Reference Materials Module 3

Transcription

1 SWEET POTATO NUTRIENT REQUIREMENTS Reference Materials Module 3 Prepared by A. Noguera-Ramkissoon, Training Coordinator based on the presentation developed by Anthony Seesahai, Project Consultant 29/10/11

2 GENERAL ASPECTS TOLERATES ACID, INFERTILE SOILS WHEN GROWN ON SLOPING LAND, EROSION CAN DEPLETE THE SOILS OF NUTRIENTS AND TOP SOIL NEED TO IMPROVE SOIL CONSERVATION PRACTICES AND NUTRIENT APPLICATIONS TO ENHANCE SOIL CHEMICAL AND PHYSICAL CHARACTERISTICS, OFFER THE CURRENT CROP PROPER NUTRITION, AND ENSURE GOOD NUTRIENTS FOR THE FOLLOWING CROP DEFINITIONS SUFFICIENCY: THERE IS ENOUGH FERTILISER IN THE SOIL FOR THE PLANT TO GROW AND PRODUCE A GOOD CROP DEFICIENCY: THERE IS NOT ENOUGH FERTILISER IN THE SOIL FOR THE PLANT TO GROW AND PRODUCE A GOOD CROP. CRITICAL LEVEL: THE AMOUNT OF FERTILISER IN THE SOIL AND THE MINIMUM AMOUNT NEEDED TO BE ADDED TO REACH SUFFICIENCY LEVEL. THIS DEPENDS UPON THE AMOUNT OF NUTRIENTS REMOVED BY THE CROP. 1

3 NUTRIENT REMOVAL BY THE SWEET POTATO PLANT FERTLISER USE NO FERTILIZATION THE FARMER FERTLISES BUT DOES NOT KNOW HOW MUCH NUTRIENTS THE SOIL HAS- TOO LITTLE OR TOO MUCH FERTILISER OR THE WRONG TYPE MAINTENANCE FERTILISER: REPLACE NUTRIENTS REMOVED BY THE CROP WITHOUT CHANGING THE SOIL NUTRIENT LEVELS BUILD FERTILISER: USING EXCESS FERTILISER TO BUILD THE NUTRIENT LEVELS OF THE SOIL FOR ANOTHER CROP: IMPORTANT IN CONTINUOUS MONOCROPPING SYSTEMS WHAT IS AN ESSENTIAL ELEMENT? THE PLANT CANNOT COMPLETE ITS GROWTH CYCLE WITHOUT IT THE ROLE THE NUTRIENT PLAYS CANNOT BE REPLACED BY ANOTHER NUTRIENT THE NUTRIENT IS DIRECTLY INVOLVED IN THE PLANT S GROWTH AND REPRODUCTION MOST PLANTS NEED THIS NUTRIENT TO SURVIVE 2

4 MOBILE AND IMMOBILE NUTRIENTS WITHIN A PLANT AND SOIL PLANT: MOBILE NUTRIENTS WITHIN A PLANT: NITROGEN, PHOSPHORUS, POTASSIUM, MAGNESIUM, MOLYBDNEUM, CHLORIDE. SOIL:(MOBILE): SULPHATE, NITRATE,CHLORIDE, BORATE. IMMOBILE NUTRIENTS IN PLANT: BORON, CALCIUM, COPPER, IRON, MANGANESE, NICKEL, SULPHUR, ZINC. RELATIVELY IMMOBILE IN SOIL: AMMONIUM, CALCIUM, COPPER,IRON, MAGNESIUM, MANGANESE, MOLYBDENUM, NICKEL, POTASSIUM, PHOSPHATE, ZINC. SOIL FERTILITY TEXTURE: CLAY. CLAY HOLDS PLENTY WATER AND NUTRIENTS. SAND: WATER DRAINS OUT QUICKLY. ORGANIC MATTER: HAS A HIGH CEC. ph: THE SOIL S ACIDITY OR H ion CONCENTRATION. CATION EXCHANGE CAPACITY:THE ABILITY OF A SOIL TO RETAIN AND SUPPLY NUTRIENTS TO A CROP. THE CEC OF THE SOIL REGULATES NUTRIENT ABSORPTION Negatively charged soil particles affect the absorption of mineral nutrients Cation exchange occurs on the surface of the soil particle Cations (+ve charged ions) bind to soil as it is ve charded If potassium binds to the soil it can displace calcium from the soil particle and make it available for uptake by the root 3

