Kaun- ja teraviljade segukülvide kasvatamise teoreetilisi ja praktilisi aspekte
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In Estonia cereals and legumes are grown together for the purpose of gaining grain yield. With mixed crops, it is tried to imitate natural compositions, whose productivity is often higher than that of one single species. As components of mixed crops are differently located in abovesoil and insoil plant organs and have different biological needs, mixed crops make better use of the possibilities offered by their growth environment than single species sown. This research involved vetch and pea as the legume components of mixed crops. Both the papilionaceous plants belong to valuable feedplants rich in protein. They are productive, can be used as feed for a long period and have a valuable chemical content. Vetch and pea are grown together with other grasses for green fodder, green fertiliser, seed, silage, and hay. In our conditions, support cultures suitable for the legumes selected are wheat, oats, and barley. The hypothesis of this research was that the synergic effect of legume–cereal mixed crops may considerably depend on both natural factors (rainfall) and conditions created by humans (different support cultures, sowing density, the ratio in the seed mix, fertilisation with nitrogen). The research had the following main objectives: To establish how competition between legumes and cereals affects the • yield potential of different species. To find the optimum sowing rate and the right ratio of components • for mixed crops, as well as to determine the most suitable support crop for legumes when growing them for seed and fodder. To estimate the value of legume–cereal mixed crops for the seed yield, • protein yield and the protein content of the yield. To find out the extent of the effect of nitrogen fertiliser in vetch–wheat • mixed crops at different ratios, compared with pure cereal crops. To assess the effect of meteorological conditions on yields of mixed • crops. Thus the hypothes that the synergic effect of legume–cereal mixed crops may considerably depend on both natural factors (rainfall) and conditions created by humans (different support cultures, sowing density, the ratio in the seed mix, fertilisation with nitrogen) was confirmed. The synergic effect of growing vetch–wheat mixed stands after cereals appears as the yield level of single crops below 3000 kg ha–1. The results of experiments carried out with mixed crops revealed that, in legume–cereal mixed crops, there was strong interspecies competition whereas the more aggressive party were the legumes. Of cereals, oats cv. Jaak proved somewhat more competitive than wheat cv. Tjalve. When growing vetch and pea varieties for seed together with a support culture, wheat should be the cereal used. In mixed crops, the seed yield of cereals, 1000–seed weight and protein yield from a surface unit were decreased when the sowing rate of legumes was increased. From the position of the yield, vetch–cereal mixed crops, when they followed cereals, had, as the average of 2000–2002, no considerable advantage over pure wheat crops, which was caused by the relatively high yield of wheat in the pure crops and the draught in 2002. Larger yields (2882–3814 kg ha–1) were gained as the average of 2003 and 2004 at a sowing rate of 40–50 germinating vetch cv. Carolina seeds m–2. It appeared that the vetch–wheat mixed crops lost their yield advantage, when they followed cereals, in case the yield level of pure wheat crops exceeded 3000 kg ha–1. In conditions when the yield level of pure wheat crops was between 1500–3000 kg ha–1, vetch–wheat mixed crops ensured a yield of ca 3000 kg ha–1 at 300±50mm precipitation in the growth period. As the average of 2000–2002, the maximum yield was gained from pea–cereals (wheat, oats) mixed crops (2776–3380 kg ha–1) at a sowing rate of 40–60 germinating pea cv. Kirke seeds m–2. As the average of the two next years (2003–2004) of much precipitation, pea–cereals (wheat, oats) mixed crops produced the maximum yield (2860–3500 kg ha–1) at a sowing rate of 70–80 germinating pea seeds m–2. The lowest total yield was in combination pea+barley cv. Elo. At the lowest legumes seeds density (20 germinating seeds per 1m–2) the yield of pea was two times lower than the yield of vetch at the same seed density. Legume–cereal mixed crops have an advantage over pure cereal crops with their protein yield. Generalisation of a longer period shows that, with normal water supply, vetch–wheat mixed crops following a cereal ensure 600–700 kg protein yield per hectare (the protein yields of pure wheat crops in the same conditions were between 175–480 kg ha1). The effectiveness of nitrogen fertiliser in fertilisation of pure crops depended considerably on the meteorological conditions in the growth period. As the average of 2000–2001, the average effectiveness of N fertiliser (N68) in pure crops was 9.4 kg seeds per 1 kg of nitrogen. In fertilisation with nitrogen (N34, N 68), a maximum mixed crop yield was gained in case 12 germinating seeds of vetch and 438 germinating seeds of wheat were added to the seed mix. With fertilisation of vetch–wheat mixed crops, the effectiveness of nitrogen fertiliser was considerably lesser than in pure wheat crops as the fertilisation affected the yields of different components differently – wheat positively and vetch negatively. As, with protein yields, fertilisation also affected wheat positively and vetch negatively, the effect of the fertiliser on the protein yield of mixed crops was relatively modest and not plausible at a smaller N fertiliser norm. With respect to protein yields, vetch–wheat mixed crops can be grown without N fertiliser. Legume–cereal mixed crops are ideally suited in conditions of ecological agriculture as they ensure a considerably good yield also in cases no N fertiliser is used. In conditions of traditional farming, legume–cereal mixed crops help save N fertilisers.