WEED INFESTATION OF A SPRING WHEAT (Triticum aestivum L.) CROP UNDER THE CONDITIONS OF PLOUGH AND PLOUGHLESS TILLAGE

A field experiment was conducted in the period 20072009 in the Uhrusk Experimental Farm (Lublin region) belonging to the University of Life Sciences in Lublin. Different tillage systems – plough and ploughless tillage – were the experimental factors. In the plough tillage system, tillage involved skimming done after the harvest of the forecrop and autumn ploughing. In the ploughless tillage system, only the herbicide Roundup 360 SL (active substance – glyphosate) was applied after the harvest of the forecrop. In both tillage treatments, spring tillage involved field cultivating and the use of a tillage assembly consisting of a cultivator, cage roller, and harrow. The present experiment evaluated weed infestation of the crop expressed by the number and air-dry weight of weeds and their species composition. Under the conditions of ploughless tillage, air-dry weight of weeds in the spring wheat crop was shown to increase significantly compared to plough tillage. The tillage systems under comparison did not differentiate the number of weeds per 1 m. Spring wheat sown using plough tillage was colonized most extensively by the following weed species: Avena fatua L., Stellaria media (L.) Vill., Galium aparine L., Amaranthus retroflexus L., Chenopodium album L., and Consolida regalis Gray. In the ploughless tillage treatments, the following weeds were predominant: Stellaria media (L.) Vill., Avena fatua L., Fallopia convolvulus (L.) A. Löve, Papaver rhoeas L., Amaranthus retroflexus L., Galium aparine L., and Chenopodium album L.


INTRODUCTION
The weed infestation level in cereal crops is affected by many factors, among which the most important role is attributed to the soil diaspore bank, agricultural practices used, and habitat conditions (K r a s k a and P a ł y s , 2006; S e k u t o w s k i and R o l a , 2006). The literature of the subject shows that fruits and seeds in the soil are a potential source of crop weed infestation, which is reflected in weed infestation of the crop (W e s o ł o w s k i and W o ź n i a k , 2001; F e l e d y n -S z e w c z y k and D u e r , 2007). The weed infestation level is also dependent on the tillage system. W e b e r and H r y ń c z u k (2005) showed that reduced tillage increased weed infestation of a winter wheat crop compared to conventional tillage and direct drilling or sowing. Similar conclusions were also made by G a w ę d a (2007). She showed an increase in the weed infestation rates under the conditions of ploughless tillage compared to plough tillage. In the study of W o ź n i a k (2010), ploughless tillage also had an effect on the increase in the number and weight of weeds in comparison with plough tillage. In turn, plough tillage promoted the increase in the number of weed species compared to ploughless tillage. S e k u t o w s k i and R o l a (2006) draw attention to the increase in the number of fruits and seeds in the soil under the conditions of ploughless tillage, whereas D z i e n i a and D o j s s (1999) to their distribution in the soil. As shown by research, in ploughless tillage systems diaspores accumulate primarily in the topsoil, hence when they germinate they affect weed infestation of the crop plant.
The aim of the present study was to compare the values of the weed infestation parameters (number of weeds per 1 m 2 , air-dry weight of weeds in g x m -2 , and species composition) in a spring wheat crop sown using plough and ploughless tillage systems.

MATERIALS AND METHODS
A field experiment was conducted in the period 2007-2009 in the Uhrusk Experimental Farm (Lublin region) belonging to the University of Life Sciences in Lublin. It was set up on mixed rendzina soil with the composition of light, slightly sandy loam and was carried out in 3 replicates on 24 m 2 plots. The experiment evaluated weed infestation of a crop of spring wheat Triticum aestivum L. sown using plough and ploughless tillage systems. Plough tillage involved skimming (harrowed) done after the harvest of the forecrop (pea) and autumn ploughing. Ploughless tillage was limited to a single application of the herbicide Roundup 360 SL (active substance -glyphosate) -4 lxha -1as a post-harvest treatment. In both tillage treatments, spring tillage involved field cultivating and the use of a tillage assembly consisting of a cultivator, cage roller, and harrow. Weed control in the wheat crop under both tillage systems was reduced to harrowing the crop once at the tillering stage.
Weed infestation of the crop was assessed using the botanical gravimetric method. This method consists in the determination of the species composition of weeds as well as their number and air-dry weight per 1 m 2 of the plot. This sampling area was randomly selected (twice) using a frame with the dimensions of 1 m x 0.5 m. The determination of air-dry weight of weeds consists in collecting all weeds from within the frame, removing their root systems and placing the weeds in a well-aired and dry place until the time when a constant weight is obtained. In the present study, the number and air-dry weight of weeds as well as weed species composition were determined at the dough stage of maturity of the wheat crop.

