Effect of rate and method of phosphate placement on productivity of durum wheat in a Mediterranean climate

Abstract

The authors demonstrated in part I that phosphate banded with the seeds of durum wheat (Triticum vulgare), L., cv. Sham 1) was generally superior to broadcasting in improving P uptake, especially at early growth. These results were confirmed for three consecutive seasons at three experimental sites with calcareous soils in Northern Syria (mean annual rainfall 281–471 mm).

Two mechanisms have been postulated by various authors to explain the advantageous effect of banding on P fertilizer use efficiency: i) banding reduces soil to fertilizer contact resulting in less immobilization of P by fixation in the calcareous soils and ii) banding increases the root to P fertilizer contact and concentration, resulting in greater P uptake.

The present work was designed to test these two hypotheses by measuring within the surface 20 cm of soil, i) the effect of method (banding vs. broadcasting) of P application (0, 17.5 and 52.5 kg P ha⁻¹ as triple superphosphate) on the change of NaHCO₃-extractable P with time and ii) the length and distribution of roots at tillering in relation to the distribution of available P in the soil.

It was found that: i) The reduction in P availability with time was independent of the method of P placement and the residual NaHCO₃-P one year after its application was practically the same (for the same rate of P, whether banded or broadcast; and ii) the growth of roots was increased in the volumes of soil containing the P fertilizer, particularly where P was banded.

It was concluded that, for wheat grown in calcareous soils in a Mediterranean climate, the greater uptake of P by crops where the fertilizer was banded was due to an increased probability of contact between roots and P fertilizer granules.