SC THE EFFECT OF TILLAGE SIMPLIFICATIONS AND MINERAL FERTILISATION LEVEL ON THE NUMBER AND DISTRIBUTION OF WEED SEEDS IN SOIL

In the present paper, results of a study on the effect of a reduction in the number of ploughings in a crop rotation on the seed weed bank in the soil are presented. The study was carried out in the second and fourth year of a crop rotation (potato- spring wheat- pea- winter wheat). A reduction in the number of ploughings to three in the crop rotation decreased weed infestation of the plough layer, whereas when only one ploughing was made there was clearly more weed diaspores in the soil than after plough tillage. In the first period of the study, the mineral fertilisation level did not differentiate the weed seed bank in the soil, whereas after the end of the rotation its significant increase was noted as a result of more intensive fertilisation. In all the experimental treatments, diaspores of Chenopodium album , Viola arvensis , Galinsoga sp. and Apera spica-venti occurred in greatest numbers.


INTRODUCTION
In connection with the need to limit production costs in agriculture, different simplifi cations in soil tillage are used.They consist most frequently in reducing the depth and frequency of ploughings, replacing them by other less energy-consuming treatments, including direct sowing.Nevertheless, studies conducted so far do not give a full and unequivocal answer to the question how different plough tillage simplifi cations affect possible weed infestation of soil.Therefore, this study was conducted; its aim was to determine the condition and level of weed infestation of the cultivated soil layer under the infl uence of a reduced number of ploughings in a fourfi eld crop rotation system and with differentiated mineral fertilisation levels.

MATERIALS AND METHODS
The fi eld experiment was carried out in the years 1998-2002 at the Czesławice Experimental Farm, belonging to the University of Natural Sciences in Lublin.The fi eld experiment was set up in a splitblock design, with four replications, on grey-brown podzolic soil formed from loess with the granulometric composition of clayey silt (36% of fi ne particles).The soil in the experiment was characterised by a slightly acid reaction (pH in 1 mol KCl dm -3 -6.5-6.6), humus content of 16.3g kg -1 of soil and a high abundance of available phosphorus, potassium and magnesium.
The fi eld studies covered the fi rst rotation of the four-fi eld crop rotation beginning with the following crop sequencing of all the plants: potato-spring wheatpea -winter wheat.For each plant, three tillage methods and two mineral fertilisation levels were used: I. Tillage methods A -traditional (7 ploughings per rotation), B -reduced (3 ploughings per rotation), C -reduced (1 ploughing per rotation); II.Mineral fertilisation levels a. 167.5 kg NPK and b. 251.2 kg NPK on an annual average basis per rotation.
Ploughings were replaced mainly by soil cultivating or disking.A detailed list of measures performed in particular tillage treatments is shown in Table 1.
The following herbicides were applied in particular crop plants: in potato -Dispersion Afalon 450SC 2L ha -1 (450 g of linuron in 1L of the herbicide); in spring wheat -Puma Uniwersal 069 EW -1L ha -1 (69 g of fenoxaprop-P-ethyl with a 75g addition of mefenpyr-diethyl in 1L of the herbicide) and Aminopielik D 450SL -3 L ha -1 (417.5 g 2.4D, 32.5 g of dicamba in the form of dimethylamine salts in 1L of the herbicide); in pea -Stomp 330EC 4 L ha -1 (330g of pendimethalin in 1L of the herbicide); in winter wheat -Puma Uniwersal 069 EW -1.2 L ha -1 (69g of fenoxaprop-P-ethyl with a 75g addition of mefenpyr-diethyl in 1L of the herbicide) and Aminopielik D 450SL -3 L ha -1 (417.5 g 2.4D, 32.5 g of dicamba in the form of dimethylamine salts in 1L of the herbicide).
Soil samples collected using a cylinder with a diameter of 7.8 cm from three soil layers, notably: 0-5 cm, 5-15 cm and 15-30 cm, after the harvesting of particular plants, were the object of detailed examination.The soil samples for each treatment were a mixed sample from the replications of each tillage method for particular plants of the crop rotation.In order to separate weed seeds from soil solid particles, the samples were washed with water on sieves with 0.25 mm mesh.They were then dried at a temperature of 40 o C and weed fruits and seeds were picked out manually (using forceps) from them.In this study, only properly developed and fi lled weed fruits and seeds, hence presumably able to germinate, were taken into consideration.Species names of weed seeds followed M i r e k et al. [1995].

