Agrovoc descriptors: soil; soil fertility; soil types; farmyard manure; straw; inorganic fertilizers; organic fertilizers; nitrogen fertilizers; fertilizer application; experimentation; rotational cropping
Agris category code: P34; F04
Soil organic matter changes according to the application of organic and mineral fertilizers within long-term experiments
Monika CVETKOV1, Anton TAJNŠEK2
Received July 6, 2009; Accepted August 24, 2009. Prispelo 6. julija, 2009; sprejeto 24. avgusta 2009.
ABSTRACT
Within the long-term field experiments at IOSDV Jable near Ljubljana (subalpine climate, heavy hydromorphic silt loam) and at IOSDV Rakičan (Pannonian climate, sandy silt), the impact of organic matter management system and mineral nitrogen fertilization on the soil organic matter content was studied in the period 1998-2008. The following management systems were selected: system A - no organic matter, system B - farmyard manure ploughing in, system C - straw/catch crop ploughing in. Four different mineral N rates (N0, N1, N2, N3) were evaluated. During the three-year crop rotation, maize, wheat and barley (or, alternatively, oats) were sown each year. The annual balance of Corg was calculated on the basis of the quantity of added organic and mineral fertilizers, considering the quantity of Corg in the soil. In system A, at both locations, fertilizing with the highest amount of mineral N resulted in a higher Corg content. At both locations, positive effect of organic fertilization on the increase of the Corg content was registered where management systems with organic matter (i.e. systems B and C) applied, while statistically significant impact of mineral N on a higher Corg content was determined only in system C. Within all three systems, the highest Corg values were reached when the highest mineral N application volume was used. After 11 years, the Corg content in system A decreased irrespective of the mineral N fertilization at both locations. At IOSDV Jable, a small decrease of the Corg content was measured in BN0, while all other treatments at IOSDV Jable and at IOSDV Rakičan resulted in an increased Corg content.
The average absolute value of difference among the Corg contents in 2008 and 1998 in all ten treatments at IOSDV Jable was 1.8 t/ha Colg, while at IOSDV Rakičan it amounted to 3.5 t/ha Corg, which indicates a major influence of management system on the soil with a smaller clay content.
Key words: soil fertility, crop rotation, organic fertilizers, farmyard manure, straw, N fertilizers, humus content, humus balance
IZVLEČEK
SPREMEMBE VSEBNOSTI ORGANSKE SNOVI V TLEH V ODVISNOSTI OD GNOJENJA Z ORGANSKIMI IN MINERALNIMI GNOJILI ZNOTRAJ TRAJNIH POSKUSOV
V statičnem poskusu IOSDV Jable, blizu Ljubljane (predalpsko klimatsko območje, ilovnato meljasta hidromorfna tla) in IOSDV Rakičan (panonsko klimatsko območje, meljasto ilovnata tla) smo preučevali vpliv gospodarjenja z organskimi gnojili in vpliv gnojenja z mineralnimi dušikom na vsebnost organske snovi v tleh v letih 1998 do 2008. Vključeni sistemi gospodarjenja so bili: sistem A - gospodarjenje brez organskega gnojenja, sistem B -gnojenje s hlevskim gnojem, sistem C - zaoravanje slame/podorin. Preučevane so bile štiri stopnje gnojenja z mineralnim dušikom: N0, N1, N2 in N3. V triletnem kolobarju si sledijo koruza, pšenica, ječmen/oves. Letna bilanca Corg je bila izračunana na podlagi količin dodanih organskih in mineralnih gnojil, pri upoštevanju stanja Colg v tleh. Na obeh lokacijah je v sistemu A gnojenje z največjim odmerkom mineralnega dušika povečalo vsebnost Colg v tleh. Na obeh lokacijah je bil dokazan vpliv organskega gnojenja na povečanje vsebnosti Colg, v sistemih B in C, medtem ko je bil značilen vpliv gnojenja z mineralnim dušikom dokazan le v sistemu C. Najvišje vsebnosti Corg znotraj sistemov so bile pri obravnavanju z največjim odmerkom mineralnega dušika. Po enajstih letih se je vsebnost Colg v sistemu A na obeh lokacijah zmanjšala, ne glede na gnojenje z mineralnim dušikom. Vsebnost Corg je po enajstih letih narasla v vseh obravnavanjih sistemov B in C, razen pri obravnavanju BN0 v IOSDV Jable. Povprečna absolutna razlika vsebnosti Corg med letoma 2008 in 1998 znotraj vseh deset obravnavanj v IOSDV Jable je 1,8 t/ha Corg, v IOSDV Rakičan pa 3,5 t/ha Corg. Rezultati nakazujejo, da je vpliv različnega sistema gospodarjenja večji na lokaciji IOSDV Rakičan, kjer vsebujejo tla manjši odstotek gline.
