Integration of Reactive Sensor and Maize-N Model Approaches for Nitrogen Rate Fertigation in Corn.

Applying nitrogen (N) fertilizer during in-season, after the crop is established, and rapid crop uptake is occurring, will achieve good synchrony between N supply in the soil and crop N demand, thus increasing N use efficiency (NUE), maintaining yield and profit, and minimizing N losses. Crop reflectance sensor and maize N-model have been used as approaches to determine variable N rate requirements. The objectives of this research were (i) to evaluate reactive fertigation approaches using sensor and a maize N-model to determine in-season N application rate, (ii) to compare reactive fertigation approaches to best management practice (BMP_S) including University of Nebraska (UNL) algorithm and Holland-Schepers algorithm. The experiment was conducted at the South Central Agricultural Laboratory, near Clay Center, NE during 2016 and 2017. The experiment design was a randomized complete block design with four blocks and eight treatments including check, high N reference, and six different N rate based approaches. The soil plant analysis development(SPAD) chlorophyll meter was used to obtain chlorophyll index (CI) from all treatments in order to calculate sufficiency index (SI) to determine in-season N application rate based fertigation starting from V6 through R6 crop stage. The preliminary results showed that the sensor approach determined less in-season N application rate in 2016 while the sensor, model and combination of sensor approaches determined similar in-season N application rate in 2017. In 2016, the sensor approach had signifyingly higher NUE as partial factor productivity (PFP) than other approaches. However, the yields were not significantly different among approaches except check in 2016 while the yields of 2017 are not shown yet. The results indicated that either sensor or model or combination of both approaches are promising tools and have a great value in determining N rate application via fertigation, increasing NUE, maintaining yield and profit, and minimizing N losses.