The current paper presents the results of experiments carried out at the Lithuanian Institute of Agriculture's Vezaiciai Branch during the period 2005-2009 on a Dystric Albeluvisol (ABd). We explored the effects of farmyard manure, alternative organic and lime fertilisers on soil agrochemical indicators and their relationship with weed incidence in a crop rotation (winter wheat -> lupine-oats mixture -> winter oilseed rape -> spring barley undersown with perennial grasses). Unlimed and farmyard manure - unfertilised soil was very acid, with a pH(KCl) of 4.0-4.3, hydrolytic acidity of 56.32-68.11 mequiv kg(-1) and mobile Al of 77.8-143.7 mg kg(-1). In unlimed soil applied with 40 and 60 t ha(-1) rates of farmyard manure hydrolytic acidity declined to 56.78-40.52 mequiv kg(-1), the content of mobile Al dramatically declined to 39.3-8.5 mg kg(-1), pH(KCl) increased to 4.3-4.6. Unlimed and farmyard manure-unfertilised soil contained 678-777.3 mg kg(-1) of exchangeable Ca and 157.7-163.3 mg kg(-1) of exchangeable Mg. In the soil fertilised with farmyard manure the content of exchangeable Ca increased by 1.4-2.8 times and that of exchangeable Mg by 1.0-1.5 times. In limed soil, the acidity was most markedly reduced by lime fertilisers, only traces (1.0-0.9 mg kg(-1)) of mobile Al were identified, a significant reduction in hydrolytic acidity occurred and pH(KCl) increased. Through the application of all organic fertilisers hydrolytic acidity declined by 17-18%, pH(KCl) value increased by 6-7%, compared with the limed soil. The highest increase (1.3-1.5 times) in exchangeable Ca content resulted from lime fertilisers, while exchangeable Mg content increased by up to 1.5 times. In limed and organically fertilised soil the highest contents of exchangeable Ca and Mg (2917.3-1949.0 mg kg(-1) and 322.7-243.0 mg kg(-1)) were recorded in the treatments applied with 60 t ha(-1) of farmyard manure. Alternative organic fertilisers were not more effective than farmyard manure in reducing soil acidity. The effects of the agricultural practices applied on the crop weed incidence manifested themselves in all experimental years. In the first year of organic fertiliser effect (in the winter wheat crop), strong correlations were established between soil agrochemical indicators and weed number and mass. In the second year of effect, due to the adverse weather conditions and poorer weed suppression capacity of lupine, the relationship between the number of weeds, their mass and individual agrochemical indicators was insignificant, except for that between weed mass and mobile Al content. Strong correlations were established in the third and fourth years of effect for winter oilseed rape and barley crops, respectively.
