The evolution of soil fertility under long-term experiments in the Moldavian Plateau

anglais. The paper presented the results of investigations concerning the influence of long-term fertilization (43 years) on some chemical characteristics of soil from the Moldavian Plateau, of wheat-maize rotation. The studies were performed on a typical cambic chernozem soil, prevailing in the Moldavian Plateau, and followed the dosing of fertilizers which ensures an efficient production increases and determines maintain or increase soil organic carbon content. Soil that has been placed experiences-clay loam, neutral to slightly acid reaction and a medium nutrient supply. On lands from the Moldavian Plateau, maintaining a good supply in mobile phosphorus for field crops (37-72 mg/kg) was done in case of the annual application of a rate of N100P100, and a very good supply in mobile phosphorus (69-78) and mobile potassium (over 200 mg/kg) was found at a rate of N100P100+60 t/ha manure. In wheat-maize rotation, applying a rate of N100P100, for 43 years, has determined the pH decrease until the limit of moderately acid interval (5.1-5.8) and was maintained within the weakly acid interval (5.9-6.8) in case of the annual application of a rate of N50P50 + 60 t/ha manure. Soil organic carbon content, in wheat-maize rotation, decreased after 43 years of experiences from 19.8 to 16.3 g/kg in unfertilized variant and until 18.1 g/kg in case of the annual application of a rate of N100P100. In wheat - maize rotation, the significant increase in organic carbon content from soil has been registered at higher than N50P50 + 40 t/ha manure and at N100P100 + 60 t/ha manure. The determinations of mean annual amounts of nitrogen exported from soil by wheat (grains + straw) have shown that in wheat crop, its values varied according to fertilizers system, between 71.5 and 128.4 kg/ha. In maize crop, of the mean annual amounts of nitrogen exported from soil varied according to applied fertilizers, between 64.6 and 178.9 kg/ha.

roumain; moldave. Lucrarea prezinta rezultatele cercetarilor privind influenta fertilizarii de lunga durata (43 ani) asupra unor insusiri chimice ale cernoziomului cambic din Podisul Moldovei, in rotatia grau-porumb. Studiile au fost efectuate pe un sol cernoziom cambic tipic, care predomina in Podisul Moldovei, si au urmarit stabilirea dozelor de ingrasaminte care asigura obtinerea unor sporuri eficiente de productie si care determina mentinerea sau cresterea continutului de carbon organic din sol. Solul pe care au fost amplasate experientele are o textura luto-argiloasa, o reactie neutra spre slab acida si o aprovizionare mijlocie in elemente nutritive. Pe terenurile in panta din Campia Moldovei, mentinerea unei aprovizionari bune cu fosfor mobil pentru culturile de camp (37-72 mg/kg) s-a realizat in cazul aplicarii anuale a dozei de N100P100, iar realizarea unei asigurari foarte bune cu fosfor mobil (69-78 mg/kg) si potasiu mobil (peste 200 mg/kg) la doza de N100P100+60 t/ha gunoi. In rotatia grau-porumb, aplicarea unei doze de N100P100, timp de 43 de ani, a determinat scaderea pH-ului pana la limita intervalului acid moderat (5.1-5.8) si s-a mentinut in intervalul slab acid (5.9-6.8), in cazul aplicarii anuale a dozei N50P50 + 60 t/ha gunoi de grajd. Continutul de carbon organic din sol, in rotatia grau-porumb, a scazut, dupa 43 de ani de experienta, de la 19.8 la 16.3 g/kg la varianta nefertilizata si pana la 18.1 g/kg in cazul aplicarii dozei de N100P100. In rotatia grau-porumb, cresterea semnificativa a continutului de carbon organic din sol a fost inregistrata la doze mai mari decat N50P50 + 40 t/ha gunoi de grajd si la N100P100 + 60 t/ha gunoi de grajd. Determinarile privind cantitatile medii anuale de azot exportate din sol la grau (boabe + paie) arata ca valorile au variat, in functie de sistemul de ingrasaminte, intre 71.5 si 128.4 kg/ha. La cultura de porumb, cantitatile medii anuale de azot exportate din sol au variat, in functie de ingrasamintele aplicate, intre 64.6 si 178.9 kg/ha.