How long does it take to improve soil ? - Polyculture Market Garden Study

One of the things I love most about the way we grow is how each year everything seems to improve - richer biodiversity, more and tastier produce and healthier soils.

We've been monitoring what effect our cultivation practices have on the soil to see whether our observations are confirmed by testing. We take two soil samples from our gardens, one in March before fertilising and another in November after the last crops are harvested.

We started the market garden in March 2015. The results below represent the first and second soil tests in the garden and results from samples taken in March of this year.

Soil Mineral Analysis and pH

Click here to see tables: http://balkanecologyproject.blogspot.bg/2016/04/13-months-soil-shows-clear-signs-of.html

2015
March pH (KCI) N03N NH4N P205 K20
5.69 15.4 2.89 16.3 13
November pH (KCI) N03N NH4N P205 K20
6.44 16.2 4.45 43.9 14.4
2016
Nitrogen mg/kg Potassium and Phosphorous mg/100g
March pH (KCI) N03N NH4N P205 K20
6.65 4.43 5.79 88 25.2

It's pleasing to see our market garden soils improving after the first year of cultivation and that's with taking out 358 kg of produce last year (see here for a summary of all results).

Also interesting to see is the reduction in plant available N (N03N) from Nov- March, probably due to high levels of carbon rich straw mulch left over after the growing season. The soil microbiota will be using the nitrogen to break down the high carbon straw.

Soil Health Visual Testing

As well as the laboratory analysis of our soils we also take visual tests using a soil health test developed by farmers for farmers to track the development of soil health. These test show great improvements in the soil over a period of just 13 months.

Polyculture Study team carrying out soil heath test in the market garden.
Soil Test Card comparison 2015 vs 2016
2016 TEST RESULT TEST SCORES 1 - 9
POOR 1 --------- 2 --------- 3 FAIR 4 --------- 5 -------- 6 GOOD 7 ---------- 8 --------- 9 1 2 3 4 5 Av
1.GROUND COVER Less than 50% ground cover [ground plants or mulch 50% to 75% ground cover [ground plant or mulch] more than 75% ground cover [ground plant or mulch] 9 9 9 9 9 9
2.PENETROMETER Wire probe will not penetrate Wire probe penetrates with difficulty to less than 20 cm Wire probe easily penetrates to 20 cm 9 4,5 9 5,5 5,5 6.7
3.INFILTRATION More than 7 minutes 3 to 7 minutes Less than 3 minutes 9 9 9 9 9 9

1. DIVERSITY OF MACROLIFE Fewer than two types of soil animals Two to five types of soil animals More than five types of soil animals 9 9 7 9 9 8.6
2. ROOT DEVELOPMENT Few fine roots only found near the surface Some fine roots mostly near the surface Many fine roots throughout 9 7 7 8 8 7.9
3. SOIL STRUCTURE Mostly in clods or with a surface crust, few crumbs Some clods but also many 10mm crumbs Friable, readily breaks into 10mm crumbs 6 5 6 4 6 5.4
4. AGGREGATE STABILITY Aggregate broke apart in less than one minute Aggregate remained intact after one minute Aggregate remained intact after swirling
   10cm depth 8 9 8 8 8 8.2
   20 cm depth not taken not taken not taken not taken not taken not taken
5. EARTHWORMS 2 4 1 9 5 4.1
   Total 58.9
   2015 TEST RESULT TEST SCORES 1 - 9
   POOR 1 --------- 2 --------- 3 FAIR 4 --------- 5 -------- 6 GOOD 7 ---------- 8 --------- 9 1 2 3 4 5 Av
   1.GROUND COVER Less than 50% ground cover [ground plants or mulch 50% to 75% ground cover [ground plant or mulch] more than 75% ground cover [ground plant or mulch] 8 6 7 7 7 7
   2.PENETROMETER Wire probe will not penetrate Wire probe penetrates with difficulty to less than 20 cm Wire probe easily penetrates to 20 cm 6 4 4 3 3 4
   3.INFILTRATION More than 7 minutes 3 to 7 minutes Less than 3 minutes 4 1 1 1 1 1.6
6. DIVERSITY OF MACROLIFE Fewer than two types of soil animals Two to five types of soil animals More than five types of soil animals 1 1 1 1 1 1
7. ROOT DEVELOPMENT Few fine roots only found near the surface Some fine roots mostly near the surface Many fine roots throughout 4 6 6 5 5 5.2
8. SOIL STRUCTURE Mostly in clods or with a surface crust, few crumbs Some clods but also many 10mm crumbs Friable, readily breaks into 10mm crumbs 5 4 6 4 5 4.8
9. AGGREGATE STABILITY Aggregate broke apart in less than one minute Aggregate remained intact after one minute Aggregate remained intact after swirling
   10cm depth 4 5 3 7 8 5.4
   20 cm depth 7 7 8 8 6 7.2
10. EARTHWORMS 0 5 5 3 3 3.2
    Total 39.4