Napoli Experimental Site

Differently from previous experimental sites, the first year of cultivation produced a deterioration of soil structural properties in the field plots of Napoli (Table 4.5). With respect to the initial control soil, nearly all treatments showed lower yields of large size aggregates, with consequent decrease in soil stability index. The loss of structural stability in maize cultivated plots may be due to specific properties of the sandy-clay loam soil of this site. An exception was the soil treated with the low compost rate (COM-1). This showed a MWD increase, due to an effective association of soil particles into larger aggregate fractions, which included more than 50% of total fraction mass. The addition of the low compost rate (COM-1) may have promoted a microbially induced priming effect with a temporary improvement of macroaggregate formation (Chan and Heenan 1999).

In the case of wheat fields, both CAT and No-CAT treatments revealed an improvement of soil structural properties as compared to maize fields, thus suggesting a crop effect on soil physical parameters (Table 4.5).

Table 4.5 Napoli experimental site, percent distribution (%) of water-stable aggregate sizes (mm), mean-weight diameter index (MWD) (mm), under different treatments for three experimental years

Treatments

Aggregate size

MWD

4.75-1.00

1.00-0.50

0.50-0.25

<0.25

Control soil

39.2

30.8

14.3

15.7

1.43

Maize

First year

TRA

33.3

32.4

16.6

17.6

1.29

MIN

31.9

35.4

18.4

14.2

1.27

GMAN

28.7

39.8

16.8

14.7

1.20

COM-1

53.6

26.9

9.5

10.0

1.79

COM-2

37.3

31.4

12.7

18.6

1.38

LSD

3.3

1.1

3.7

4.7

0.19

Second year

TRA

26.4

40.1

20.1

13.4

1.15

MIN

33.1

41.6

15.8

9.5

1.33

GMAN

32.4

38.4

17.3

11.9

1.30

COM-1

37.6

37.2

14.9

10.4

1.42

COM-2

32.6

36.5

18.1

12.8

1.30

LSD

5.3

3.7

2.1

1.2

0.10

Third year

TRA

38.7

33.7

16.1

11.5

1.44

MIN

40.8

31.9

16.1

11.2

1.49

GMAN

46.1

31.4

13.2

9.3

1.62

COM-1

43.1

29.9

15.5

11.5

1.54

COM-2

43.2

32.6

14.7

9.5

1.55

LSD

2.2

NS

NS

2.4

0.06

Wheat

First year

CAT

51.3 (2.4)

25.9 (1.9)

11.2 (2.3)

11.6 (1.7)

1.73 (0.06)

No-CAT

47.5 (7.3)

28.2 (4.3)

13.3 (2.0)

10.9 (2.7)

1.64 (0.18)

Second year

CAT

31.5(2.7)

40.0(0.4)

17.1(1.7)

11.4(1.5)

1.28(0.1)

No-CAT

36.7(6.0)

40.2(3.0)

13.2(1.9)

9.9(1.1)

1.42(0.1)

Third year

CAT

41.6(1.9)

32.7(0.3)

15.2(0.6)

10.4(0.9)

1.51 (0.05)

No-CAT

39.7(2.2)

35.0(1.4)

15.2(0.5)

10.1(0.4)

1.47 (0.05)

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

A slight different distribution of water-stable aggregates was observed in the maize plots after two experimentation years. For all treatments, soil aggregate fractionation indicated a decrease in microaggregate yield and a corresponding, though uneven, increase in macroaggregates, this trend being more effective for COM-1 (Table 4.5). For maize fields, soil aggregate distribution decreased the

MWD index, with respect to the first year, for all treatments except for MIN and GMAN. The MWD stability index for both CAT and No-CAT treatments was also reduced in the second year to the levels similar to those of maize fields.

Similar to other experimental sites, the Napoli field site presented a structural improvement in soils of all treatments after three experimental years (Table 4.4). Either maize or wheat plots produced an increased amount of large macroaggregates fraction, with a consequent improvement of MWD values, which were larger than for the initial undisturbed control soil.

The best structural quality was found for treatments with organic amendments, including green manure, and for CAT, although for the latter the difference from No-CAT was not statistically significant (Table 4.5).

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