nutrient. The original nutrient limitation concept was developed by Carl Sprengel ( ) interestingly he worked in Göttingen

8 Tissue testing: Defining the relationship between nutrient concentration and yield This relationship is defined experimentally where increasing levels of nutrients are supplied to a deficient growing medium (e.g. sand) with the plant tissue nutrient concentration and maximum yield of a crop being measured.

9 1. Soil organic matter loss and soil fertility Reduces soil nutrient supply [i.e. mainly via lower capacity for the mineralisation of nutrients, decreases in cation exchange capacity (CEC)] Reduces soil physical fertility [i.e. a range of soil structural properties including aggregation, infiltration capacity, soil strength] Increases global CO 2 emissions to the atmosphere.

10 Soil fertility decline Figure adapted from: Dalal, RC. and Mayer, R.J Australian Journal of Soil 24(2)

11 2. ph Nutrient availability is closely related to soil ph this is a complex story, but a common graphical representation is given below. The optimal ph range for most plants is , however this varies by plant spp. e.g. barley tolerate ph ranges 6.5-8, rice Outside of these ph ranges, plant growth is less than optimal because nutrient availability is lower and or toxicities may affect root development and/or uptake.

12 Nutrient toxicity/deficiency and ph ph Water 1:5 Impacts Source: Constraints to cropping soils in the northern grains region-a decision tree GRDC Northern SSC program (Qld NR&W publication)

13 Some major effects of ph in the soil Source: Dierfolf, Fairhurst and Mutert (2001). Soil Fertility Kit: A toolbox for Acid, upland soils fertility management in Southeast Asia. Potash and Phosphate Institute. p.41

14 Acid Soil effects ph-acid SOILS Aluminium toxicity In Canola Impacts Al tolerant root tip Al sensitive root tip Major production losses occur when acidity increases to the point where toxic elements in the soil, such as aluminium and manganese, dissolve The aluminium damages root growth and restricts the ability of plants to take up nutrients Acid Soils-A ticking time bomb. CSIRO Plant Industry Information Sheet.

15 Toxicities ph-acid SOILS Manganese toxicity in Canola Manganese an essential element for plant growth but in small quantities Toxic when in excess Effects shoot growth Acid Soils-A ticking time bomb. CSIRO Plant Industry Information Sheet.

16 3. Soil moisture - Climate variability and implications for nutrient management In rainfed systems, timing of rainfall strongly influences the availability and potential response to applied nutrients. Soil moisture is needed to mineralise nutrients from soil organic matter, allow plant roots to penetrate soils and access nutrients (via diffusion or active uptake). Rainfall helps applied nutrients to enter the root zone, undergo chemical transformation (e.g.. urea hydrolysis) to plant available forms. The timing of rainfall is therefore critical for plant growth, nutrient availability and uptake and ultimately nutrient use efficiency. Because this is a complex system, crop and soil models coupled to long term weather data is used to understand the climate x soil x management interactions.

17 Maize yield Why do researchers use models? Yield N rate (kgn/ha) Experiments give different results in different seasons

18 Why do researchers use models? Grain yield (kg/ha) Rushinga Zvimba Ndabazinduna Gutu N applied (kg/ha) Experiments give different results in different locations

19 To deal with large temporal variability Impacts Chisepo seasonal rainfall variation Avg Season of harvest October to May rainfall (mm)

20 Key features of agricultural production system Climate Transpiration Flowering/grain production Management Establishment Runoff/ Erosion Leaf area / biomass production Evaporation Harvest Residue Manure Redistribution Root growth Decomposition/ Incorporation Soil water Water uptake Nutrient uptake Soil Organic Matter / Nutrients Drainage Leaching

21 Fertiliser response units are additional bags of grain for one bag of nitrogen fertiliser (15 kg N/ha) Sowing window from 1 Nov a 1 Dec b Plant population (/m2) 2.0 d 3.5 c Weed control good poor e good poor good poor good poor Soil Depth Soil fertility Shallow (50 cm) low mod high Medium (100 cm) low mod high Deep (>150 cm) low mod high very low risk (one year in 10) medium risk (one year in 5) high risk situations (>1 year in 5)

22 Sources of plant nutrients in agriculture 1. Parent material and soil organic matter a. Weathering of soil minerals eg. (PO 3+ 4 from Apatite) b. Mineralisation from soil organic matter (eg. NO3 - and NH4 +, SO 2-4 ) c. Input from the atmosphere (rainfall, sea spray, lightning, dust). 2. Organic sources a. Manures (farm yard manure FYM) b. Biological N fixation c. Composting, mulching, crop residue retention etc. 3. Inorganic sources a. Manufactured Chemical fertilisers 4. Mineral a. Rock phosphate b. Gypsum, Dolomite

23 Mineral contents of some common organic resources. Source: Sanginga and Woomer (eds.) Integrated Soil Fertility Management in Africa p. 219

24 Manufacture of common N fertilisers Source: Blair and Sale Plant Nutrition notes.

25 Manufacture of common N and P fertilisers Fertiliser P content (%) P solubility (%) Single super 9 80 Double super Triple super MAP DAP Ammonium polyphosphate Rock phosphate 20 0

26 Crops and Production Systems in the Tropics Recommended reading An example of extension material on application of N fertiliser to maize in Malawi and Zimbabwe: Sanginga and Woomer (eds.) Integrated Soil Fertility Management in Africa: Principles, Practices and Developmental Process. TSBF-CIAT Nairobi: p Chapters 1, 2 and 4. This is downloadable from: df Recommended viewing: