The Data-Intensive Farm Management (DIFM) project works with participating farmers, using precision technology to inexpensively design and run randomized agronomic field trials on whole commercial farm fields, to provide data-based, site-specific farm input management guidance, thus providing economic and environmental benefits. This article lays out a conceptual framework used by the multidisciplinary DIFM research team to facilitate collaboration and then presents details of DIFM's procedures for what it calls on-farm precision experimentation (OFPE), which includes field trial design and implementation, data generation, processing, and management, and analysis. It is argued that DIFM's data and the agricultural "Big Data" currently being collected with remote and proximal sensors are complementary; that is, more of either increases the value of the other. In 2019, DIFM and affiliates conducted over 120 trials, ranging from 10 to 100 ha in size, on maize, wheat, soybeans, cotton, and barley in eight US states, Argentina, Brazil, and South Africa. The DIFM project is developing cyberinfrastructure to "scale up" its activities, to permit researchers and crop consultants worldwide to work with farmers to conduct trials, then process and manage the data. In Addition, DIFM is in the early stages of developing a software system for semiautomatic data analytics, and a cloud-based farm management aid, the purpose of which is to facilitate conversations between agronomists and farmers about implementing data-driven input management decisions. The proposed framework allows researchers, agronomists, and farmers to carry out on-farm precision experimentation using novel digital tools.

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Resumo -O objetivo deste trabalho foi avaliar, numa perspectiva espacial, a resposta do milho (Zea mays) à adubação de cobertura com nitrogênio (N) e relacionar a produtividade de grãos com variáveis indicadoras do suprimento desse nutriente. Quatro doses de N foram testadas em 12 parcelas experimentais de 12,6x1.200 m. Em cada parcela foram georreferenciados 11 locais onde foram feitas as avaliações. Nesses locais, foi monitorado o estado nutricional do milho com o clorofilômetro e foram determinados os teores de N mineral do solo e os teores de N na folha e nos grãos. A produtividade de grãos foi mapeada com sensor de produtividade e "Global Positioning System" (GPS) acoplados à colhedora. Os dados foram analisados por estatística clássica e espacial. O cultivo sem aplicação de N em cobertura proporcionou, em média, 77% da máxima produtividade de milho (9,21 Mg ha -1 ) obtida com a adubação de cobertura. Altas correlações entre leitura do clorofilômetro, teor foliar de N e produtividade do milho, verificadas na análise de médias, não se confirmaram nos mapas que representam a variabilidade espacial dessas variáveis. A interpretação conjunta dos mapas de leitura do clorofilômetro e de produtividade do milho permitiu identificar áreas com diferentes capacidades de suprimento de N pelo solo e subsidiar a delimitação de zonas para o manejo diferenciado do nitrogênio.Termos para indexação: Zea mays, agricultura de precisão, clorofilômetro, escala de campo, manejo sítio-específico, nitrogênio. Spatial variation of corn response to nitrogen topdressing in a Cerrado crop fieldAbstract -The objective of this work was to evaluate the spatial variation of corn response to nitrogen (N) topdressing fertilization, associating the grain yield with indicative variables of the N nutritional status. Four N rates were tested in 12 experimental plots of 12.6x1,200 m. Along each plot, 11 georeferenced sites were located for punctual evaluations. In those sites, the corn nutritional status was monitored using a chlorophyll meter and samples were collected to determine soil mineral N, and N concentration in leaves and grains. The grain yield was mapped using a yield sensor and a Global Positioning System (GPS) device coupled to the combine. The data obtained were analyzed using classical and spatial statistics. The corn with no N topdressing reached an average of 77% of the maximum grain yield (9.21 Mg ha -1 ) obtained with the usage of topdressing. The high correlation coefficients among the average data of chlorophyll meter readings, leaf N content, and grain yield were not confirmed when the spatial variability of these variables were considered. The map interpretation of the chlorophyll meter readings and corn yield allowed the identification of areas with different soil N supply capacity, indicating field zones for site-specific management.

