Fertilizer Economics Allocating Funds Across Nutrients

Transcription

1 Fertilizer Economics Allocating Funds Across Nutrients Tom Jensen, PhD. Agronomy, CCA, P.Ag. Northern Great Plains Director International Plant Nutrition Institute (IPNI) Saskatoon, SK

2 Deciding on fertilizer rates in a time of fluctuating fertilizer and crop prices. The most common question expressed at crop production meetings this past summer and fall has been How much can I cut back on fertilizer and not decrease my crop yields?. There is no simple answer, but I will first review some basic principles of fund allocation for plant nutrients, by summarizing an article prepared by Dr. Scott Murrell and Dr. Tom Bruulsema of IPNI in a recent Better Crops With Plant Food article (no. 3, 2008). This was reprinted in the Nov Top Crop Manager magazine. Secondly, I will discuss real life field fertilizer situations that exist in Western Canada and describe how a crop advisor might assist our farm clients.

3 Figure 1. A conceptual model of crop response to soil nutrient supply.(murrell and Bruulsema 2008)

4 Figure 2. A conceptual model of the interaction of two nutrients on crop yield. (adapted from Figure 2-4 on p. 99 in Black, 1993). (Murrell and Bruulsema 2008)

5 (Murrell and Bruulsema 2008)

6 (Murrell and Bruulsema 2008)

7 How much can I cut back on fertilizer and not decrease my crop yields? Often, as a crop advisor, to answer a question effectively you need to ask some questions to find out what the farm client really wants to know. What do you mean when you say you will cut back on fertilizer? Do you think your regular fertilizer rates are excessive? Are you only looking at decreasing your rates because fertilizer prices have increased? Have you considered each field separately and how a broad, general cut back in fertilizer rates on all fields will affect yield on specific fields? Will you increase your fertilizer rates again when fertilizer prices decrease relative to crop prices?

8 What do you mean when you say you will cut back on fertilizer? Often the response is as follows: I won t reduce my N rates much as this will adversely affect my yields right away. I ll just fine tune my rates of N. More decisions based on soil testing results Apply fertilizer N based on crop need and removal in grain Be careful not to apply more than required

9 What do you mean when you say you will cut back on fertilizer? (continued) Response continued For P, K, S and micronutrients, I will apply twothirds to one half as much P, and skip K, S, and micros. When might this approach be valid? On a field where there has been a consistent program of building up the background availability of P, K, S and other secondary and micronutrients as needed. Soil test results show adequate to excess availability When might this approach be invalid? On a field where there has been no building up, or even replacement of P, K, S and micronutrients. Soil-test results show marginal to deficient levels of P, K, S and micronutrient availability.

10 Specific Challenges with Reduced Phosphorous Rate Strategies 1. Designer P based liquid starter applied at about one third the normal rate of P. E.g seed row solution at 3 US gal/acre (8 lb P2O5/acre) that costs less than a 46 lb /acre granular seed row application (24 lb P2O5/acre rate). Yes the application is convenient, it costs less per acre, there is less volume of fertilizer to apply, but You pay more per unit of P2O5, and even though your crop yields may not decrease in the short term (i.e. 2 to 3 years), your mining the more easily available P out of your soil, and in the longer term lower crop yields will result.

11 Specific Challenges with Reduced Phosphorous Rate Strategies (continued) 2 2. I will apply P at rates one half of my normal rate. It costs less per acre, but Your crop yields may not decrease in the short term (i.e. 2 to 3 years), your mining the more easily available P out of your soil, and in the longer term lower crop yields will result.

12 Specific Challenges with Reduced Phosphorous Rate Strategies (continued - 3) 3. I can get a good deal on Rock Phosphate and I will apply P at my regular rate (e.g. 24 lb P2O5/acre). For example $500/tonne for rock phosphate compared to $1150/tonne for , both farm delivered prices. Product Rock Phosphate P2O5 Content Soluble P2O5 Content Cost $/tonne Cost $/lb P2O5 Total Cost $/lb P2O5 soluble 26.6% 5.8% $500 $0.85 $ % 47.3% $1150 $1.00 $1.10 Rock phosphate does contain P, but it is in a form that is less soluble and available to crops than the soluble forms of processed material as granular , or liquid (these are acidulated [ground and treated with sulfuric acid]) and filtered from rock phosphate Rock phosphate applications can work quite well on very acidic soils (<ph 5.0), but on high ph soils (>7.0) the natural acidulation process doesn t happen.

13 Efficiency of P Fertilizers In the year of application uptake of P from P fertilizer is usually 25% or less using the direct labeled method. Calculated as the amount of labeled P ( 32 P labelled fertilizer) taken up in the crop as a percentage of labeled P fertilizer applied. However when measured a number of years and crops in a rotation using the balance method, the efficiency is often up to 90%. Calculated as the total P in the crop divided by P applied, expressed as a percentage

14 Ideal P Management 1. Build up P availability to a critical soil test level This critical soil test level is soil specific, but near the sufficiency range, but not excess 2. Continue to apply P at rates close to crop removal This approach is based on research described by A.E. (Johnny) Johnston a researcher at Rothamsted Research Station in England. It can result in as efficient uptake of P as can be achieved and results in as high of yields of crop possible as long as other nutrients and agronomic practices are optimized.

15 Critical P Availability Level Approach (Syers et al 2008)

16 Conclusions 1. The lower the amount of soil available nutrient in a field, there is less opportunity to cut back and save money 2. When allocating funds between two or more different plant nutrients, take into consideration the cost and potential response to each nutrient. 3. Encourage farm customers to determine the availability of plant nutrients on each individual field. 4. The apparent low P fertilizer use efficiency in a year of application is much higher over the long term due to plant use of soil residual P. 5. Consider managing P using the critical response level approach.

17 Questions