Maarika Alaru

Do green manures as winter cover crops impact the weediness and crop yield in an organic crop rotation

Abstract The effects of different winter cover crops and their combination with composted cattle manure on weeds and crop yields were investigated within a five-field crop rotation (barley undersown with red clover, red clover, winter wheat, pea, potato) in three organic cropping systems. The control system (Org 0) followed the rotation. In organic systems Org I and Org II the winter cover crops were used as follows: ryegrass (Lolium perenne L. in 2011/2012) and a mixture of winter oilseed-rape (Brassica napus ssp. oleifera var. biennis) and winter rye (Secale cereale L.) in 2012/2013 before pea; winter oilseed rape before potato and winter rye before barley. In Org II system composted cattle manure was also applied. In comparison with the control system, the winter cover crops, depending on plant species used, reduced the biomass and density of the weeds. In both years winter rye was a better suppressor of weeds than the other winter cover crops. Cover crops increased the yield of potato in rotation crops. When used together with composted cattle manure the cover crops caused significant yield increase in cereals.

Barley undersown with red clover in organic and conventional systems: nitrogen aftereffect on legume growth Miežiai su raudonųjų dobilų įsėliu ekologinės ir tradicinės žemdirbystės sistemose: azoto įtaka pupinių augalų augimui

Nitrogen (N) deficiency is a major problem in organic and low-input farming systems. Growing spring cereals with undersown legumes has a positive effect on soil fertility, enriching it with nitrogen, through symbiosis of legumes with nodule bacteria. Two hypotheses were tested: 1) undersowing of red clover increases the protein content of barley grains and 2) mineral N has negative aftereffect on growth of legume plants. The aim of this study was to investigate the effect of organic (cattle manure, off-season cover crop) and mineral N in organic and conventional farming systems on (i) barley (Hordeum vulgare L.) grain yield and quality, (ii) biomass yield formation of undersown red clover (Trifolium pratense L.) and (iii) the aftereffect of mineral and organic N fertilisers on the red clover crop biomass yield in the following year. The experiment was established in 2008 at the Estonian University of Life Sciences (58°22ʹ N, 26°40ʹ E) on the soil described as Stagnic Albic Luvisol (LV ab-st) (WRB, 2014) with sandy loam surface texture, 1.38% C, 0.13% N, 133 mg kg-1 P, 210 mg kg-1 K and pHKCl 6.0. The crops were treated using different farming systems: three organic (Org0, OrgI and OrgII) and four conventional (N0, N40, N80 and N120); nitrogen sources during crop cycle period: N0 and Org0 = symbiotically fixed atmospheric N2, N40 = N2 + mineral N 40 kg ha-1 N, N80 = N2 + mineral N 80 kg ha-1 N, N120 = N2 + mineral N 120 kg ha-1 N, OrgI = N2 + N taken up by cover crops (NCC) and OrgII = N2 + NCC + N applied with manure (Nm). Our study revealed that grain yield of barley was strongly affected by undersown red clover; because of competition for nutrients in cereallegume mixture the grain yield of barley in organic system was 11‒61% lower than that in conventional system. The seed rate of undersown red clover (2.84 million viable seed per ha) was too high. The content of proteiin depended on the availability of mineralised nitrogen. The mean protein content of barley grains over the trial years and treatments was 99 ± 1.6 g kg-1 in the conventional system, which was 17% higher than that in the organic system. Undersowing of red clover had no significantly positive effect on the grain yield and protein content of barley. Mineral N fertiliser had no negative aftereffect on growth of the red clover crop the following year. Mean above ground biomass yield over the trial years for the red clover crop 2nd cut was 17% higher in the conventional system than in the organic system.