Experiments with increased nitrogen (0-320) and phosphorus (0-160) rates performed during last 40 years in the South of Romania, on cambic chernozem of Fundulea, under dryland and irrigation conditions were analyzed to determine the evolution of soil features, wheat and maize yield and fertilizer necessary and efficiency.
The main soil agro-chemical features registered the pH decreasing from the initial value of 6.42 till 5.68, on unfertilized soil, till 5.21 at fertilization with N150 and 5.51 at fertilization with N150P160. The mobile phosphorus content has diminished from 64 to 14 ppm PAL, on unfertilized soil and has increased by phosphorus fertilization to 64 ppm PAL at 80 kg P2O5/ha rate and to 127 ppm PAL at 160 kg P2O5/ha rate. The potassium content has decreased during this period from 240 to 160 ppm KAI, on unfertilized soil and to 135 ppm KAI on NP fertilization at optimum rates. The humus content has increased obviously on unfertilized soil (from 2.9 till 3.3%) and from 3.2 till 3.5% on fertilized soil.
The yielding capacity of unfertilized soil expressed by wheat yield decreased with 50% approximately and with 20-25% in maize, especially under dryland. By NP optimum fertilization, the yields remain relatively constant with an increasing during 1970-1985, under more favorable conditions.
The nitrogen fertilizer necessary increased during experimentation, depending on the climatic conditions of the year, till 115 kg N/ha in non-irrigated wheat and 140 kg N/ha in irrigated wheat. In maize, the optimum nitrogen rates remain relatively constant under dryland (100-120 kg N/ha) and ranged between 150-180 kg in irrigated maize, depending on the level of yields. The phosphorus fertilizer necessary were between 30-80 kg P2O5/ha in wheat, with increasing tendency and had low values in maize (0-25 kg P2O5/ha) under both dryland and irrigation, with possibility of using the residual effect of phosphorus from wheat by maize crop.
The efficiency of fertilizer utilization (grain at 1 kg a.i.) has increased during the first 20 years of application, in optimum rates, till 20 kg wheat/NP under both crop conditions (dryland-irrigation) and till 12 kg maize/ NP under dryland and 20 kg maize/ NP under irrigation, maintaining constant during 40 years.
The obtained data suggest the possibility to improve the fertilization strategy depending on the response of these two crops and related to environment conditions, as well as improvements of experimental model.
