Potassium guidelines for maize: Fertasa 27 July 2016 Dr. Erik - - PowerPoint PPT Presentation

Potassium guidelines for maize: Fertasa 27 July 2016

• Dr. Erik Adriaanse

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Topsoil threshold values 80 and 120 mg K/kg 120 mg K/kg > 25 % clay - Based on Research at 53% clay with low subsoil reserves: K-applications = 0 – 156 kg/ha 80 mg K/kg < 25% clay – Based on assumption that sandy soils contain higher utilizable K-reserves in the subsoil: K-applications = 0 – 100 kg/ha Yield potential 2 – 12 t/ha Basis of recommendations in tables is not clear.

Previous FSSA potassium (K) guidelines for maize

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K in topsoil (Am Acetate; mg/kg) Sufficiency (%) K- recommendation (kg/ha) <40 <50% 134-179 41-80 50-70 90-134 81-120 70-90 45-90 121-160 90-100 0-45 >160 100

International topsoil K-norms for maize

Havlin, Beaton, Tisdale & Nelson, 1999

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120 mg K/kg (0-200 mm) if subsoil K reserves are low (<20 mg/kg) 80 mg K/kg (0-200 mm) if subsoil K reserves are high (>20 mg/kg) Yield potential 2 – 9 t/ha band place; slow build up Yield potential 7 - 20 t/ha band placed and broadcast; fast build up Basis of recommendations: Build up to thresholds as soon as economically justifiable and maintain

New Fertasa K-guidelines for maize

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Topsoil K-analysis (mg/kg) K-requirement (kg/ha) Subsoil high in K (>20 mg/kg) Subsoil low in K (<20 mg/kg) <20 175 330 20-40 125 270 41-60 75 210 61-80 25 150 81-100 90 101-120 30 >121 Shortcoming: May result in over-fertilisation when subsoil > 20 mg K/kg

K-requirement (kg/ha) for maize based on topsoil K-analyses (0-200 mm; Ammonium Acetate) to rectify deficiencies in soils with high and low subsoil K reserves.

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New Fertasa (kg K/ton) Prev. FSSA (kg K/ton)

Grain IFA (1992)a 4.1 IFA (1992)b 3.8 3.5 Average 4.0 Whole plant IFA (1992)a Barber & Olson (1968 20.5 IFA (1992)b Aldrich et al (1986) 16.0 Brazilian Oxisol (Fageira, Baligar & Jones, 2011) 23.0 Average 19.8 20.0 Removal of K/ton of maize grain - to be used for build up and maintenance of soil levels

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Applying more K than removal results in over fertilization and visa versa

Relationship between maize yield and K removed

K-removed (kg) Maize yield (ton)

50 100 150 200 250 300 350 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Plant + grain (kg) Grain (kg)

More K applied than removed in grain Less K applied than removed in grain

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K-analysis Yield Target (ton/ha) (mg/kg) 2 3 4 5 6 7 8 9 Subsoil high in K <20 18 23 28 33 38 43 48 53 20-40 16 21 26 31 36 41 46 51 41-60 14 19 24 29 34 39 44 49 61-80 12 17 22 27 32 37 42 47 81-100 10 15 20 25 30 35 40 45 >100 Subsoil low in K <20 25 30 35 40 45 50 55 60 20-40 23 28 33 38 43 48 53 58 41-60 20 25 30 35 40 45 50 55 61-80 18 23 28 33 38 43 48 53 81-100 15 20 25 30 35 40 45 50 101-120 13 18 23 28 33 38 43 48 121-140 10 15 20 25 30 35 40 45 >140

Shortcoming: May result in over-fertilisation when sub soils > 20 mg K/kg

K-recommendations (kg K/ha) for band placement at planting based on exchangeable K (Ammonium Acetate) in the topsoil (0-200 mm) for maize yields between 2 and 9 ton/ha .

Maximum K to be band placed at row widths of 0.76 m and narrower is 50 kg K/ha

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K-analysis Yield Target (ton/ha) (mg/kg) 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Subsoil high in K <20 210 215 220 225 230 235 240 245 250 255 260 265 270 275 20-40 160 165 170 175 180 185 190 195 200 205 210 215 220 225 41-60 110 115 120 125 130 135 140 145 150 155 160 165 170 175 61-80 60 65 70 75 80 85 90 95 100 105 110 115 120 125 81-100 35 40 45 50 55 60 65 70 75 80 85 90 95 100 >100 Subsoil low in K <20 365 370 375 380 385 390 395 400 405 410 415 420 425 430 20-40 305 310 315 320 325 330 335 340 345 350 355 360 365 370 41-60 245 250 255 260 265 270 275 280 285 290 295 300 305 310 61-80 185 190 195 200 205 210 215 220 225 230 235 240 245 250 81-100 125 130 135 140 145 150 155 160 165 170 175 180 185 190 101-120 65 70 75 80 85 90 95 100 105 110 115 120 125 130 121-140 35 40 45 50 55 60 65 70 75 80 85 90 95 100 >140 Shortcoming: May result in over-fertilisation when sub soils > 20 mg K/kg

K-recommendations (kg K/ha) for broadcast applications before planting and band placement at planting based on exchangeable K (Ammonium Acetate) in the topsoil (0-200 mm) for maize yields between 7 and 20 ton/ha .

