1 Quantitative concepts and skills Proportions Dry weight calculations Density Unit conversions Subtraction Organic Nitrogen Fertilizers Module X Organic fertilizers vary widely in their nutrient contents. How does the carbon-to- nitrogen ratio of the fertilizer influences the release of nitrogen to plants? After adding a dump truck of compost to an acre field, how much nitrogen will become available for plants ? Steve Scheuerell, TESC

2 PREVIEW When organic matter is added to soil, soil microbes begin to decompose it, and microbes take up carbon and nitrogen to grow. The carbon to nitrogen ratio of the organic matter determines if there is sufficient nitrogen in the organic matter to meet microbial demand and still have nitrogen left over for plants. On average, one atom of nitrogen is immobilized by soil organisms for every 15 atoms of carbon consumed. If there is too much carbon relative to nitrogen, soil microbes will immobilize nitrogen from the soil and plants will not have nitrogen to use for growth. For simplicity sake, in this module it is assumed that the soil biota would consume all of the carbon in the added organic matter.

3 PREVIEW cont. Slide 4 introduces the properties of organic materials that are needed to calculate dry weight bulk density. Slides 5-6 have you compute the carbon to nitrogen ratio and weight of carbon and nitrogen per cubic yard of organic material. Slide 7 introduces the concept of soil microbial demand for nitrogen based upon the amount of carbon. Slide 8 calculates the amount of nitrogen released from a cubic yard of dairy compost. Slide 9 takes into account the total amount of organic matter applied with a 20 cubic yard dump truck and the total amount of nitrogen released from the organic matter that would be available for plants. Slide 10 introduces unit conversions by calculating the metric dry bulk density of the organic matter. Slides 11 repeat the calculations of slides 6-9 to calculate values in metric units. Slides 12 asks you to consider different types of organic matter and how they vary from the example of composted dairy manure. In Slide 13 you will enter further data, use the spreadsheet to do calculations for you, and relate it to a graph. The spreadsheet can be used to convert this data to metric units in slide 14. Slide provides questions to reflect upon, and asks you to do further calculations while manipulating the spreadsheets you have created. 3

4 Starting calculations that we’ll build upon. Recreate this spreadsheet in Excel. What is the equation in the circled box? Before determining how much carbon and nitrogen are in any type of organic matter, you need to account for the proportion of weight due to water. Bulk density is a measurement of weight per unit volume. It is a commonly measured characteristic of bulk organic materials. = Cell with an equation in it. = Cell with a number in it.

5 Determine the equation used to calculate the carbon-to-nitrogen ratio (C/N) Add rows to your spreadsheet and fill in the labels and data. Do this for all subsequent slides as the spreadsheet get larger.

6 Determine the equations used to calculate the weight of carbon and nitrogen in a cubic yard of dairy manure compost

7 In this slide we determine the amount of N immobilized by soil microbes due to the consumption of carbon in the organic matter added to soil Use the information in slide 2 to determine the equation in the circled cell

8 Determine the equation used to calculate the amount of N available to plants per cubic yard of dairy compost Assume that soil microbes get all of their N before plant roots get any N. Also assume that all N left after satisfying soil microbes is available to plants.

9 What is the equation used to determine the total N released per acre from the dump truck load of dairy manure compost? Time to account for the entire dump truck load!

10 To convert from English to metric bulk density multiply the English value by Most people in the world perform measurements and calculations using the metric system. Here we’ll convert our data to metric units

11 Determine the equations used in column C, rows Note that row 16 converts cubic yards to cubic meters. Also assume the same volume was applied to one ha. Think about how you can copy and modify the existing equations in you spreadsheet

12 Consider different types of organic matter that could be added to soil Using the following slide, copy the column labels and lightly shaded numerical data into your spreadsheet. Do you have to copy in the darker shaded data or can the spreadsheet do the calculations for you? Identify which rows of data are used to create the graph below the spreadsheet. Pick two points on the graph. Find the corresponding data in the spreadsheet. Repeat this exercise for slide 14.

13 Different types of organic matter that could be added to soil

14 Conversion to metric units – use the spreadsheet to make the calculations Note how conversion to metric unit of mass changes the y-axis scaling in the graph to the right

15 Looking back and going forward Which organic materials released N to plants? Which materials caused an overall reduction of soil N availability? What is the relationship between the C/N ratio of organic matter and N release or immobilization in the soil? At the rates applied, would any of the organic materials be of concern in relation to N pollution? Table 12.2 on page 506 of Brady and Weil has C and N contents for many organic materials that you may use one day. Add several to your spreadsheet, assume a moisture content and bulk density, and calculate the amount of N released or immobilized. Graphing –Use Excel to create a scatter plot graph similar to the one on slide 14.

16 Manipulating the spreadsheet to explore real-world scenarios Calculations 1.If you wanted 50, 100, or 150 kg/ha N available for plant growth, how many m 3 of blood meal, laying hen manure, and dairy compost should be tilled in per hectare? Design a simple spreadsheet to solve these calculations. 2.Changing the ratio of C and N immobilized by soil biota will affect how much N is released to plants. We have used a C:N ratio of 15:1. Now see what effect a ratio of 10:1 or 20:1 would have on N availability. To see this effect using the spreadsheet, go to slide 14 and vary the N uptake function in row 13. Change the equation denominator to 10 for all materials and observe the effect on N availability. Repeat this using 20 in the denominator. For each change, describe which materials either release or immobilize N in the soil. 3.Bringing in soil ecology knowledge from our class. How would the presence or absence of secondary consumers in the soil food web affect the release of N from organic materials added to the soil? See chapter 12 in Brady and Weil if you are stuck. 4.On slide 11, row 16 of the spreadsheet, cubic yards were converted to cubic meters but it was assumed that the same volume was applied to one ha instead of one acre. If you wanted to apply the same volume compost per square area, how many cubic meters would be needed to cover one ha? Make this change and compare the N released/immobilized on slide 14.