Ključne besede: rodovitnost tal, kolobar, organska gnojila, hlevski gnoj, slama, mineralni dušik, vsebnost humusa, bilanca humusa
1	University of Ljubljana, Biotechnical Faculty, Jamnikarjeva 101, SI-1111 Ljubljana, e-mail: monika.kunaver@bf.uni-lj.si
2	University of Ljubljana, Biotechnical Faculty, Jamnikarjeva 101, SI-1111 Ljubljana, e-mail: tone.tajnsek@bf.uni-lj.si
Acta agriculturae Slovenica, 93 - 3, september 2009 str. 311 - 320
1 INTRODUCTION
Soil organic matter (SOM) is one of the most important determinants of soil quality and is most commonly estimated by determining the soil organic carbon (SOC) content (Rasmussen et al., 1998). A usable way to calculate SOM is by multiplying the percentage of organic carbon by a factor; however, conversion factor varies between 1.6 and 3.3 and this large range is due to the inherent differences between soils and humus composition. Most commonly, a conversion factor 1.72 is used (Körschens et al., 1997; Körschens, 2001; Rasmussen et al., 1998). Definition of soil organic carbon requires a differentiation into two fractions: decomposable organic carbon (Cdecom), which is mainly influenced by cultivation conditions and inert part of carbon (Ciner), which is uninvolved in mineralization and mostly dependent on the site conditions (Körschens,
1997).
It is widely recognized that SOC plays an important role in biological (provision of substrate and nutrients for microbes), chemical (buffering changes, soil porosity) and physical (stabilization of soil structure, soil thermal conditions) properties of the soil (Reeves, 1997). Considering this wide variety of performance indicators, Karlen (Karlen et al., 2003) pointed out that soil quality needs to be assessed with regard to what the soil is used for, as a particular type of soil may be of high quality for one function and may perform poorly for another. Critical levels of soil organic carbon content are difficult to establish since they vary according to soil texture and climatic conditions (Kay and Angers, 1999; Körschens , 1997; Ogle et al., 2005, Rasmussen et al.,
1998).
It is recommendable to maintain a 1.5 to 3.5 % SOC content in topsoil, with the value varying in accordance with the soil structure (Tajnšek, 2003). According to Körschens (Körschens et al., 1997), the upper and the lower values of SOC differ in relation to clay contents; for soils with 4 % of clay, the proposed limits of SOC are between 1 % and 1.5 %, while for soils with more than 38 % of clay, the limit values of SOC are between 3.5 % and 4.4 %. Due to a slow response of organic carbon to the production management, monitoring of humus content requires long-term, several-decade lasting experiments (Körschens, 2001; Powlson et al., 1998; Ogle et al., 1998). Crop rotation, fertilization with organic and mineral fertilizers, a manner and time of ploughing and ploughing in of harvest residues or catch crops are factors that influence the content of SOC. Having replaced the conventional soil tillage with shallow or minimum tillage, soil humus content in the
soil layer to 10 cm significantly increased (Angers and Carter, 1996; Campbell et al., 1996; Riley et al., 2008; Slepetiene and Slepetys, 2005). However, Schulz (Schulz et al., 2008) points out that significant differentiation of SOC content by tillage intensity could not be confirmed.
