Daran R. Rudnick

Economic Return versus Crop Water Productivity of Maize for Various Nitrogen Rates under Full Irrigation, Limited Irrigation, and Rainfed Settings in South Central Nebraska

AbstractField research was conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory (SCAL) located near Clay Center, NE, in the growing seasons of 2011 to 2014. A partial economic analysis was conducted for maize (Zea mays L.) at nitrogen (N) fertilizer treatments of 0, 84, 140, 196, and 252  kg ha−1 under full irrigation (FIT), limited irrigation (75% FIT), and rainfed settings for all growing seasons and then compared to crop water productivity (CWP) measured as crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE). Nitrogen fertilizer increased CWUE and IWUE in all growing seasons. The CWUE values ranged from 0.90 to 2.81  kg m−3 and the IWUE values ranged from −1.01 to 3.24  kg m−3. Operational costs and net income varied among treatments and across years. Irrigation and N fertilizer rate had an interacting effect (P0.05<0.05) on both gross and net income in 2011, 2012, and 2013. Net income was maximized under rainfed settings with a N fertilizer rate...

Impact of Nitrogen Fertilizer on Maize Evapotranspiration Crop Coefficients under Fully Irrigated, Limited Irrigation, and Rainfed Settings

AbstractOne of the common methods for estimating actual evapotranspiration (ETa) is the two-step approach, which relates crop-specific crop coefficients (Kc) to a reference surface ET, typically alfalfa or grass (ETr and ETo, respectively). Minimal, if any, study has reported Kc values for water, nutrient, and both water and nutrient deficiencies. In this study, alfalfa (Kcr) and grass (Kco) reference maize (Zea mays L.) Kc values were developed as a function of growing degree days (GDDs) for 0, 84, 140, 196, and 252  kg ha−1 nitrogen (N) treatments under fully irrigated (FIT), limited irrigation (75% FIT), and rainfed conditions at the University of Nebraska-Lincoln South Central Agricultural Laboratory (SCAL) near Clay Center, Nebraska, for the 2011 and 2012 growing seasons. The research also investigated a stress factor (Kstress) to assess the reduction in crop water use as compared with a nonlimiting water and N treatment (reference). In 2011, maximum Kcr values ranged from 0.95 to 1.27 and occurred b...

Evaluation of Valiantzas’ Simplified Forms of the FAO-56 Penman-Monteith Reference Evapotranspiration Model in a Humid Climate

AbstractThe unavailability of some meteorological variables, especially solar radiation and wind speed, is the main constraint for reference evapotranspiration (ETo) estimation using the standard U...

Crop canopy sensor orientation for late season nitrogen determination in corn

ABSTRACT Increasing nitrogen use efficiency (NUE) in irrigated corn production is of great importance to overall agricultural sustainability. Studies have shown that crop canopy sensors can aid in this pursuit as they allow for the determination of nitrogen (N) requirements in split applications later in the growing season. Fertigation can also increase NUE as many split applications can be conducted. If crop canopy sensors could be used to direct N fertigation rates, overall NUE may be increased even further. However, in some cases, N differences may need to be determined later in the growing season after corn has tasseled, which can cause issues with crop canopy sensor readings. Therefore, a study was initiated to evaluate the potential of a crop canopy sensor to differentiate between N levels at two corn (Zea mays) growth stages (R1 and R3) after the corn had tasseled. The sensor was placed in three orientations to evaluate which orientation best determined the corn N status across two sensor-calculated indices while avoiding taking measurements involving the corn tassel. These orientations were (1) nadir, between corn rows (above canopy), (2) 45° off nadir within the corn canopy (below corn tassel), and (3) 90° off nadir within the corn canopy (below corn tassel). The results of this study show that N differences in late season corn can be determined by utilizing crop canopy sensors in an inter-row orientation. Results also show that the red edge normalized difference vegetation index (ReNDVI) index is superior to the normalized difference vegetation index (NDVI) index for late season N determinations in corn. These results suggest that crop canopy sensors could be an effective tool for determining N requirements of corn late in the growing season.

Variable rate irrigation and nitrogen fertilization of maize across landscape positions

Interactions of water and nitrogen (N) supply for crop production can be quite complex across field landscapes. The availability of variable rate fertilization systems, and now variable rate irrigation systems, gives crop producers the opportunity to adjust inputs of water and N according to variation in soil properties. A study conducted across Nebraska, USA, evaluated interactions of water and N supply with landscape features for irrigated maize in 2011 and 2012. Crop yield response to treatments varied with year, as 2012 experienced severe drought conditions. There was evidence from one site/year that irrigation water use efficiency and agronomic efficiency were correlated, with lower productivity areas of fields requiring different levels of water and N than more productive areas.