Nitrogen accumulation and partition in two wheat cultivars with N fertilization in no-till and conventional tillage.

Nitrogen dynamics and crop response to N fertilization under conservation tillage (as no-tillage) can be different from those under conventional tillage, modifying N accumulation and partition in the crop, and the efficiency in fertilizer use. The aim of this paper was to study N accumulation and partition and its relationship with grain N content in two wheat (Triticum aestivum L ) cultivars under conventional tillage (LC) and no-tillage (SD) systems with different N availability. Nitrogen fertilization consisted in a) application of 90 kg N.ha-1 at sowing and b) the same rate split in two 45 kg N.ha-1 applications, one at sowing and the other at the end of tillering. Nitrogen accumulation and partition between different plant parts were evaluated at third node and at ripeness stages. Total N in plant at ripeness was 23% greater under LC (128 kg.ha-1) than SD (104 kg.ha-1), which was associated with higher total aerial biomass values. No differences in N partition towards the grain were found among tillage treatments. Nitrogen percentage in the grain was increased only when N was applied in two moments, but was not affected by tillage and did not differ between cultivars. Apparent N recuperation in plant and grain were affected neither by tillage nor by time of N application. However significant differences between cultivars were found. No interaction between tillage, fertilization and cultivars were found for those variables associated to N accumulation and partition in the crop. No differences were observed in cultivar response to tillage and fertilization, which is attributed to similar N accumulation rates. It is concluded that under no-tillage total N accumulation in the crop is lower than in conventional tillage, but it does not affect N partition, which is more associated with N fertilization and cultivars. Nitrogen fertilization, specially in split application, enhances N crop accumulation without a decrease in the eficiency of N partition towards the grain. The lack of a favourable response to N application under no-tillage treatment, suggests the existence of other limitations to crop development, besides N deficit in the soil.

key words: NHI, split fertilization, critic nitrogen value, nitrogen nutrition index (NNI).