Bucur et al. (2007) studied the influence of soil erosion on humus losses in different crop systems in Romania; the highest losses were registered in continuous maize culture. Körschens (1997) thoroughly studied the influence of different crops on the decomposable SOC; clover (lucerne, alfaalfa) as a perennial crop with a wide root system proved to have the highest SOC content in comparison with cereals and row crops. With the application of organic manure, the SOM content increased (Delschen, 1999; Edmeades, 2003; Gerzabek ,1997; Körschens, 1997; Kristaponyte, 2005; Martens and Frankenberger, 1992; Nardi et al., 2004; Paustian et al., 2005). The application of higher amounts of mineral fertilizers (NPK or N) increase SOC amount (Haynes and Naidu, 1998; Purakayastha et al., 2008), while, according to Shevtsova and Nardi (Shevtsova et al., 2003; Nardi et al., 2004), fertilizing with mineral fertilizers had no significant effect on the humus content compared to the application of organic fertilizers.
As the humification (changing the primary organic matter into humus) and mineralization (changing humus into soil minerals) depend largely on the amount of precipitation, it is necessary that the latter are taken into account when interpreting the results (Zech, 1997). Under the average European climatic conditions the decomposable carbon in SOC is 0.2 %-0.6 %, corresponding to 8 to 24 t/ha (Körschens, 1997). By using methods of calculating the balance of humus we are given an opportunity to control the SOM content in arable soils in order to achieve higher yields and simultaneously avoid environmental pollution. In the trial, the method of calculating the balance of humus determined by Diez and Krauss was used (Diez and Krauss, 1992); this method, which we named the "Swiss method", is believed to be an appropriate method for the central Slovenian climatic conditions.
The aim of our study was to examine, with the application of the "Swiss method", the impact of organic and mineral fertilization on the humus content in the soil according to particular crop rotation at two different locations with a specific soil type and particular climatic conditions.
2 MATERIALS AND METHODS
2.1 Experimental layout
Two long-term experiments were established at IOSDV Jable and IOSDV Rakičan in 1993.
The trial was set up as a permanent experiment related to crop rotation with ten different fertilization combinations as a block trial with three repetitions. First, the trial area was divided into three plots, on which each year crops were sown in the following order: corn, winter wheat, barley/oats. Each plot was further divided into two subplots, on which different systems of fertilization with organic management were studied. Each subplot thus represented five variants differing according to the rate of fertilization with mineral nitrogen in the three repetitions. The basic plot size was 30 m2 (5 x 6 m). Ten different treatments were included in the investigation:
Table 1:
2.2 Humus balance calculation method
The method of calculating the balance of humus was determined by Diez and Krauss (Diez and Krauss, 1992). We named it the "Swiss method". The annual balance (Hn) is calculated on the basis of the ploughed-in quantity of organic matter (manure (Zd), straw (Ze ), catch crop (Ze), harvest residues (Ze)) with the corresponding humification coefficient (HKd, HKe), taking into account the quantity of humus in the soil (H) with the appropriate mineralization coefficient (HMk). Results are given in the Corg value (t/ha), which is calculated on the basis of humus content (t/ha) multiplied by factor 0.58. The equation for calculating the balance of humus is shown in Table 2.
-	management system with no organic fertilizers (system A) and two different mineral rates (N0, N3),
-	management system with farmyard manure ploughing in (system B) and four different mineral N rates (N0, N1, N2, N3),
-	management system with straw ploughing in (system C) and four different mineral N rates (N0, N1, N2, N3).
Fertilizing plan for the nutrition of arable crops is shown in Table 1. At the harvest time, yield and straw quantities were measured for each plot. After harvesting every year soil samples from each plot were taken at a depth of 0-25 cm for further analysis.
In the year of establishment of the experiment (1993) the soil analysis were conducted at the laboratories UFZ LeipzigHalle, Germany (Tajnšek, 2003); the Corg content was determined according to ISO 10694, 1996-08. In the calculation of humus balance we considered this initial value of Corg in 1993 content, while presented results are for the period 1998-2008.
