Nutrient Use by the Grass and Nutrient Supply by the Soil

Grass grows in soil, and nutrients used by the grass come either from the soil or from fertilizer. When the soil contains enough of an element to meet all of the grass requirements, none of that element is required as fertilizer. When the grass can use more of an element than can be supplied by the soil, that element must be applied as fertilizer. This seminar will explain how to estimate the maximum amount of an element the grass can use, how to identify the quantity that can be supplied by the soil, and how to use those two amounts to get an estimate of the amount that may be required as fertilizer.

Transcript

1. Nutrient Use by the Grass and Nutrient Supply by the Soil Micah Woods Chief Scientist Asian Turfgrass Center www.asianturfgrass.com 13 January 2016 Northern Green Expo Minneapolis, Minnesota
2. Two questions 1. Is this element required as fertilizer? 2. If it is required, how much should I apply? To answer those questions, we need to know how much is used by the grass and how much can be supplied by the soil.
3. T o a n s w e r t h o s e f u n d a me n t a l q u e s t i o n s , w e n e e d t o e s t i ma t e 3 q u a n t i t i e s c r e e p i n g b e n t g r a s s S h a n g h a i , C h i n a
4. T o a n s w e r t h o s e f u n d a me n t a l q u e s t i o n s , w e n e e d t o e s t i ma t e 3 q u a n t i t i e s c r e e p i n g b e n t g r a s s S h a n g h a i , C h i n a
5. T o a n s w e r t h o s e f u n d a me n t a l q u e s t i o n s , w e n e e d t o e s t i ma t e 3 q u a n t i t i e s c r e e p i n g b e n t g r a s s S h a n g h a i , C h i n a
6. T o a n s w e r t h o s e f u n d a me n t a l q u e s t i o n s , w e n e e d t o e s t i ma t e 3 q u a n t i t i e s c r e e p i n g b e n t g r a s s S h a n g h a i , C h i n a
7. T o a n s w e r t h o s e f u n d a me n t a l q u e s t i o n s , w e n e e d t o e s t i ma t e 3 q u a n t i t i e s c r e e p i n g b e n t g r a s s S h a n g h a i , C h i n a
8. a, b, and c a is a site-specific estimate of plant use. b is the amount we want to ensure remains in the soil a er the plant use is accounted for. This is a minimum we don’t want to drop below. You can think of it as a reserve amount in the soil. This is the MLSN guideline level. c is the amount actually present in the soil. This is the soil test result.
9. MLSN is a value for b amount needed a + b − amount present c = fertilizer requirement Q a is a site-specific use estimate, b is the MLSN guideline, and c is the soil test result.
10. How much can the soil supply? amount present c − MLSN guideline b = amount the soil can supply d
11. a, www.paceturf.org/journal/climate
12. Chiba, Japan
13. Chiba, Japan
14. Chiba, Japan
15. Chiba, Japan
16. 0 10 20 30 40 N K P Ca Mg S Element Amount in bentgrass (g/kg)
17. Represent elements in proportion to N For every 1 pound of N, bentgrass will use 0.5 lb K 0.125 lb P 0.125 lb Ca 0.05 lb Mg 0.05 lb S
18. Amount of elements to apply If you don’t do soil testing, apply each element in proportion to N. This ensures that the grass is supplied with all of each element that it will use. But it is much more e icient to do soil testing.
19. b
20. Using MLSN 1. Keep the soil levels of K, P, Ca, Mg, and S from dropping below the MLSN guideline.
21. Using MLSN 1. Keep the soil levels of K, P, Ca, Mg, and S from dropping below the MLSN guideline. 2. Estimate future use of those elements (a), and make sure that amount can be supplied by the soil, while still keeping the soil above the MLSN guideline (b).
22. Using MLSN 1. Keep the soil levels of K, P, Ca, Mg, and S from dropping below the MLSN guideline. 2. Estimate future use of those elements (a), and make sure that amount can be supplied by the soil, while still keeping the soil above the MLSN guideline (b). 3. If the soil (c) doesn’t have enough to do that, then apply enough of that element as fertilizer (Q) to keep the soil above the MLSN guideline.
23. As an example for K a + b − c = Q
24. As an example for K a + b − c = Q In ppm, a = 67, b = 37, c = 50.
25. As an example for K a + b − c = Q In ppm, a = 67, b = 37, c = 50. amount needed 67 + 37 − amount present 50 = fertilizer requirement 54
26. As an example for K a + b − c = Q In ppm, a = 67, b = 37, c = 50. amount needed 67 + 37 − amount present 50 = fertilizer requirement 54 Convert between 3-dimensional (ppm) and 2-dimensional (ex. g m-2, or lb 1000 -2) based on rootzone depth and soil bulk density. For a 10 cm deep rootzone with bulk density of 1.5 g cm-3, 1 g m-2 equals 6.7 ppm, and 1 lb 1000 -2 equals 33.5 ppm. Using that conversion, Q of 54 ppm is a K requirement of 8 g m-2 or 1.6 lb 1000 -2.
27. As an example for K a + b − c = Q
28. As an example for K a + b − c = Q In lbs/1000 2, a = 2, b = 1.1, c = 1.5.
29. As an example for K a + b − c = Q In lbs/1000 2, a = 2, b = 1.1, c = 1.5. amount needed 2 + 1.1 − amount present 1.5 = fertilizer requirement 1.6
30. As an example for K a + b − c = Q In lbs/1000 2, a = 2, b = 1.1, c = 1.5. amount needed 2 + 1.1 − amount present 1.5 = fertilizer requirement 1.6 Convert between 3-dimensional (ppm) and 2-dimensional (ex. g m-2, or lb 1000 -2) based on rootzone depth and soil bulk density. For a 10 cm deep rootzone with bulk density of 1.5 g cm-3, 1 g m-2 equals 6.7 ppm, and 1 lb 1000 -2 equals 33.5 ppm. Using that conversion, Q of 54 ppm is a K requirement of 8 g m-2 or 1.6 lb 1000 -2.
31. “Precision fertilisation” from STERF