Nitrogen indicators, uptake and utilization efficiency in a maize and barley rotation cropped at different levels and sources of N fertilization

A 3-year experiment was carried out in Mediterranean conditions on two maize-barley rotations to determine the effect of different levels and sources of nitrogen (N) fertilizer on the N uptake, efficiency, soil N deficit and crops yield. The potential for N savings by the use of N indicators was also studied. Five strategies of maize N fertilization were compared on plots laid out in a complete randomized design with three blocks: mineral N (200 kg N ha(-1)); organic-mineral N (100 kg N ha(-1) as olive pomace compost plus 100 kg ha(-1) of mineral N); mineral N (100 kg N ha(-1)); organic N (100 kg N ha(-1) as olive pomace compost); unfertilized control. Winter barley was cultivated without fertilization. The use of organic fertilizer, as a partial substitution of mineral N, achieved the same yield of the highest mineral fertilizer treatment in maize (8.8 and 8.9 t ha(-1), respectively) and barley (3.2 and 3.5 t ha(-1)), ensured the highest increases of total organic carbon and the least N mineral soil deficit at the end of the experiment. Furthermore, N utilization efficiency indices did not change between the highest N treatments (mineral and organic-mineral N supply) in both crops, reflecting no difference in N utilization. High level of available N in the soil during the growing seasons strongly affected the total N uptake in both crops and, consequently, yield and N utilization efficiency. In fact, as mean of N treatments, the available N contributed to total N uptake for the 57.4% in the first growing period (maize 2000 and barley 2001) and 45.2% in the second one (maize 2001 and barley 2002). The findings of this research also indicate that the postanthesis N uptake was higher than preanthesis in maize (59.1 and 40.9% of the total N uptake, respectively) but lower in barley (32.8 and 67.2%), although it was correlated with yield in both crops, confirming that the reproductive stage is more important than the vegetative one in Mediterranean conditions. Finally, the results showed that the more reliable N indicator tests of yield for maize were the pre-sowing soil mineral N and the mean of SPAD readings, which presented a linear relationship. In barley, the best N indicator was the mean stem nitrate content, which showed a high,correlation and linear relationship with yield. (c) 2006 Elsevier B.V. All rights reserved.