5 THE SOIL ph AFFECTS NUTRIENT RELEASE AND ABSORPTION ph affects the growth of plant roots and soil microbes Root growth favors a ph of 5.5 to 6.5 Acidic conditions weathers rock and releases potassium, magnesium, calcium, and manganese. The decomposition of organic material lowers soil ph. Rainfall leaches ions through soil to form alkaline conditions SOIL TESTS ARE VERY IMPORTANT AND IT HELPS TO DETERMINE THE RECOMMENDED FERTILIZER SOIL TESTING SERVICES 4

6 SOIL FERTITLITY Sweet potato production can be improved if soil acidity is lowered which can be achieved by applying limestone. In sandy soils leaching is high and therefore requires frequent liming. Contact your County Extension Office to get a soil test done so that the exact limestone requirement and the type, rate and timing of fertilizer application will be known. SOIL FERTILITY IN TRINIDAD SOILS - Ways in which high soil acidity affects crop productivity directly: 1. Acidic soils have low calcium content which is essential for plant growth 2. High concentrations of aluminum, iron and manganese may be present in acidic soils that are toxic to plant growth. 3. In acidic soil bacteria may be unable to rapidly decompose organic matter. 4. Some herbicides are less effective. 5. Poor soil aeration and restricted permeability may result due to soils not being well aggregated. 5

7 SUMMARY SOIL NUTRIENT STATUS, NUTRIENT TYPE, SOIL TYPE, ph THE CEC ALL AFFECT THE AVAILABILITY OF NUTRIENTS TO THE CASSAVA PLANT THE IDEAL SOIL: CLAY LOAMS WITH HIGH ORGANIC MATTER. THE IDEAL ph : 5.5 RESEARCH FINDINGS ON THE SWEET POTATO PLANT SWEET POTATO ROOTS ARE VERY SENSITIVE TO LOW OXYGEN SUPPLY- WATERLOGGING, CLAY SOILS, RAPID WATER LOSS AND CAKING 6

8 A DYNAMIC RELATIONSHIP BETWEEN WATERLOGGING (SOIL DENITRIFICATION) AND POTASSIUM N/K RATIO IN SOIL IS IMPORTANT IN TUBER BULKING ORGANIC MATTER A STEADY SUPPLY OF NUTRIENTS AS THE ORGANIC MATTER DECOMPOSES IT PROVIDES A SUITABLE SUBSTRATE FOR HOLDING SOIL NUTRIENTS IN AN AVAILABLE FORM INCREASES WATER RETENTION AND SOIL TAKES LONGER TO DRY OUT GIVES THE SOIL AN OPEN TEXTURE SO MORE AIR CAN GET INTO THE ROOTS THE SWEET POTATO PLANT: GROWTH AND DEVELOPMENT: 1-6 WEEKS AFTER PLANTING (WAP) PHASE 1: GROWTH OF THE TERMINAL BUD, GROWTH OF THE AXILLARY BUDS RAPID LEAF GROWTH- NUMBER AND EXPANSION OF THE LEAF SURFACE RAPID GROUND COVER ROTORVATE 1 ton MANURE INTO SOIL. ADD RECOMMENDED RATE OF LIMESTONE TO GET THE ph TO THE SWEET POTATO PLANT: GROWTH AND DEVELOPMENT: 4-6 WEEKS AFTER PLANTING (WAP) THIN ANDTHICK ROOTS: BEGIN TO GROW AND DEVELOP AND FUNCTION IN WATER AND NUTRIENT ABSORPTION. TUBER ROOT: BEGIN 4-6 WAP. FARMER - THE FIRST FERTILISATION SHOULD BEGIN 4-6 WAP WHEN THE FIBROUS AND TUBER ROOTS ARE PRESENT AND THE TUBER ROOTS APPEAR. 7