RESULTS
The growing seasons in which the present study was conducted differed significantly in terms of total rainfall (Table 1). During the period from sowing of spring wheat to its harvest, i.e. from April to August, the rainfall level was by far the highest in 2007 (467.4 mm), total rainfall was lower in 2009 (380.5 mm), while it was the lowest in 2008 (312.7 mm). It can be presumed that these conditions affected the weed infestation parameters, in particular the number of weeds and their air-dry weight. The data contained in Table  2 show that the highest amount of weeds (on average 137.9 per 1 m 2 ) occurred in 2007, i.e. the year with the highest total rainfall, this number was lower in 2009 (80.8 per 1 m 2 ), and the lowest (51.5 per 1 m 2 ) in the year 2008 with the lowest rainfall level. High rainfall increased the number of weeds per 1 m 2 , in particular under the conditions of plough tillage. In turn, when analysing the number of weeds, irrespective of the study year, one can see that the tillage system (plough or ploughless tillage) did not affect the value of this parameter. The relations between the values for air-dry weight of weeds were similar to those relating to the above-mentioned trait ( Table 3). The weeds produced a significantly lower weight in 2008 than in the other years. Relative to the year 2007, it was lower by 67.4%, whereas compared to 2009 by more than 53%. The tillage system also modified the trait under study. The weight produced by weeds in the ploughless tillage treatments was more than 31% higher than that in the ploughed plots. Air-dry weight of weeds was also impacted by the interaction of the study years and tillage system. In the ploughless tillage treatments, weeds produced the lowest weight in 2008 (30 g x m -2 ), and the highest one in 2007 (92.2 g x m -2 ).
The tillage systems under evaluation also affected weed species composition. In 2007 the plough tillage treatments were colonized by 30 species, including 27 annual species and 3 perennial ones (Table 4). Among the annual species, the following were found: Avena fatua L., Consolida regalis Gray, Stellaria media (L.) Vill., Chenopodium album L., Galeopsis tetrahit L., and Galium aparine L. Perennial weeds were represented by Cirsium arvense (L.) Scop., Convolvulus arvensis L., and Elymus repens (L.) P.B. In 2008 the presence of 26 species was found -24 annual species and 2 perennial ones. Among the annual species, the following had the highest numbers: Stellaria media L., Chenopodium album L., Avena fatua L., Galium aparine L., Papaver rhoeas L., and Galinsoga parviflora Cav., whereas in the group of perennials, these were Cirsium arvense (L.) Scop. and Convolvulus arvensis L. In 2009 the wheat crop was colonized by 19 weed species -18 annual species and 1 perennial species. Among the short-lived species, the following were predominant in quantitative terms: Avena fatua L., Amaranthus retroflexus L., Papaver rhoeas L., Galinsoga parviflora Cav., Galium aparine L., and Melandrium album (Mill.) Garcke, while in the group of perennials it was Cirsium arvense (L.) Scop.
In analysing the spatial distribution of weeds in the wheat crop, it was found that species belonging to the middle layer made up a large majority, 40% in total, weed species in the upper and lower layers accounted for 22.9% in each layer, whereas weeds in the ground layer constituted 14.2% (Table 6). Differences in weed species composition were found with respect to the tillage systems under comparison, in particular in the middle and lower layers. The following weed species were not found in the plough tillage treatments: Atriplex patula L., Raphanus raphanistrum L., Vicia villosa Roth., Erodium cicutarium (L.) L'Herit, and Galinsoga parviflora Cav. It can be presumed that diaspores of these weeds were located in the deeper soil layers (where they got together with animal manure), and they were moved to the soil surface during ploughing.

DISCUSSION
The literature on weed infestation of cereal plants is very wide and clearly shows significant relationships between crop weed infestation, soil diaspore bank, agricultural practices used, and habitat conditions (F e l ed y n -S z e w c z y k and D u  (2007), carried out under the same soil and habitat conditions, can complement the present study. It shows a great similarity between the soil seed bank and weed infestation of the crop. In the above cited study, the following weed species occurred in the greatest number: Chenopodium album L., Amaranthus retroflexus L., Stellaria media (L.) Vill., Galium aparine L., Viola arvensis Murr., and Avena fatua L.
It can be concluded on the basis of the present study that the tillage system (plough or ploughless tillage) slightly differentiated the number and species composition of weeds, but it significantly affected their air-dry weight. Weather conditions influenced the weed infestation measures to a much greater degree. High rainfall levels had an effect on the increase in the number and air-dry weight of weeds in both tillage systems, as compared to the seasons with lower rainfall levels. Moist soil and appropriately high temperature promote the emergence of weeds, hence their presence is then much higher than in the years with lower rainfall.
The studies of D z i e n i a and D o j s s (1999) as well as of W r z e s i ń s k a et al. (2003) show that the variation in weed infestation between the plough and ploughless tillage systems is a result of different growth conditions that are created by both tillage systems. Under the conditions of ploughless tillage, fruits and seeds of weeds, freshly shed every year, fall onto the soil surface, where they germinate and emerge under favourable conditions. In plough tillage, in turn, during tillage procedures they are moved from the field surface into the deeper soil layers and, at the same time, from the deeper layers onto the soil surface. In the present study, species of the upper layer made up a large group (22.9%), that is, those which mature most frequently before the harvest of wheat and which thereby infest the soil, as well as weeds of the lower and ground layers (37.1%) which mature and shed seeds in the stubble field, also increasing the soil diaspore bank. However, weeds of the middle layer made up the largest group (40%); most of them mature at the same time as spring wheat and they infest primarily seed material as well as the soil.