Statistical analysis was conducted with the Statgraphics Plus 4.0 program. Multifactor ANOVA was used in order to analyze the effect of different management systems on the humus content in the soil. Differences among treatments were detected by Duncan's Multiple Range Test (p < 0.05).
Management systems, mineral N fertilization with regard to the crop, the average amount of mineral N in the three-year crop rotation (Miner. Naver) at the IOSDV Jable and IOSDV Rakičan locations for ten treatments.
		Miner. N rates	Maize (kg/ha N)	Wheat (kg /ha N)	Barley/ Oats (kg /ha N)	Miner. N L ^ aver. (kg /ha N)	Treat.
m	No organic fertilizers		/	/	/		
e st y		NO	0	0	0	0	AN0
S		N3	300	195	165	220	AN3
B	Farmyard manure ploughing in (t/ha)		30 t/ha farmyard manure	/	/		
m te st y S		NO N1 N2 N3	0 100 200 300	0 65 130 195	0 55 110 165	0 73 147 220	BN0 BN1 BN2 BN3
C	Straw/catch crop ploughing in (t/ha)		Barley/oats straw + fodder radish	Maize straw	Wheat straw		
m te st y S		NO N1 N2 N3	0 100 200 300	0 65 130 195	0 55 110 165	0 73 147 220	CN0 CN1 CN2 CN3
Table 2: The equation for the humus balance calculation with the corresponding parameters for each of the three management systems (system A, B, C) (modified by Diez and Krauss, 1992).
Eq:
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System ' A	(roots1	x	0.02)	-	(HAn-1	x	0.01)	= HAn
System	(roots	x	0.02)	+ (farm. x 0.25) -	(HBn-1	x	0.01)	= HBn
B				manur e2				
	(roots	x + x + x	0.02)					
System ' C	(straw (fodder radish3		0.15) 0.1)		(HCn-1	x	0.01)	= HCn
'The amount of straw t SS/ha x roots/straw ratio coefficient (0.5).
2The amount of farmyard manure 7.5 t SS/ha is considered only for maize (in the years 1999, 2002, 2005, 2008). 3Ploughing in of fodder radish as a catch crop is considered only after barley/oats (in the years 1998, 2001, 2004, 2007).
+
X
X
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2.3 Weather and soil conditions
For the chemical and physical properties of the soil measured at the beginning of the trial cf. Tajnšek (2003). The soil type at the IOSDV Jable location (46 ° 8'N, 14 ° 34'N, 305 m above sea level) is Umbric Planosols (Plu), while soil texture is determined as silt loam. The soil type at the IOSDV Rakičan location (46°38'N, 14°11'N, 184 m above sea level) is Eutric Fluviosol (ELe), while soil texture is determined as sandy silt.
IOSDV Jable is located in the subalpine zone, where prolonged droughts are rare even in the summer, let alone in the winter and autumn. Its reference weather station is Brnik. In the period 1961-1990, the average annual temperature was 8.3 °C and ranged from 7.3 °C to 9.8 °C. The long-term average precipitation during the period 1961-1960 amounted to 1384 mm in the 987 mm to 1770 mm interval. During the trial period (1998-2008), the average annual temperature was more than 1°C higher compared to the long term average. In the years 2000, 2002, 2003 and 2008, the average annual
temperature ranged from 9.7 °C to 10.2 °C. In the years studied, the average annual precipitation was 1323 mm; in 2004, 2005, 2008, on the other hand, it was 8-17 % higher in comparison with the long term average.
IOSDV Rakičan is located on the south-western edge of the Pannonian climate zone. Its reference weather station is Murska Sobota. In the period 1961-1990, the average annual temperature was 9,2 °C, ranging from 8.2 °C to 10.1 °C. The long-term average precipitation during the period 1961-1990 was 814 mm in the 563 mm to 1064 mm interval. From 1998 to 2008, the average annual temperature was 1.3 °C higher in comparison with the long-term average temperatures. The hottest years were 2000, 2002, 2007 and 2008, with average annual temperatures above 11 °C. In the years studied, the average annual precipitation was 747 mm; in 2003, however, it was approximately 30 % smaller compared to the long-term average precipitation.
