Maize evapotranspiration, canopy and stomatal resistances, crop water productivity, and economic analysis for various nitrogen fertilizer rates under full irrigation, limited irrigation, and rainfed settings

Abstract

Research was conducted for maize (Zea Mays L.) under various irrigation and nitrogen (N) fertilizer treatments at the University of Nebraska-Lincoln South Central Agricultural Laboratory located near Clay Center, NE in 2011 to 2014. The N fertilizer treatments were 0, 84, 140, 196, and 252 kg ha-1 and the irrigation treatments were full irrigation, limited irrigation (75% of full), and rainfed. The overall objectives of the study were to assess the differences in maize actual evapotranspiration (ET _a), canopy resistance (r_c), stomatal resistance (r_s ), economic return, and crop water productivity as influenced by the imposed treatments as well as improve estimation techniques of the aforementioned by developing local crop coefficients (K_c), scaling up r_s to r_c, and developing a new function, f(SPAD), to account for N stress when modeling r_s.

Maize ET_a ranged from 426 to 550, 411 to 535, 353 to 480, and 445 to 519 mm in 2011, 2012, 2013, and 2014, respectively. In almost all cases ET_a increased with irrigation and, in general, ET_a increased with increasing N fertilizer application. The greatest crop ET _a rates and consequently, the highest K_c values as well as the lowest r_c values occurred during the early reproductive growth stages. The Jarvis-Stewart (J-S) model for estimating r_s was calibrated and evaluated using field measured r_s from a model AP4 dynamic diffusion porometer. The measured r_s values ranged from 37 to 2300 s m^-1 in 2013 and 2014. For individual dates, the SPAD function decreased RMSD in the range of 1% (7/22/14) to 28% (6/17/13) and maintained or slightly improved Willmott's index of agreement in all cases. The SPAD function improved model performance the most under the 0 kg N ha^-1 treatments, which experienced the greatest N stress.

A positive relationship existed between net income and crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE). With consideration to IWUE, CWUE, and partial factor productivity of N, we recommend full irrigation under non-water limiting conditions and limited/deficit irrigation management strategies when water is limited, with N fertilizer rate not exceeding 196 kg ha^-1 to achieve high economic return for the study area.