Soil and tissue testing in organic production

Soil and tissue testing in organic production

Soil testing : Understanding the soil test report is half the battle

.pdf available at http://vric.ucdavis.edu

Should soil test results for an organic field be interpreted differently than for a conventional one? Soil characteristic ph No Extractable P No Exchangeable K No Cation saturation No Micronutrients No Organic matter?? N status??

How does organic management change soil fertility characteristics? cover cropping affects mostly N availability parameters compost affects mostly P and K availability

Paired fields of Central Valley tomato growers : Grower Management system Organic matter (%) Total N (%) Olsen P (PPM) Exchangeable K (PPM) 1 organic 0.87 0.09 81 537 conventional 0.78 0.08 35 393 2 organic 1.12 0.12 52 682 conventional 1.04 0.11 42 470 3 organic 1.60 0.16 105 917 conventional 1.03 0.10 36 359 4 organic 1.30 0.13 38 315 conventional 1.30 0.13 15 240 Ave organic 1.22 0.12 69 613 conventional 1.04 0.10 32 365

What about nutrient balance? Theory : cation ratios can be manipulated to improve crop growth, soil structure and overall health Albrecht formula 65-75% Ca, 10-15% Mg, 2-5% K, 0.5-3% Na and about 10-15% H Reality check: Crops can handle a wide range of nutrient ratios without difficulty Soil physical properties can be related to cation composition, but no set cation ratio fits all soil situations Economics of balancing nutrients not realistic

What can you infer from a soil test about soil nitrogen status? Common soil test N parameters : Organic matter Total N NO 3 -N

Soil organic matter and soil total N are correlated : Soil total N (%) 0.2 0.16 0.12 0.08 0.04 0 conventional organic y = 0.07x r 2 = 0.79 0 1 2 3 Soil organic matter (%) Soils in vegetable rotations

N mineralization potential is correlated with organic matter : N mineralization (lb N/acre/day) 2.5 2.0 1.5 1.0 0.5 0.0 conventional organic r 2 = 0.61 0 1 2 3 Soil organic matter (%) Soils collected between cropping seasons (no recent organic matter additions) aerobic incubation at 77 o F

Typical soil NO 3 -N pattern for an organic annual crop : Soil NO3-N (PPM) 25 20 15 10 5 0 Incorporate cover crop Plant spring crop Mar Apr May Jun Jul Aug Month Crop N uptake exceeds soil N mineralization

In-season soil nitrate monitoring : Soil nitrate quick test Soil test interpretation : > 10 PPM NO 3 -N = adequate for current growth < 5 PPM = very limited N availability

Tissue analysis for organic production?

Tissue analysis for organic production? Are tissue sufficiency standards the same for organic and conventional production?

What are we trying measuring? recent nutrient uptake in petioles unassimilated nutrients (NO 3 -N, PO 4 -P, K) overall plant nutrient status in whole leaves total N, P, K

Tissue testing for P and K : 1) crop sufficiency / deficiency can usually be predicted from a soil test, so tissue testing is of secondary importance 2) P and K soil availability is similar between conventional and organic production, so tissue diagnostic standards should be similar

Tissue testing for N : - do organic crops take up different forms of N? - do organic crops process N differently?

Compare 2008 UCD conventional trial with 2 organic processing tomato fields

Xylem total N (PPM) 200 150 100 50 0 early flower Conventional adequate N Conventional deficient N Organic full bloom crop growth stage

Xylem total N (PPM) Xylem NO 3-N (% of total N) 200 150 100 50 0 100 80 60 40 20 0 early flower Conventional adequate N Conventional deficient N Organic full bloom crop growth stage early flower Conventional adequate N Conventional deficient N Organic full bloom crop growth stage Conclusion: Organic and conventional systems do not differ dramatically in the forms of N taken up, or the way the crop processes N

Is petiole NO 3 -N testing useful? Tomato petiole NO 3 -N concentration at early flower stage, UCD Sustainable Agricultural Farming Systems project : Petiole NO 3 -N (PPM) Organic system Year Organic Conventional N deficient? 1994 4,300 14,300 yes 1995 1,000 7,900 yes 1996 7,900 12,400 no 1997 10,900 8,400 no 1998 15,200 10,000 no Sufficiency threshold: > 5,000 PPM at early bloom?

Is petiole NO 3 -N testing useful? 2000 Yolo organic tomato sidedress trial : No sidedress vs. 120 lb/acre N with high-n organic fertilizer Petiole NO 3 -N (PPM) Yield Treatment early flower full bloom (tons/acre) No sidedress N 3,400 100 20 Seabird guano 6,200 4,400 36 Blood meal 5,500 3,400 34 Fish powder 5,900 4,200 35 Sufficiency threshold 5,000? 2,000?

Is whole leaf total N testing useful? Conventional sufficiency standards should be generally applicable : if organic meet these standards, sufficiency presumed if organic substantially below these standards, deficiency likely

Is whole leaf total N testing useful? 2000 Yolo organic tomato sidedress trial : No sidedress vs. 120 lb/acre N with high-n organic fertilizer Leaf N (%) Yield Treatment First flower Full bloom (tons/acre) No sidedress N 3.9 2.8 20 Seabird guano 4.3 4.2 36 Blood meal 4.1 4.1 34 Fish powder 4.2 4.3 35 Sufficiency minimum 4.0 3.5

Is whole leaf total N testing useful? 1999 LTRAS tomato trial, sampled at fruiting : Management system Leaf % N Fruit yield (tons/acre) Organic 3.0 33 Transitional 3.1 35 Transitional +80 lb N/acre 4.4 39 Sufficiency threshold 3.5 39

In summary : Tissue analysis can have merit for organic production Conventional P and K sufficiency standards should apply to organics, but some modification necessary for N status Developing your own database across years most useful