The average annual temperature in the period 1998-2008 and the long-term average temperature (1960-1990) for the IOSDV Jable and IOSDV Rakičan locations
14 12
10 J o o
.----_........a...-...-.. "... ja...,
8
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~ 6
4 2
■ 98-08 Brnik
-61-90 Brnik
o 98-08 Murska Sobota .....61-90 Murska Sobota
O^ Ov3	^
Years
0
Figure 1: Annual precipitation for the period 1998-2008 and the long-term average precipitation (1961-1990) for the IOSDV Jable (weather station Brnik) and IOSDV Rakičan (weather station Murska Sobota) locations (above) and the average annual temperature for the period 1998-2008 and the long-term average temperature (1960-1990) for both locations (below).
3 RESULTS AND DISCUSSION
3.1 IOSDV Jable
Results showing the Corg content at the IOSDV Jable location for the period 1998-2008 and the average Corg content for the period of 11 years are given in Table 3. The initial value of Corg at the beginning of the trial in 1993 was 55.48 t/ha Corg. Over the period 1998-2008,
the impact of organic and mineral fertilization on the content of Corg was confirmed. In system A, fertilizing with mineral nitrogen significantly affected the increase of the Corg content. On average, the Corg content rose from 50.6 t/ha Corg in an AN0 control to 52.2 t/ha Corg in AN3, which corresponds to 3.2%.
Table 3: The Corg content (t/ha) during the period 1998-2008 and the average Corg content (t/ha) for the same period for ten treatments (including three different management systems: A, B, C and nitrogen fertilization: N0, N1, N2, N3) at IOSDV Jable at a depth of 0-25 cm, calculated by the "Swiss method".
IOSDV Jable
Corg (t/ha)
Tre	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007	2008	Aver
at.	Bar.	Mai.	Whe.	Bar.	Mai.	Whe.	Oats	Mai.	Whe.	Oats	Mai.	11yr.
AN0	53.02	52.48	51.99	51.48	50.95	50.50	50.12	49.61	49.13	48.43	48.43	50.60
	a*	a	a	a	a	a	a	a	a	a	a	a
	±0.08	±0.10	±0.12	±0.11	±0.12	±0.12	±0.14	±0.19	±0.18	±0.18	±0.20	±0.14
AN3	53.70	53.54	53.15	52.69	52.39	52.02	51.77	51.67	51.31	51.29	51.02	52.23
	b	b	b	b	b	b	b	b	b	b	b	b.....
BN0	54.17	54.74	54.23	53.72	54.31	53.84	53.43	53.99	53.48	53.22	53.80	"53.91"
	c	d	d	d	d	d	d	d	d	d	d	d
BN1	54.44	55.13	54.67	54.17	54.83	54.40	54.05	54.71	54.27	54.15	54.79	54.51
	d	e	e	e	ef	e	e	e	e	e	e	e
BN2	54.60	55.39	54.95	54.50	55.19	54.78	54.45	55.15	54.75	54.63	55.38	54.89
	de	ef	ef	f	fg	f	ef	ef	ef	e	ef	ef
BN3	54.70	55.57	55.17	54.75	55.50	55.10	54.79	55.65	55.26	55.28	56.03	55.25
	e	f	f	f	g	f	f	f	f	f	g	f
CN0	54. f 3	53.90	54.84	53.22	53.04	52.70	52.64	52.78	52.36	52.57	52.53	"53.04"
	c	c	c	c	c	c	c	c	c	c	c	c
CN1	55.11	55.09	54.84	54.58	54.55	54.29	54.46	55.05	54.77	55.33	55.48	54.87
	f	e	ef	f	de	e	ef	e	ef	f	fg	ef
CN2	55.44	55.98	55.77	55.55	55.88	55.65	55.84	56.73	56.55	57.47	57.89	56.25
	g	g	g	g	h	g	g	g	g	g	h	g
CN3	55.74	56.69	56.47	56.29	56.88	56.63	56.88	57.68	57.51	58.51	59.10	57.13
	h	h	h	h	i	h	h	h	h	h	i	h
*a-i - The same letter in the column indicates that there is no significant difference among treatments (Duncan multiple range test. p<0.05).
