Fertilizer Nitrogen Recovery in Irrigated Upland Cotton

Abstract

Field studies were carried out for the purpose of evaluating fertilizer nitrogen (N) recovery of upland cotton by use of the difference technique. The treatments under study included : i) check (no fertilizer N applied), ii) standard approach (preplant and sidedress), iii) feedback approach (based upon soil and plant factors), and iv) 2X feedback approach. The studies were carried out at two locations Maricopa (MAC) and Marana (MAR). MAC is a low elevation location with a coarser textured soil compared to the MAR location. 'DPL-20' was the variety used in both locations, except for the early years at MAC where 'DPL-90' was used. The sources of fertilizer N were urea and ammonium sulphate, which were sidedress and split applied. In general, for the MAC location the final N fertilizer rates (NFR) applied were higher than for MAR due to higher yield potentials. The total N uptake increased as the NFR increased. The N use efficiency (NUE) values were reduced as NFR increased. The N fertilizer uptake (NFU) showed a decreasing pattern in the first years, and then an increasing trend; which was coupled with rather high amounts of N taken up in the check plot (soil N mineralized). When the N uptake in the check plot was high, NFU values were low, and vice versa. At MAC the N uptake in the check plot, apparently due to mineralized soil N revealed a slight increasing trend during the first years and then, after the fourth year, a rapid reduction of the mineralized soil N (check plot). A similar pattern was observed for MAR, although the total amount of N taken up was smaller compared to the MAC location.