RESULTS AND DISCUSSION
The study conducted in the years 2000 and 2002 (in the second and fourth year of the crop rotation) showed that the applied tillage simplifi cations and mineral fertilisation level had no signifi cant effect on the species composition of weed seeds in the 0-30 cm soil layer (Tab. 2 and 3).The determinations made after the end of the rotation only demonstrated substantial impoverishment of the species composition of weed diaspores (Tab.3).From among previously noted species, seeds of Fallopia convolvulus, Sonchus asper, Vicia tetrasperma, Thlaspi arvense, Myosotis arvensis and Polygonum persicaria were not found, and caryopses of Avena fatua, which had not been previously noted, were determined.In both years of the study, irrespective of the tillage method, slightly more weed species were noted in the intensively fertilised treatments.A signifi cant decrease in the number of weed diaspores in the soil in 2002 compared to 2000 is also worth noting.
The applied tillage modifi cations signifi cantly differentiated the seed weed bank in the soil (Tab.4).In both years of the study, the smallest number of weed seeds, both the total number and the number of dominant species' seeds, was found after the number of ploughings was reduced to 3 in the crop rotation (B), it was signifi cantly larger after typical tillage (A -7 ploughings in the crop rotation), and the largest one when only one ploughing was made in the crop rotation (C).
More intensive fertilisation increased significantly the total weed seed bank and the number of dominant species' seeds only in 2002, thus, after the end of the crop rotation (Tab.4).In the present study, no signifi cant interaction was found between the tillage system and the fertilisation level with respect to the weed seed bank in the soil.
Also, the applied tillage simplifi cations and mineral fertilisation level had no signifi cant impact on the distribution of weed seeds in the analysed soil layers.Only the smallest number of diaspores in the surface layer was noted most frequently, and its increase together with the increase of the depth.
The species composition of weeds in particular experimental treatments was similar.In 2000 only 8 species from the weed species found occurred in all the tillage and fertilisation treatments.But in 2002 as many as 12 species were common out of 18 species found.The dominant species were as follows: Chenopodium album, Viola arvensis, Apera spica-venti and Galinsoga sp.Chenopodium album seeds occurred in greatest numbers among them.They accounted for 60% of the total number of all identifi ed diaspores.
To sum up the obtained results, it should be stressed that the introduced simplifi cations did not have an unequivocal effect on the weed seed bank in the soil, since it was found that a reduction in the number of ploughings to three in the crop rotation decreased the seed bank, and it was the application of only one ploughing which clearly increased this trait compared to typical tillage (7 ploughings in the crop rotation).Such fi ndings are only partially consistent with the results of W i t k o w s k i ( 1998   Species composition, number and distribution of weed seeds in three soil layers in pcs•m-2 (mean for crop rotation in 2002).
a signifi cant increase in the number of weed seeds on the soil surface and a marked decrease in their number in the deeper layers under the infl uence of tillage simplifi cations, in particular the application of direct sowing.The infl uence of the mineral fertilisation level was evident only in the second period of the study in which a signifi cant increase in the seed bank in the soil was noted in the more intensively fertilised treatments.The absence of research in this area prevents a confrontation of results.The studies of K ę s i k (1980), B l ec h a r c z y k et al. (2000) as well as P a w ł o w s k i and W e s o ł o w s k i (1990) demonstrate that more intensive fertilisation is one of factors inhibiting weed infestation of a crop canopy.
When analysing the species composition of weed seeds in the soil, it should be stated that it is typical for loess-formed soils (W e s o ł o w s k i , 1986) and plants cultivated in a crop rotation system (K a p e l u s z n y and J ę d r u s z c z a k , 1992).The dominant species were Chenopodium album, Viola arvensis, Apera spica-venti and Galinsoga sp, which accounted for over 80% of the total bank of weed diaspores.Similarly, B o c h e n e k (1992), R a d e c k i and C i e s i e l s k a (2000) also report that only several weed species are always predominant in weed communities found in the  (1988) who report that the introduction of herbicides in the protection of crop canopies signifi cantly reduces the weed seed pool in the soil and impoverishes the species composition of the community.

