Estonia is situated in Northeastern Europe, being the smallest and northernmost of three Baltic States. The aims of wheat breeding are high and stable yielding varieties with suitable growing time, good kernel quality, milling and baking quality, lodging and disease resistance. Organic farming is one of the fastest growing segments of agriculture and organic food is becoming more popular all over the world. In Estonia, the organic land area has expanded 2.5 times over the last ten years, reaching 200 th ha in 2017 thus covering ca 20% of the total agricultural area. Organic rotations need more nitrogen-fixing crops for improving soil fertility and achieving high yields and quality of subsequent spring (SW) and winter wheat (WW).

In 2011-2012 the value of the following perennial legumes as pre-crops were tested: red clover, alsike clover, Washington lupine, white sweet clover Alexandria clover and crimson clover. Timothy was used as a control. Two SW and WW varieties were followed on 5m2 plots in three replications. Influence of legumes to yield, grain weight, protein content and loaf volume of wheat was measured. All statistical analyses were performed using the Agrobase 4 package. Determination indexes were expressed for genotype, pre-crop and genotype by pre-crop interaction.

Average dry matter yield and amounts of C and N in the perennial and biennial leguminous species were considerably higher than that of the annual clovers. Different legume species can fit in different niches in diverse crop rotations. SW and WW produced significantly higher grain yields in the subsequent year. SW and WW were influenced differently by perennial, biennial and annual legume species. The yields of SW increased the most after red and alsike clover followed by lupine. In contrast, the best pre-crops for WW were sweet clover and annual clover species. Yield gain compared to control was high (157-255% for SW and 143-325% for WW). All the green manure pre-crops increased significantly TKW and loaf volume of the both wheat types. Spring wheat was more sensitive to the shortage of nitrogen in the soil for the production of protein than winter wheat. Protein content (PC) ranged from 8.7 to 13.1% for SW and from 10.6 to 11.8% for WW. According to determination index the influence of pre-crop to PC was quite similar for both wheat types (6567%). Influence of pre-crop to yield was 78% for SW and 84% for WW.