Kvickrotsstudier: 1. Kvickrotens reaktion på myllningsdjup, kvävemängd och kväveplacering i konkurrens med gröda. 2. Reducerad glyfosatanvändning på trädad åkermark

Sammanfattning: 1. Reaction on burial depth and nitrogen availability and placement in competition with a crop In this trial it was investigated how couch grass (Elymus repens) changes its ability to compete in stands of wheat and barley with different burial depth and different amounts and placement of nitrogen. More knowledge in this area can be valuable in the attempt to decrease the use of herbicides and still keep the weeds under control. The trial was carried out in the summer of 2004 as an outdoor pot experiment. The pots contained 15 litres of soil with a surface of 0,06 m2. Couch grass was planted at two different depths, 2 cm and 6 cm under the soil surface. At the same time tree different stands of cereals were established in the pots. Spring wheat was planted with 12 or 36 kernels in each pot or spring barley with 28 kernels in each pot. The cereals were seeded at a depth of 2 cm. The different stands of cereals and couch grass were grown at two different levels of nitrogen supplay, a high level, corresponding to 150 kg/ha N, and a low level, corresponding to 40 kg/ha N. The nitrogen was supplied in form of calcium nitrate and was either placed 3-5 cm or 7-9 cm under the soil surface. After harvest the plant material was dried, and the biomass measured by weight. Both for couch grass and cereals the biomass produced above ground was measured. For couch grass the biomass of the underground plant parts (horizontal rhizomes and vertical shoot bases) were also measured. The results indicated that couch grass was favoured by a high availability of nitrogen. When the supplied amount of nitrogen increased from about 40 kg/ha to about 150 kg/ha, the biomass production of couch grass increased proportionally as much as it did for barley and more than it did for wheat. This means that the higher level of nitrogen did not favour the cereals in their competition with couch grass. The results also suggest that couch grass was favoured when nitrogen was placed closer to the planted rhizomes. Thus, when couch grass was planted at a depth of 2 cm and nitrogen (150 kg/ha N) 5-7 cm below the planting depth, the biomass production was about 20 % lower than when the nitrogen was placed 1-3 cm below the planting depth. The difference between the two nitrogen placements was smaller at the lower nitrogen level than at the higher. The biomass production of wheat and barley was not measurably affected by the placement of nitrogen. Couch grass planted at the 6-cm depth produced almost the same amount of biomass either the nitrogen was placed 1-3 cm above or 1-3 cm below the planting depth. But the result may have been affected by heavy rainfall during a period shortly after planting. Most nitrogen was added as nitrate which is easily transported downwards in the soil. At the higher nitrogen level couch grass planted at a depth of 6 cm produced 20 % less biomass than couch grass planted at a depth of 2 cm. The difference between the two nitrogen placements was smaller at the lower nitrogen level. The result also indicated that spring wheat, when compared to barley and couch grass, was a stronger competitor at the lower nitrogen availability than at the higher. 2. Reduced use of glyfosat on fallow The purpose of this study was to investigate whether it is possible to decrease the use of glyphosate on fallow and still control couch grass (Elymus repens). The possibility to combat herb weeds was also partly studied. The trials were designed as split plot, with randomised blocks and four replicates. Three trials a year were started during a period of three years, which gives a total of nine trials. Five main strategies (A, B, C, D and E) for treating the fallow were compared. Every strategy was carried out partly on fallow with a catch crop and partly on fallow without a catch crop. The first year, cereals were grown, and half of each plot was under sown with a catch crop. No measurements were carried out the first year. The second year herb weeds and shoots of couch grass were counted at the end of May. In the beginning of June, when the couch grass had reached a length of about 20 cm all plots were mowed, except those treated accordingly to strategy A. One month later, when the couch grass once more had reached a length of 20 cm all plots were mowed, except those treated accordingly to strategy A and B. They were instead sprayed with full and half dose of glyphosat respectively. About one week later plots belonging to strategy E were cultivated with a tine cultivator to a depth of 10-15 cm. At the beginning of August strategy D was mowed for the third time. Plots treated according to strategy A, B, C and D were ploughed at the beginning of August and plots in strategy D were ploughed one month later. After seedbed preparation winter wheat was sown in almost all trials. In the following autumn the yield of winter wheat was measured and after harvest the shoots of couch grass were counted. In strategy C, D and E also the volume of couch grass rhizomes was measured. The results showed that competition from a catch crop reduced the possibility of weeds to increase in number on the fallow. In springtime the second year (the fallow year), there were on average about 47 % less herb weeds and 36 % less shoots of couch grass in plots with a catch crop. In autumn after harvest of winter wheat the volume of rhizomes was smaller, 36 % on average, where a catch crop had been grown and in several trials more than 70 % smaller. The grain yield was on average slightly higher after fallow in combination with a catch crop. Among the strategies investigated the best effect against couch grass was found in plots treated according to strategy A (full dose of glyphosate applied on 1 July and ploughed on 1 August). The couch grass shots decreased on average with 75 % between the two countings (between springtime the second year and after harvest of winter wheat the third year). The second best effect against couch grass was found in strategy E (mowed twice, cultivated to a depth of 10-15 cm on 10 July and ploughed on 1 August). There the number of shots decreased on average with 53 %. In strategy B (mowed once, half dose of glyphosate on 1 July and ploughed on 1 August) the number of couch grass shots decreased on average with 30 %. Strategy C (mowed twice and ploughed on 1 August) and strategy D (mowed three times and ploughed on 1 September), on the other hand, led to an increase in couch grass shots of 11 and 45 %, respectively. The yields of winter wheat were similar in strategy A, B and E, but strategy C and especially D yielded less. On average the smallest volume of rhizomes was found in strategy E and the greatest in strategy D. The volume was only measured in strategy C, D and E. Treatment with glyphosate had a better effect without a catch crop: At the second counting, 51 % more shoots were found in plots with a catch crop. Strategy A was supposed to correspond to a "conventional treatment" of fallow. If this can be considered a correct assumption, the results indicate that it is possible to reduce the use of glyphosate without any negative effects on the following winter wheat crop yield. However more couch grass will remain in the fields compared with a treatment with full dos of glyphosate. This can imply a quicker increase in couch grass density and thereby also a reduction of crop yields the succeeding years.