Analyses of various composts

Source

N%

P%

K%

N+P+K%

Ca%

ON Rat

Vegetable trimmings and paper

1.57

0.40

0.40

2.37

7

24:1

Municipal refuse 1

0.97

0.16

0.21

1.34

?

24:1

Municipal refuse 2

0.91

0.22

0.91

2.04

1.91

36:1

Municipal refuse 3

1.1

0.6

0.9

2.6

?

?

Missouri tree service (wood waste)

0.4

0.06

0.2

0.6

1.13

88:1

Missouri farm

1.8

1.5

1.4

4.7

2.35

24:1

Missouri home garden

2.1

0.1

0.5

2.7

0.16

21:1

Gainesville, FL, refuse

0.57

0.26

0.22 I

1.05

1.88

?

Garden compost A

1.40

0.30

0.40

2.1

7

25:1

Garden compost B

3.50

1.00

2.00

I 6.50

r

10:1

CA commercial for veg A

1.6

?

?

4.2

?

15:1

CA commercial for veg B

2.0

?

7

6.8

7

13:1

Poultry manure compost

3.9

?

?

7.6

7

7:1

Poultry manure compost Poultry manure compost

3.6 4.0

2.6

1.7 3.9

7.8 I 10.5

6.94 7.14

7:1 7:1

Note: These figures have been gathered from various sources over many years; not all sources provided data for all columns.

The column "N+P+K%" is a useful gauge of overall mineralization. Figure 7.2

do a grear job ac growing food. The he was cold so many times ^ thosc it came to beheve it themselves. But if compose is going co noticeably improve che growth of most kinds of vegetable crops, it has to have a nitrogen content in excess of 1.5 percent and a C/N no higher chan 15:1, and ic muse contain significant amounts of phosphorus, potassium, calcium, magnesium, and trace minerals, all in the right proportions. Not all composts do; most, in fact, done as shown in Figure 7.2.

Please noeice in che cable that municipal refose compost isn't potent enough for vegetable growing. That's because much of the material going into che heap is paper and cardboard, chipped cree crimmings, and ocher woody waste. All these materials have a high C/N, and the average C/N of the heap when composting starts exceeds 50:1. After much heacing and watering and turning and shrinking and rewatering and turning some more, the C/N drops to about 25:1. In other words, far more than half the carbon has disappeared. Why "far more" and not exactly half the carbon as those numbers might suggest? Because the way municipal compost is made causes most of the nitrogen to disappear as well. The final weight of compost will be only a tiny fraction of the starting weight. Thus municipal composting, portrayed as socially positive, actually is a huge contributor to greenhouse gasses.

Municipal composting operations find it impossible co get market gardeners to accept their product. Ultimately its destiny is to be mulch along roadsides, under ornamentals in parks, and sometimes in homeowners' yards and gardens. Those who foolishly try to use it to grow vegetables are sorely disappointed.

What I would classify as low-grade compost, barely suitable for a garden, contains around 1.5 percent nitrogen, its carbon-nitrogen ratio is around 20:1. and its total of N + P+K. is under 3 percent. In climates where the soil gees warm if you shallowiy rake in a small amount (maybe a layer a quarter to a half inch thick — 6 co 12 millimeters), ehis low-grade scuff will barely teed the sort of vegetables 1 call "low demand" (see the sidebar in Chapter 2).

To modestly grow healthy medium-demand vegetables in most climates and soils, what I would classify as medium-quality compost needs to be added to the soil at about the same rate noted in the previous paragraph. Medium-quality compost contains more like 2 percent nitrogen, has a N+P + K ot around 4+ percent, and has a C/N no higher than 15:1.

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