Maximum K to be band placed at row widths of 0.76 m and narrower is 50 kg K/ha

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120 mg K/kg (0-200 mm) if subsoil K reserves are < 20 mg/kg – based on research 80 mg K/kg (0-200 mm) if subsoil K reserves are > 20 mg/kg and utilised – based on an assumption - May result in over fertilization of K

Critique on old and New Fertasa K-guidelines for maize

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K-calibration studies for maize: 0- 600 mm

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Exchangeable soil K (Ambic, 0-150 mm) vs relative maize yield on a clay soil (52% clay) - Cedara

Cmolc K/litre 0.1 0.2 0.3 0.4 0.5 0.6 mg K/litre 39 78 117 156 195 243 kg K/ ha 59 117 176 234 293 365

Farina, Channon , Thibaud, Phipson, 1992

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Depth (mm) Clay (%) Concentration (mg/kg) Quantity (kg/ha) 0 - 15 53 125 188 15 -30 53 24 36 30 - 45 53 20 30 45 – 60 49 16 24 Average = 52 Average = 46 Total = 278

Maize threshold value for exchangeable K over depths - Cedara

Farina, Channon , Thibaud, Phipson, 1992 Before commencement Optimum over 7 years

Shortcoming: Annual K analysis for deeper soil layers

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20 40 60 80 100 120 100 200 300 400 500 600 700 800

Exchangeable soil K (Ambic; 0- 600 mm) vs relative maize yield on a sandy soil (8.8% clay) - Balmoral

Relative Yield (%) Exchangeable soil K (kg/ha)

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Exchangeable soil K (Ambic; 0- 600 mm) vs relative maize yield over three localities – Vierfontein, Balmoral, Dirkiesdorp

Exchangeable soil K (kg/ha) Relative Yield (%)

10 20 30 40 50 60 70 80 90 100 110 100 200 300 400 500 600 700 800

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Cedara : 90% Balmoral: 31% Vierfontein: 13% Dirkiesdorp: 10%

Maize yield responses below K-threshold of 300 kg/ha; 0 – 600 mm

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Exchangeable soil K threshold for maize of 300 kg/ha; 0-600 mm, related to K concentrations

Soil Density (g/cm3) 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 0 - 600 mm (mg N/kg) 56 50 45 42 38 36 33 31 29 NB: This will only apply if the subsoil is well utilized: Not compacted Not acidic Not saline or sodic Not waterlogged

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Dry land and irrigation threshold = 300 kg K/ha; 0 - 600 mm. K-requirement factor (KRF) = K required to increase exchangeable K in soil with 1 kg/ha = 1.5 kg K/ha K-recommendation (kg/ha) = (300 – K exchangeable K in soil; 0-600 mm) x 1.5 Economic justification should be checked.

Management of exchangeable K-levels in the soil profile

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Before planting: broadcast and soil incorporated At planting: Maximum K to be band placed 50 mm x 50 mm from the seed After planting: Recommended when subsoil K is poorly utilized K should preferably be band placed but can be broadcast

Timing of K applications for maize

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Depth Increments: 0 – 200 mm 200 – 600 mm 0 – 600 mm Analysis: Extractant – Ammonium Acetate / Ambic

Soil Sampling for Potassium

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Topsoil (0 – 200 mm) threshold = 80 mg/kg with high subsoil reserves (> 20 mg/kg) Low and uncertain production potential (2 – 9 ton/ha) – band place slightly more than expected removal over a long period to reach threshold – maintain. Topsoil (0 – 200 mm) threshold = 120 mg/kg with low subsoil reserves (< 20 mg/kg) High and more certain production potential (7 – 20 ton/ha) – rectify threshold values by band placement and broadcast applications over a relatively short period – maintain. Profile (0 – 600 mm) threshold = 300 kg/ha = 29 – 56 mg/kg (1.7 - 0.9 g/cm3) Provided there are no physical or chemical restrictions in this part of the profile Check economic justification

New Fertasa potassium guidelines for maize - summary