Dry matter, nitrogen and phosphorus accumulation, partitioning and remobilization as affected by N and P fertilization and source–sink relations

Durum wheat (Triticum turgidum subsp. durum L.) is being increasingly grown in many areas of the world, but there is a lack of information about the physiological processes limiting grain yield. In this study, different rates of N and P fertilization were applied and the source:sink ratio was manipulated to examine the factor(s) limiting grain filling under rainfed conditions. Plants exposed to four fertilization treatments (control, 80 kg N ha−1 (N), 50 kg P ha−1 (P) and 80 kg N ha−1 and 50 kg P ha−1 (N–P)) and were artificially modified to obtain a range of different source:sink ratios. The treatments were (I) control; (II) half of the spike was removed; (III) all the spike was removed. The cultivar Cosmodur was used, which is widely grown in Greece and other Mediterranean countries and is quite productive especially under rainfed conditions. The distribution of dry matter, N and P among grains, stems and leaves was analyzed at anthesis and harvesting. Dry matter accumulation and partitioning into different plant parts was different between the fertilization treatments and the control. At anthesis, leaf + culm dry matter was higher than the chaff dry matter. Total aboveground biomass increased after anthesis in both years and at all fertilization treatments. N fertilization affected N concentration at the whole plant level at anthesis and at maturity. There was an average increase of 20% in N concentration with N application at anthesis in both years relative to the control. N content was affected by the fertilization treatments and it was increased by 33% over the 2 years of the study compared with the control. In addition, P fertilization affected P concentration both at anthesis and maturity in every plant organ, and there was also a significant effect of the change of P concentration at the two different growth stages. P accumulation was also affected by the fertilization regime and by the spike halving treatment. Dry matter translocation was an average of 22% higher at the fertilized treatments compared with the control, which indicates that fertilization led plants to translocate higher amount of dry matter. N and P translocation were affected by the fertilization treatment and in some treatments by the sink reduction. The spike reduction treatment increased the pre-anthesis contribution to seed indicating that the N and P remobilization from vegetative tissues were very important for grain development. The present study indicates that N and P fertilization and sink size can affect dry matter, N, and P accumulation, partitioning, and retranslocation of durum wheat which can affect seed yield.