Optical crop sensor for variable-rate nitrogen fertilization in corn: i - plant nutrition and dry matter production

Jardes Bragagnolo,Junior Kunz,Telmo Jorge Carneiro Amado,Rodrigo Da Silveira Nicoloso,Joerg Jasper,Tiago De Gregori Teixeira

doi:10.1590/s0100-06832013000500018

Abstract

Variable-rate nitrogen fertilization (VRF) based on optical spectrometry sensors of crops is a technological innovation capable of improving the nutrient use efficiency (NUE) and mitigate environmental impacts. However, studies addressing fertilization based on crop sensors are still scarce in Brazilian agriculture. This study aims to evaluate the efficiency of an optical crop sensor to assess the nutritional status of corn and compare VRF with the standard strategy of traditional single-rate N fertilization (TSF) used by farmers. With this purpose, three experiments were conducted at different locations in Southern Brazil, in the growing seasons 2008/09 and 2010/11. The following crop properties were evaluated: above-ground dry matter production, nitrogen (N) content, N uptake, relative chlorophyll content (SPAD) reading, and a vegetation index measured by the optical sensor N-Sensor® ALS. The plants were evaluated in the stages V4, V6, V8, V10, V12 and at corn flowering. The experiments had a completely randomized design at three different sites that were analyzed separately. The vegetation index was directly related to above-ground dry matter production (R² = 0.91; p<0.0001), total N uptake (R² = 0.87; p<0.0001) and SPAD reading (R² = 0.63; p<0.0001) and inversely related to plant N content (R² = 0.53; p<0.0001). The efficiency of VRF for plant nutrition was influenced by the specific climatic conditions of each site. Therefore, the efficiency of the VRF strategy was similar to that of the standard farmer fertilizer strategy at sites 1 and 2. However, at site 3 where the climatic conditions were favorable for corn growth, the use of optical sensors to determine VRF resulted in a 12 % increase in N plant uptake in relation to the standard fertilization, indicating the potential of this technology to improve NUE.

Highlights

Corn yield is highly dependent on the level of agricultural technology and the quality of the crop management (Raun et al, 2011)
The high precipitation recorded in this period could affect corn nutrition due to the leaching of mineral N, removing this nutrient from the root zone
Site 2 had very low precipitation in the same period, which could compromise corn N uptake, since adequate soil moisture is essential for soil organic matter (SOM) mineralization and for the mass flux which is the main mechanism of N uptake (Barber, 1962; Sangoi & Almeida, 1994)

Summary

Introduction

Corn yield is highly dependent on the level of agricultural technology and the quality of the crop management (Raun et al, 2011). The spatial variability of the soil and crop properties in the field are not taken into account, which may impair an optimal plant nutrition. The risk of N leaching, notably under wet tropical and subtropical climate conditions, associated to the spatial variability of soil properties, such as: SOM content (Amado et al, 2009; Casa et al, 2011), horizon thickness (Albuquerque et al, 1996), water content (Delin & Berglund, 2005; Gregoret et al, 2006), and yield zones (Molin, 2001; Blackmore et al, 2003; Amado et al, 2009; Bramley, 2009) have effects on the N nutrition status of corn plants in the field. TSF could over-fertilize some sites while others could be underfertilized (Bredemeier & Schmidhalter, 2005), promoting low N fertilization efficiency and increasing environmental impacts (Raun et al, 2005)

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