An important problem refers to soil weeds seed bank with special reference to brown luvic soils and relationship between vegetal remains(roots + stub) and nutrition regime – crop rotation plant. A great number of seeds can be found in first 20 centimeters of soil (plowinglayer). This fact causes a high weeds density, which has a negative effect on the cultivated plants leading to partial or total crop loss.

The paper is based on the researches carried out during 2003-2008 in a long term trial placed in 1990 on the preluvosoil from Oradea. Climate indicator “de Martonne aridity index” (IdM) was used for quantification the correlation between climate and wheat yield in unirrigated and irrigated conditions and new class called “arid” was purposed for climate index characterization. Maintaining the soil water reserve on 0-50 cm depth between easily available water content and field capacity using the irrigation determined the increase of the IdM values for period IV – VI with 79% in 2003, 73% in 2004, 36% in 2005,16% in 2006, 162% in 2007 and with 131% in 2008; using the irrigation and the improvement of the microclimate conditions determined to obtain the yield gains, very significant every year and every crop rotation studied; both in unirrigated conditions and in irrigated conditions, the smallest yields wheat were obtained in monocrop and the biggest in the wheat – maize – soybean crop rotation; in the all three crop rotation, the direct links statistically assured were registered between the values of the De Martonne aridity index and yields in unirrigated and irrigated wheat. These correlations sustain the need of the irrigation in wheat from Crisurilor Plain; correlation between De Martonne aridity index is stronger (R2 = 0.7361xx) in the wheat – maize – soybean crop rotation in comparison with wheat – maize crop rotation (R2 = 0.6215x) and with wheat monocrop (R2 = 0.6105x). As consequence, crop rotation of wheat-maize-soybean is recomanded because the climate and microclimate conditions are better use.

The paper based on the researches carried out during 2006-2008 in the long term trial placed in 1990 on the preluvosoil from Oradea. Three kind of crop rotation (wheat – monocrop; wheat – maize; wheat – maize – soybean) were studied in unirrigated and irrigated conditions. The smallest content of the protein from wheat grains were registered in the wheat monocrop both nonirrigated and irrigated variant. In the wheat-maize and wheat-maize-soybean crop rotation the values registered were significant statistically bigger than in wheat monocrop. Irrigation determined the decrease of the protein content.