9 THE SWEET POTATO PLANT: GROWTH AND DEVELOPMENT: 4-6 WEEKS AFTER PLANTING (WAP) (TUBER INITIATION) BASED ON THE SOIL TEST, ADD THE RECOMMENDED AMOUNT OF FERTILISER TO THE CROP + AN ADDITIONAL AMOUNT OF POTASH (BANDED ALONG THE ROW). OBSERVE THE GROWTH AND DEVELOPMENT OF THE CANOPY AND LOOK FOR NUTRIENT DEFECIENCY SYMPTOMS. THE SWEET POTATO PLANT: GROWTH AND DEVELOPMENT: 8-10 WEEKS AFTER PLANTING (WAP) (TUBER BULKING) EITHER WET SALT WITH POTASH OR BAND WITH POTASH. MAXIMUM CANOPY GROWTH AND HIGH LAI NUTRIENT DEFICIENCY SYMPTOMS IN SWEET POTATO: NITROGEN N def. symptoms common sandy soils, soils with low OM or waterlogged soils (denitrification by soil bacteria). Small, pale green, dull leaves, slow plant growth. Increase in red pigmentation on petioles and veins of young leaves, more visible on undersurface of leaf.. Uniform yellowing of old leaves, wilt and die. in 8

10 CORRECTION OF NITROGENT DEFICIENCY SYMPTOMS IN SWEET POTATO APPLY N-FERTILISERS AT PLANTING AND AT 6-8 WAP UREA, AMMONIUM SULPHATE, CALCIUM NITRATE (CHECK PRICE) ADD ORGANIC MATTER OR INTER PLANT WITHLEGUMINOUS PLANTS (MUNG) HIGH N RATES CAN REDUCE TUBER GROWTH NUTRIENT DEFICIENCY SYMPTOMS IN SWEET POTATO: PHOSPHORUS DIFFICULT TO DIAGNOSE- REDUCED PLANT GROWTH WITHOUT VISIBLE DEFECIENCY SYMPTOMS DARK, GREEN LEAVES REDDISH BROWN OR PURPLE PIGMENTATION ON OLDER LEAVES UNEVEN YELLOWING OF OLDER LEAVES CORRECTION OF PHOSPORUS DEFICIENCY IN SWEET POTATO APPLY SUPERPHOSPHATE OR NPK. LOW TO DISSOLVE AND HAS LOW SOIL MOBILITY, CAN APPLY AT PLANTING. APPLY AS A BAND OR SPOT RATHER THAN BROADCASTING NUTRIENT DEFICIENCY SYMPTOMS 9

11 IN SWEET POTATO: POTASSIUM COMMON ON SANDY SOILS. SP REQUIRES HIGH LEVELS OF K. LIGHT GREEN + INTERVEINAL CHOLOROSIS on MATURE LEAVES AT TUBER BULKING PHASE. OLDER LEAVES BECOME YELLOW, AROUND THE LEAF MARGIN AND THE YELLOW AREAS DIE CORRECTION OF PHOSPHOROUS DEFICIENCY SYMPTOMS IN SWEET POTATO ADD POTASSIUM SULPHATE OR POTASSIUM CHLORIDE AT 4-6 WAP. N/K RATIO = 1/5. Mg, B AND Fe DEFICIENCY Mg DEF. = PALE GREEN TO YELLOW INTERVEINAL CHLOROSIS. SLIGHTLY DROOPING LEAVES. BORON DEF. = SMALL, THICK, BRITTLE PUCKERED YOUNG LEAVES. Fe DEF. = YELLOW, ANAEMIC YOUNG LEAVES MAGNESIUM (Mg) DEFICIENCY 10

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