CONCLUSIONS
1.A comparison of results of determinations from the end of the crop rotation and its beginning showed that a very large decrease in the number of weed diaspores in the soil occurred in all the experimental treatments.2. A reduction in the number of ploughings to three in the crop rotation decreased weed infestation of the plough layer, whereas giving only one ploughing clearly increased the weed diaspore bank in the soil compared to typical tillage.
3. In the fi rst period of the study, the mineral fertilisation level did not differentiate the weed seed bank in the soil.But there was its signifi cant increase after the end of the rotation as a result of more intensive fertilisation.4. Diaspores of Chenopodium album, Viola arvensis, Galinsoga sp. and Apera spica-venti occurred in greatest numbers in the examined loess soil layer.
R a d e c k i , 1986; D z i e n i a and S o s n o w s k i , 1991; (G a w r o ń s k a -K u l e s z a , 1997; M a l i c k i et al. 1997; K o r d a s , 1999).The use of such simplifi cations may however lead to an increase in weed infestation of a crop canopy and accumulation of weed diaspores in the soil (D w o ř a k , 1987; P a p a y et al. 1994; S k r z y p c z a k et al. 1995); F e l d m a n et al. 1996; W i t k o w s k i , 1998; D o r a d o et al. 1999; D z i e n i a et al. 2003.
), C a r d i n y et al.(1991), F e l d m a n a et al.(1992), P a p a y et al.(1994), C o u s e n s and M o s s (1990) as well as W e s o ł o w s k i and B u j a k(2006)  in whose studies the application of tillage simplifi cations, mainly direct sowing, resulted in an increase in the weed seed bank.In turn, W r z e s i ń s k a et al. (2004) as well as O p i c (1996) noted a decrease in the weed seed bank under the infl uence of no-plough tillage or the application of direct sowing.But D w o ř a k (1987) reports that a decrease in tillage depth in crop sequencing did not result in an increase of potential weed infestation.In our study, no great difference was found in the number of weed diaspores in the analysed soil layers.But W r z e s i ń s k a et al. (2004), O p i c (1996), O r z e c h et al. (2006), Z a w i e j a et al. (2000), D o r a d o et al. (1999), U n g e r et al. (1999: skimming (10-12 cm) + harrowing (2 times) + manure + fall ploughing (25-30 cm) summer/autumn: cultivating (10-12 cm) + harrowing + manure + fall ploughing (25-30 cm) summer/autumn: disking (10-12 cm) + harrowing + manure + fall ploughing (25-30 cm) spring: harrowing + cultivating (10-15 cm) + harrowing + planting Spring wheat summer/autumn: fall ploughing (18-20 cm) summer/autumn: cultivating (10-12 cm) summer/autumn: harrowing (8-10 cm) spring: harrowing + cultivating (10-15 cm) + harrowing + sowing + harrowing Pea summer/autumn: skimming (10-12 cm) + harrowing (2 times) + manure + fall ploughing (18-20 cm) summer/autumn: cultivating (10-12 cm) + harrowing + fall ploughing (shallow to 15 cm) summer/autumn: disking (10-12 cm) + harrowing + subsoiling (35-40 cm) spring: harrowing + cultivating (10-15 cm) + harrowing + sowing + harrowing Winter wheat summer/autumn: skimming (10-12 cm) + harrowing (2 times) + pre-sow ploughing (18-20 cm) + harrowing + sowing + harrowing summer/autumn: without after-harvest cultivation -only hallow pre-sow ploughing (to 15 cm) + harrowing + seeds in 0-30 cm soil layer in pcs m -2 (mean per crop rotation).soil.A substantial decrease in the seed weed bank in the soil and a reduction in their species composition noted after the end of the rotation, compared to the fi rst period of the study, resulted from the application of intensive chemical protection of canopies of particular plants.It fi nds confi rmation in earlier studies of D w o ř a k and K r e j c i r (1980), R o b e r t s (1981), A d a m i a k et al.