In the system with farmyard manure ploughing in (system B), the Corg content was, in all treatments, significantly higher compared to the Corg content in system A. In 2001 and 2003, fertilization with a higher amount of mineral nitrogen (BN2, BN3) demonstrated a positive impact on the increase of the Corg content; in 2007 and 2008, on the other hand, only the treatment with the highest amount of mineral nitrogen (BN3) proved to have the same effect. In other years, the mineral nitrogen fertilization influenced the Corg content; the differences among treatments could, however, not be statistically confirmed. The Corg content in system B increased by an average of 3.3 t/ha Corg to 4.7 t/ha Corg compared to the average Corg content in AN0.
In the system with ploughing in of straw and catch crops (system C), the Corg content was, in all treatments, significantly higher compared to the Corg content in the AN0 control. Unlike system B, differences among treatments (CN0, CN1, CN2, CN3) in system C were
statistically confirmed in all the studied years. Increasing the amount of mineral nitrogen resulted in a higher Corg content, in accordance with Haynes and Körschens (Haynes and Naidu, 1998; Körschens, 1997). The Corg content in system C increased by an average of 2.4 t/ha Corg to 6.5 t/ha Corg, which equals the 4.8-12.9 % rise compared to the average value of Corg content in AN0.
After 11 years, the Corg content in system A decreased -in the AN0 control by 4.6 t/ha Corg (8.6%), in AN3, where the mineral nitrogen was added, by 2.7 t/ha Corg, corresponding to 5.0%. Fertilization with the highest amount of mineral nitrogen resulted in a minor reduction of the Corg content compared to the AN0 control (Figure 2). The results suggest that the degree of mineralization in system A is greater than the degree of humification.
O 1 /T
Plot of Fitted Model
m —
o O
60 58 56 54 52 50 48
Treatment -B- AN0
- AN3
- BN0
SC BN1 BN2 i BN3 CN0 □ CN1
- CN2
C CN3
1998 1999 2000 2001
2002 2003 2004 2005 2006 2007 Year
2008
Figure 2: The Corg content (t/ha) in the period 1998-2008for ten different treatments at the IOSDV Jable location.
In system B, the Corg content in the treatment without the mineral nitrogen (BN0) decreased by 0.4 t/ha Corg (0.7%) compared to the initial value of the Corg content in the year 1998. By increasing the amount of mineral nitrogen, the Corg content rose by 0.4 t/ha Corg in BN1, by 0.8 t/ha Corg in BN2 and by 1.3 t/ha Corg in BN3. In comparison with the initial value in 1998, the Corg content in system C in 2008 was higher only in the treatments where mineral nitrogen was added; in CN1, the Corg content increased by 0.4 t/ha Corg, in CN2 by 2.5 t/ha Corg and in CN3 by 3.4 t/ha Corg.
Each year, the maximum Corg content was reached in the treatment CN3. The average value of difference of the Corg content between CN3 and AN0 throughout the eleven-year period was 6.6 t/ha Corg, varying from 2.7 t/ha Corg in 1998 to 10.6 t/ha Corg in 2008.
3.2 IOSDV Rakičan
Results for the Corg content at the IOSDV Rakičan location for the period 1998-2008 and the average Corg content for the eleven-year period are given in Table 4. The initial value of Corg in 1993 was 37.27 t/ha Corg. In the years studied (1998-2008), the impact of organic fertilization on the Corg content was confirmed. In system A, fertilizing with mineral nitrogen (AN3) increased the Corg content; the difference between treatments could, however, not be statistically confirmed. On average, the Corg content in AN3 increased to 35.47 t/ha, which is 2.8% more than the average value of the Corg content in the AN0 control.
