Torino Experimental Site

After the first year, the majority of treatments on maize plots of Torino showed a significant increase of aggregate stability with respect to the initial soil (Table 4.3). Only the addition of green manure (GMAN) and the lower rate of compost (COM-1)

Table 4.3 Torino experimental site, percent distribution (%) of water-stable aggregate sizes (mm) and mean-weight diameter index (MWD) (mm) under different treatments for 3 years of experimentation

Treatments

Aggregate size

MWD

4.75-1.00

1.00-0.50

0.50-0.25

<0.25

Control soil

9.7

21.1

27.5

41.8

0.59

Maize

First year

TRA

15.7

27.1

26.9

30.4

0.79

MIN

13.2

30.9

27.6

28.3

0.75

GMAN

10.8

26.5

31.1

31.6

0.67

COM-1

9.0

27.9

32.0

31.1

0.65

COM-2

14.7

29.3

27.2

28.9

0.78

LSD

1.7

NS

3.2

1.2

0.04

Second year

TRA

8.8

25.5

39.8

25.9

0.63

MIN

9.6

23.4

38.7

28.2

0.63

GMAN

10.3

24.1

39.7

25.9

0.66

COM-1

9.6

24.1

38.5

27.8

0.64

COM-2

9.7

26.6

39.9

23.8

0.66

LSD

NS

NS

NS

NS

NS

Third year

TRA

11.4

25.0

36.2

27.5

0.68

MIN

9.8

21.2

38.0

30.9

0.62

GMAN

9.4

19.4

38.3

33.0

0.60

COM-1

15.3

25.2

34.5

25.1

0.79

COM-2

20.3

27.7

29.8

22.2

0.93

LSD

2.5

2.2

2.1

2.2

0.06

Wheat

First year

CAT

19.4 (4.2)a

25.0 (4.4)

25.8 (3.8)b

29.8 (8.3)

0.88 (0.11)

No-CAT

12.9 (2.2)b

28.5 (2.5)

32.3 (1.1)a

26.2 (0.9)

0.74 (0.05)

Second year

CAT

9.5 (1.2)b

23.4 (1.2)

38.2 (3.8)a

28.9 (8.7)

0.64 (0.03)

No-CAT

11.3 (1.7)a

22.5 (1.3)

33.0 (1.7)b

33.1 (2.8)

0.66 (0.04)

Third year

CAT

10.3 (1.5)

25.0 (1.9)

36.5 (1.4)

28.2 (2.7)

0.66 (0.05)

No-CAT

10.6 (1.4)

24.3 (5.2)

33.9 (3.3)

31.1 (5.4)

0.65 (0.05)

LSD least significant difference (n = 4), NS not significant. Different small letters in columns indicate significant difference at 0.05 probability level (n = 4). Numbers in brackets for wheat plots represent standard deviation (n = 4)

LSD least significant difference (n = 4), NS not significant. Different small letters in columns indicate significant difference at 0.05 probability level (n = 4). Numbers in brackets for wheat plots represent standard deviation (n = 4)

produced smaller MWD increases. All field treatments revealed a positive effect in the distribution of water-stable aggregates, with an overall decrease in the yield of microaggregates (<0.25 mm), which were steadily incorporated in upper size-classes. The widespread increase of soil aggregation may be explained with the physical action of plant roots and fungal hyphae, as well as root debris and microbial bio-products, which promote association of small soil fractions into meso- and macroaggregates (Tisdall and Oades 1982; Chan and Heenan 1999; Six et al. 2004). For the GMAN and COM-1 treatments, the effect was limited to the intermediate particles size fraction (1-0.25 mm), while for traditional (TRA), minimum tillage (MIN), and greater compost rate (COM-2), there was a significant particle incorporation also in the large macroaggregate class, with a consequent increase of MWD.

As compared to both initial (control) and untreated plots (No-CAT), an increase of MWD index (Table 4.3) was observed for the soil added with biomimetic catalyst (CAT), indicating that this treatment induced a redistribution of macroaggregates into larger sized fractions. However, this effect may have also been partially favored by the action of plant roots and microbial biomass.

After the second year, an overall stabilization of structural properties was noted with an even distribution of water-stable aggregates and a similarity of MWD index for all soil treatments. With respect to previous year, a MWD decrease was found for TRA, MIN, and COM-2, whose values approached those for GMAN and COM-1, which instead maintained a steady effect on soil aggregates. The aggregate distribution for the second year (Table 4.3) showed a further decrease of microaggregate sizes for all treatments,with their prevalent incorporation into the next larger size-fraction (0.50-0.25 mm). Concomitantly, the trend of decreasing aggregate stability for TRA, MIN, and COM-2 was mainly due to decrease of large macroaggregates, whose values remained unvaried only for GMAN and COM-1 treatments.

In the second year, soils treated with the biomimetic catalyst (CAT) showed a breakdown of larger aggregates, with soil redistribution in smaller macroaggregates and MWD index returning to No-CAT values.

Soil samples under traditional soil management did not show a significant variation in structural stability after 3 years of experimentation, except for only a slight increase in microaggregate yield (Table 4.3). Conversely, both COM-1 and COM-2 revealed a positive effect on structural properties. In fact, their stability index increased, due to decrease of both microaggregates and small macroaggregates (0.50-0.25 mm), which apparently aggregated into larger sized fractions. This improvement in soil stability was consistent with the amount of added compost, since the larger compost addition (COM-2) provided a greater response. In fact, the yield of large macroaggregates for COM-2 was twice as large as that for TRA, MIN, and GMAN. No difference in the distribution of water-stable aggregates and MWD index was found between the CAT treatment and its control for the third year.

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