Soil Acidity: sustainability of living i on the edge

Transcription

1 Soil Acidity: sustainability of living i on the edge This talk: Underlying concepts Concerns Some noteworthy SASRI research findings A change in philosophy? 1

2 Underlying concepts Plants are able to survive at much lower ph s in nutrient solution than in soils. Why? 2

3 Variation in exchangeable aluminium with soil ph Al + lime ph (water) Variation in exchangeable aluminium with ph in a Cartref soil Al ppm Soil ph water 3

4 The harmful effect of Al on root growth and performance is mitigated by increases in levels of basic cations (Ca & Mg) Al saturation Al Al sat % = Ca + Mg + K + Al X 100 4

5 The spectrum of factors restricting growth on acidic soils: Al toxicity Deficiencies of Ca and Mg Deficiencies of Zn and Mo Acid subsoils: a chemical barrier to root growth (moisture and nutrient availability restricted) Relative sensitivity to soil acidity of crop and vegetable species highly sensitive moderately sensitive moderately tolerant highly tolerant carrot, cabbage, tomato lucerne, clovers sunflower, dry bean cotton, barley, dolichos beans sorghum, buckwheat, babala, teff soyabean maize, lupin, velvet beans, sunn hemp potato oats sweet potato cow peas, Eragrostis curvula 5

6 Relative sensitivity to soil acidity of crop and vegetable species highly sensitive moderately sensitive moderately tolerant highly tolerant carrot, cabbage, tomato lucerne, clovers sunflower, dry bean cotton, barley, dolichos beans sorghum, buckwheat, babala, teff soyabean maize, lupin, velvet beans, sunn hemp potato oats sweet potato cow peas, Eragrostis curvula SUGAR CANE Relative sensitivity to soil acidity of crop and vegetable species highly sensitive moderately sensitive moderately tolerant highly tolerant carrot, cabbage, tomato lucerne, clovers sunflower, dry bean cotton, barley, dolichos beans sorghum, buckwheat, babala, teff soyabean maize, lupin, velvet beans, sunn hemp potato oats sweet potato cow peas, Eragrostis curvula SUGAR CANE 6

7 Current soil criteria for liming Al sat < % for N12 Al sat < % for other varieties 1 Effects of soil aluminium saturation on the yields of cane varieties Yield % Nx N Soil Al sat % 7

8 Current soil criteria for liming Al sat < % for N12 Al sat < % for other varieties >0 ppm Ca in topsoil > 25 ppm Mg 1 to 3 t lime/ha for soil health (ph <5) CONCERNS Pervasive Al toxicity in coastal areas, Zululand and Midlands Widespread nutrient deficiencies (Ca, Mg) Re acidification 8

9 300 ppm Australia 0 ppm FAS Kingston & Aitken, 1996 Calcium status of topsoil samples submitted to FAS (05 07) Extension Sub Region Percentage < 0 ppm < 100 ppm Zululand Central Durban North Coast Lower South hcoast Acknowledgement: Rod Harding 9

10 0 ppm Kingston & Aitken, 1996 Calcium (and Mg and K) levels in subsoils severely deficient in many Industry soils, suggesting mining of subsoil reserves. 10

11 Re-acidification Re acidification: major causes Crop removals of Ca and Mg Acidification by N fertilizers 11

12 Rates of re acidification SASRI research findings Annual ph decline of 0.1 unit for fields on Zululand l estate tt (Schroeder, Robinson, Wallace & Turner, 1994) Annual ph decline of 0.2 units on a medium buffered soil (Schumann, 1999) Al saturation increased dfrom 5 to 30% in 5 years on a Nomanci soil at Paddock (Nixon, Meyer, McArthur & Schumann, 03) Variation in exchangeable aluminium with ph in a Cartref soil Al ppm years Soil ph water 12

13 1 100 Effects of soil aluminium saturation on the yield of variety N12 Plant Yield % 80 Ratoon Soil Al sat % Are we adequately accommodating re-acidification in our current recommendations? 13

14 Research findings Impact of lime and gypsum on sugarcane yields. Nixon, Meyer, McArthur & Schumann, 03 14

15 75 70 Responses to lime and gypsum at Dalton (Magwa soil, clay = 59%, ph w = 4.2, 84% ASI) P + 4R ts/ha 65 N12 N L / G (t/ha) 37 Lime response of N12 at Dalton (Magwa soil; 59% clay, ph 4.2, AS = 84%) 37 Lime response of N16 at Dalton (Magwa soil; 59% clay, ph 4.2, AS = 84%) 2R+3R+4R? Sucrose (t/h ha) R+3R+4R P + 1R Sucrose (t/h ha) P + 1R Lime (t/ha) Lime (t/ha) 15

16 80 Responses to lime at Paddock (Nomanci soil, clay = 26%, ph w = 4.4, 80% ASI) 75 ts/ha Total: P + 5R N12 N16 NCo lime t/ha 32 Lime response of N12 at Paddock (Nomanci soil; 26% clay; ph 4.4) 32 Lime response of N16 at Paddock (Nomanci soil; 26% clay; ph 4.4) Sucrose (t/ha) 24 P + 1R 2R + 3R 4R + 5R Sucrose (t/ha) 24 P + 1R 2R + 3R 4R + 5R Dolomitic lime (t/ha) Dolomitic lime (t/ha) 30 Lime response of NCo376 at Paddock (Nomanci soil; 26% clay; ph 4.4)? Sucrose (t/ha) P + 1R 2R + 3R 4R + 5R Dolomitic lime (t/ha) 16

17 Salient findings from these trials Massive varietal differences. Massive differences in responses between plant / early ratoons and later ratoons. Cause re acidification? A h i hil h A change in philosophy in dealing with the soil acidity problem? 17

18 Soil acidity correction for N12 on a loam soil SOIL TEST ph water Al sat % RECOMMENDATION Target Al sat % Lime (t/ha) MANAGEMENT OF SOIL ACIDITY FOR N12 80 Soi il Al saturation % 4 t lime/ha 0 R 7 P R 1 R 2 R 3 R 4 R 5 R 6 R 7 R 8 Crop 18

19 MANAGEMENT OF SOIL ACIDITY FOR N12 80 il Al saturation % So 4 t lime/ha Yield loss? 0 R 7 P R 1 R 2 R 3 R 4 R 5 R 6 R 7 R 8 Crop MANAGEMENT OF SOIL ACIDITY FOR N12 80 Soi il Al saturation % 4 t lime 4 t lime 4 t lime 0 7 P P P Crop 19

20 Soil acidity correction for N12 on a loam soil SOIL TEST ph water Al sat % RECOMMENDATION Target Al sat % Lime (t/ha) MANAGEMENT OF SOIL ACIDITY FOR N12 80 il Al saturation % So 4 t lime/ha 10 t lime/ha Yield loss? 0 R 7 P R 1 R 2 R 3 R 4 R 5 R 6 R 7 R 8 Crop

21 MANAGEMENT OF SOIL ACIDITY FOR N12 80 So oil Al saturation % 4 t lime 4 t lime 4 t lime 10 t lime 5 t lime 5 t lime 0 7 P P P Crop Variation in exchangeable aluminium with ph in a Cartref soil Al ppm uneconomic Soil ph water 21

22 1 Effects of soil aluminium saturation on the yield of variety N Yield % Soil Al sat % CONCLUSIONS Soil acidity and Ca deficiency serious growth limitations in large areas of the Industry. Major varietal differences in terms of tolerances to soil acidity factors. Increased response to lime in later ratoons appears to be due to re acidification. SASRI research findings indicate a need for lime recommendation criteria to be modified to accommodate re acidification. 22