In system B, the Corg content was, in all treatments, significantly higher compared to the AN0 control. Despite the differences in absolute values, we were unable to confirm statistically significant differences among treatments with a different degree of added
mineral nitrogen (BN0, BN1, BN2, BN3). The Corg content in system B increased by an average of 4.1 t/ha Corg to 5.2 t/ha Corg, which was 11.9-15.1 % higher compared to the average value of Corg content in AN0.
In the straw ploughing in system (system C), the Corg content was higher in all treatments with regard to the Corg content in AN0. Fertilization with the lowest amount of mineral nitrogen (CN1) had insignificantly increased the Corg content in the years until 2005; from this year on, however, the impact was statistically significant. Among the treatments where medium (CN2) and the highest (CN3) amount of nitrogen was applied, there were no statistically significant differences. The Corg content in system C increased by an average of 3.8 t/ha Corg to 6.9 t/ha Corg compared to the average value of the Corg content in AN0, i.e. by 10.9% to 19.8%.
At IOSDV Rakičan, the Corg content in system A decreased after 11 years; in the AN0 control by 2.4 t/ha Corg (6.6 %), in AN3 where mineral nitrogen was added by 1.2 t/ha Corg, which equals to 3.4.0 %. These results are comparable to the results measured at IOSDV Jable (Figure 3). By increasing the amount of mineral nitrogen in system B, the Corg content increased by 3.5 t/ha Corg (BN1), by 4.1 t/ha Corg (BN2) and by 4.2 t/ha Corg (BN3). According to the Corg content in 1998 in system C, the Corg content increased in all treatments; in CN0 by 2.0 t/ha Corg, in CN1 by 4.0 t/ha Corg, in CN2 by 4.7 t/ha Corg and in CN3 by 5.6 t/ha Corg.
Each year, the maximum Corg content was reached in CN3. The average value of difference of the Corg content between CN3 and AN0 throughout the eleven-year period was 6.9 t/ha Corg, varying from 2.9 t/ha Corg in 1998 to 10.8 t/ha Corg in 2008
Table 4: The Corg content (t/ha) during the period 1998-2008 and the average Corg content (t/ha) for the same period for ten treatments (including three different management systems: A, B, C and nitrogen fertilization: N0, N1, N2, N3) at IOSDV Rakičan at a depth of 0-25 cm, calculated by the "Swiss method".
IOSDV Rakičan
Corg (t/ha)
Tre	1998	1999	2OOO	2OO1	2OO2	2003	2004	2005	2006	2007	2008	Aver
a.	Bar.	Mai.	Whe.	Bar.	Mai.	Whe.	Oats	Mai.	Whe.	Oats	Mai.	11yr.
ANO	35.58	35.40	35.10	34.78	34.97	34.62	34.34	34.17	33.84	33.46	33.23	34.50
	a	a	a	a	a	a	a	a	a	a	a	a
	±0.18	±0.26	±0.28	±0.18	±0.47	±0.50	±0.54	±0.59	±0.61	±0.63	±0.72	±0.28
AN3	36.06	36.05	35.85	35.69	35.70	35.48	35.33	35.24	35.09	34.82	34.83	35.47
	a	a	a	a	a	a	a	a	a	a	a	b
BNO	37.10	38.24	37.89	37.59	39.01	38.66	38.39	39.63	39.34	38.96	40.1	38.63
	b	bc	bc	b	b	b	b	bc	bc	bc	bc	cd
BN1	37.39	38.68	38.39	38.15	39.66	39.31	39.08	40.3	40.06	39.74	40.92	39.24
	b	cd	bcd	b	bc	bc	bc	bcd	bcd	bc	bcd	de
BN2	37.39	38.67	38.40	38.21	39.86	39.59	39.40	40.74	40.53	40.19	41.52	39.49
	b	cd	bcd	b	bc	bc	bcd	cde	bcd	bcd	cd	e
BN3	37.56	38.89	38.64	38.48	40.02	39.78	39.57	40.94	40.78	40.45	41.74	39.72
	b	cd	cde	b	be	be	bed	cde	cd	bed	cd	e
CNO	37.17	37.83	37.61	37.59	38.66	38.43	38.57	38.83	38.61	38.48	39.19	38.26
	b	b	b	b	b	b	bc	b	b	b	b	c
CN1	37.67	38.48	38.41	38.59	39.98	39.85	40.18	40.78	40.83	40.90	41.64	39.76
	b	bc	bcd	bc	bc	bc	cd	cde	cd	cd	cd	e
CN2	38.22	39.07	39.15	39.55	40.70	40.70	41.02	41.75	41.93	42.09	42.92	40.65
	c	cd	ef	cd	cd	cd	de	de	de	de	de	f
CN3	38.49	39.35	39.44	39.98	41.52	41.56	41.86	42.61	42.88	43.07	44.12	41.35
	c	d	f	d	d	d	e	e	e	e	e	f
*a-i — The same letter in the column indicates that there is no significant difference among treatments (Duncan multiple range test. p<0.05).
