Objectives :

1. SECRETARIA DE AGRICULTURA, GANADERIA, PESCA Y ALIMENTACION INSTITUTO NACIONAL DE TECNOLOGIA AGROPECUARIA Use of sensor based nitrogen rates to improve maize nitrogen use efficiency in the Northern Argentinean Pampas. Ricardo Melchiori1, Octavio Caviglia1, Agustín Bianchini2, Nelson Faccendini3, and William Raun4 1INTA EEA Paraná, Argentina 2AAPRESID, 3FCA-Univ. Nac. de ER, 4Oklahoma State University. rmelchiori@parana.inta.gov.ar Objectives: • To evaluate delayed nitrogen application effects on maize grain yield and nitrogen use efficiency. • To determine nitrogen status, dry matter accumulation, and crop coverage on sensor capabilities to detect N deficiencies. Materials and methods Results Four experiments (E) were conducted during the 2004-05 (E1 and E2) and the 2005-06 (E3 and E4) growing seasons in Paraná, Argentina. (31.5ºS). E1 and E3 were timely sowed and treatments included combinations of N rates at planting (0, 70, 140 y 210 kg N ha-1) and two strategies to late N fertilization: a fixed rate (FR = 70 kg N ha-1) and a variable rate (SBNRC). In both strategies, N was broadcasted as urea at V8, V10, V12 and V14 growth stages. E2 and E4 were late planted and treatments included N rates at planting (0, 50, 100 and 200 kg N ha-1 in E2 and 0, 70, 140 and 210 kg N ha-1 in E4) and a late N application at V12 using a fixed rate (50 kg N ha-1 in E2 and 70 kg N ha-1 in E4) or a variable rate (SBNRC). Periodically, normalized difference vegetative index (NDVI) measurements were taken using a Green Seeker Sensor (NTech Industries, Inc., CA, USA). INSEY (in season estimation of yield) was calculated as a ratio between NDVI and days between planting and sensor measurements. In coincidence with sensor readings, shoot dry matter and N concentration were determined to calculate N uptake. At maturity, grain yield, shoot dry matter and N concentration in grain and total plant were recorded. Nitrogen use efficiency (NUE) of total N applied and LF was calculated as grain yield / N applied. E1 and E2 showed that maize grain yield was similar between strategies and NUE was higher with the SBNRC. Average crop yield was higher (9%) in fixed rate and total N applied was lower (17%) in SBNRC. In spite of a severe drought in the 2005/06 (E3 and E4) season, that significantly reduced crop yield and N response irrespective of N strategy; NUE was higher in the SBNRC. However, despite of promissory results on NUE increases, more studies to improve yield predictions in late planting dates are needed. Figure 2. Total fertilizer applied with fixed rate and variable rate (SBNRC) assistance (E1). Figure 1. Relationship between maize yield with fixed and variable rate (SBNRC) (E1). Conclusions Sensor-based N prescription tools are available to Argentinean farmers, and are showing promissory results to increase NUE. More studies to improve yield predictions in late planting dates are needed. Figure 3.NUE with fixed and variable rate (SBNRC) in late planting maize. (E2) Acknowledgments: This work was possible by the financial support from INTA and PROFERTIL SA