Resumo -Stylosanthes macrocephala M. B. Ferr. et S. Costa é uma leguminosa utilizada sob consorciação em pastagens, adubação e recuperação de áreas degradadas. A falta de características morfológicas e agronômicas estáveis e de informações ecogeográficas dos locais de coleta dos acessos tem dificultado o melhoramento genético da espécie. A fim de obter descritores ecológicos, moleculares e avaliar a variabilidade genética da coleção de S. macrocephala, 87 acessos foram analisados com o auxílio do Sistema de Informações Geográficas (SIG) e de marcadores moleculares RAPD. Os acessos provieram de sete Estados, cinco bacias hidrográficas, sete tipos de vegetação e sete tipos de solos. As altitudes dos locais de coleta variaram de 1 a 1.298 m e a pluviometria anual média de 550 a 2.870 mm. A variabilidade de descritores ecológicos sugeriu diversidade adaptativa na coleção. Com base em 161 marcadores RAPD, verificou-se que as distâncias genéticas entre os acessos de S. macrocephala variaram entre 0,02 e 0,42. Com base nessas distâncias, dez grupos de similaridade genética foram estabelecidos. Observou-se tendência de separação por bacias hidrográficas e elevada variabilidade genética entre os acessos coletados nos estados da Bahia e de Minas Gerais. A alta variabilidade genética da coleção de S. macrocephala evidencia a importância desses acessos para futuros trabalhos de melhoramento genético.Termos para indexação: diversidade genética, marcadores moleculares, germoplasma, leguminosa forrageira, Sistema de Informação Geográfica. Genetic and ecological variability of Stylosanthes macrocephala determined by RAPD markers and GISAbstract -Stylosanthes macrocephala M. B. Ferr et S. Costa is a leguminous species used as forage, cover crop and as a pioneer plant to recover degraded areas. Inexistence of stable morphological descriptors and lack of ecogeographic information about collecting sites bring difficulties to the studies of this species. The objective of this work was to use the geographic information system (GIS) and RAPD markers to obtain ecological and molecular descriptors and to study the genetic variability of 87 S. macrocephala accessions. The accessions were collected from different ecogeographical areas in seven Brazilian States, five hydrographic regions, seven vegetation types and seven soil types. Collecting sites ranged from 1 to 1,298 m above sea level with annual rainfall from 550 to 2,870 mm. Accession distribution along those diverse ecosystems indicate high adaptive diversity. Using 161 RAPD markers, genetic distances between accessions ranged from 0.02 to 0.42. These genetic distances allowed the establishment of ten genetic groups. Accessions collected in specific hydrographic region tended to be grouped in the same genetic group. Accessions collected in Bahia and Minas Gerais States showed high genetic variability. The high genetic variability observed in the accessions showed the importance of this S. macrocephala collection for breeding programs.

Much of the previous evaluation of active crop canopy sensors for in-season assessment of crop N status has occurred in environments without water stress. Th e impact of concurrent water and N stress on the use of active crop canopy sensors for in-season N management is unknown. Th e objective of this study was to evaluate the performance of various spectral indices for sensing N status of corn (Zea mays L.), where spectral variability might be confounded by water-induced variations in crop refl ectance. Th e study was conducted in 2009 and 2010 with experimental treatments of irrigation level (100 and 70% evapotranspiration [ET]), previous crop {corn-corn or soybean [Glycine max (L.) Merr.]-corn} and N fertilizer rate (0, 75, 150, and 225 kg N ha -1 ). Crop canopy refl ectance was measured from V11 to R4 stage using two active sensors-a two band (880 and 590 nm) and a three band (760, 720, and 670 nm). Among the indices, the vegetation index described by near infrared minus red edge divided by near infrared minus red (DATT) and Meris terrestrial chlorophyll index (MTCI) were the least aff ected by water stress, with good ability to diff erentiate N rate with both previous crops. Th e chlorophyll index using amber band (CI), normalized diff erence vegetation index using red edge band (NDVI_RE) and the normalized vegetationi using the red band (NDVI_Red) showed more variation due to water supply, and had only moderate ability to diff erentiate N rates. ).Abbreviations: ACS, active crop canopy sensors; CC, irrigated corn aft er corn; CI, chlorophyll index vegetation index using amber and near infrared; CIRE, chlorophyll index vegetation index using red edge and near infrared; CS, irrigated corn aft er soybean; DATT, vegetation index calculated using near infrared, red edge, and red bands published by Datt (1999); ET, evapotranspiration; MTCI, Meris terrestrial chlorophyll index; NDVI_RE, normalized diff erence vegetation index using the red edge band; NDVI_Red, normalized diff erence vegetation index using the red band; NIR, near infrared; NSI, nitrogen suffi ciency index.