Plot of Fitted Model
tg —
o O
53 49 45 41 37 33 29
L o - 0 g in H —	o- ~ O o o g: i l * 1 * !
"n ■ - ■-S-ft-	S v b « » er-
	
Treatment -H- ANO
- AN3
- BNO
S BN1 BN2 i BN3 CNO □ CN1
- CN2
C CN3
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
Figure 3: The Corg content (t/ha) in the period 1998-2008for ten different treatments at the IOSDV Rakičan location.
According to Table 5, a greater influence of management systems and mineral N fertilization could be reached at IOSDV Rakičan. As the average absolute value of difference of the Corg content for all treatments amounted to 3.5 t/ha and was almost two times higher
as at IOSDV Jable, it is possible to conclude that soil with a lower clay content could be more influenced by different management usage.
Table 5: Balance of Corg content during the eleven-year period (Corg in 2008 minus Corg in 1998) and the average absolute value of the Corg content (xaver) (t/ha) at the IOSDV Jable and IOSDV Rakičan locations.
	IOSDV Jable	IOSDV Rakičan
Treatment	|Corg2008-Corg1998|	|Corg2008-Corg1998|
	(t/ha)	(t/ha)
AN0	I -4 61	|-2.4|
AN3	I -2 71	| -1.21
BN0	I -0 41	13.01
BN1	10.41	|3.5|
BN2	10. 81	|4.1|
BN3	11. 31	|4.2|
CN0	I -1. 61	12.01
CN1	10.41	14.01
CN2	12. 51	|4.7|
CN3	13.41	|5.6|
Xaver	1.8	3.5
4 CONCLUSIONS
During eleven-year period the application of organic fertilizers in the form of farmyard manure or straw significantly influenced the Corg content at two long-term experiments, with different soil and climatic conditions. At IOSDV Jable, within system B, the Corg content increased by an average of 3.3 t/ha Corg to 4.7 t/ha Corg compared to the Corg content in the AN0 control. Moreover, in the system with ploughing in of straw and catch crops (system C), the Corg content also increased by an average of 2.4 t/ha Corg to 6.5 t/ha Corg. At IOSDV Rakičan, within system B, the Corg content increased by an average of 4.1 t/ha Corg to 5.1 t/ha Corg compared to the Corg content in the AN0 control, while, in system C, the Corg content increased by an average of 3.8 t/ha Corg to 6.8 t/ha Corg. A significant impact of mineral N on the Corg content was determined in
systems A and C at both locations, while in system B this impact could not be proven.
After 11 years, the Corg content in system with no organic fertilizers (system A) decreased irrespective of the mineral N fertilization at both locations. At IOSDV Jable, a small decrease of the Corg content was measured in BN0, while all other treatments at IOSDV Jable and IOSDV Rakičan resulted in an enlarged Corg content. The average absolute value of difference between the Corg content in 2008 and 1998 for all treatments at IOSDV Rakičan was almost two times higher as at IOSDV Jable. According to these results as well as according to other authors' statements we determined that soil with a smaller clay content shows the greatest dependence on the selected management.
5 ACKNOWLEDGEMENT
This work is part of the "Genetics and modern 0077) funded by the Slovenian Research Agency technologies of agricultural plants" programme (P4- (ARRS).
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