Site-specific Nitrogen Management Research Articles

Potential of RapidEye and WorldView-2 Satellite Data for Improving Rice Nitrogen Status Monitoring at Different Growth Stages

For in-season site-specific nitrogen (N) management of rice to be successful, it is crucially important to diagnose rice N status efficiently across large areas within a short time frame. In recent studies, the FORMOSAT-2 satellite images with traditional blue (B), green (G), red (R), and near-infrared (NIR) wavebands have been used to estimate rice N status due to its high spatial resolution, daily revisit capability, and relatively lower cost. This study aimed to evaluate the potential improvements of RapidEye and WorldView-2 data over FORMOSAT-2 for rice N status monitoring, as the former two sensors provide additional wavelengths besides the traditional four wavebands. Ten site-year N rate experiments were conducted in Jiansanjiang, Heilongjiang Province of Northeast China from 2008 to 2011. Plant samples and field hyperspectral data were collected at three growth stages: panicle initiation (PI), stem elongation (SE), and heading (HE). The canopy-scale hyperspectral data were upscaled to simulate the satellite bands. Vegetation index (VI) analysis, stepwise multiple linear regression (SMLR), and partial least squares regression (PLSR) were performed to derive plant N status indicators. The results indicated that the best-performed VIs calculated from the simulated RapidEye and WorldView-2 bands, especially those based on the red edge (RE) bands, explained significantly more variability for above ground biomass (AGB), plant N uptake (PNU), and nitrogen nutrition index (NNI) estimations than their FORMOSAT-2-based counterparts did, especially at the PI and SE stages. The SMLR and PLSR models based on the WorldView-2 bands generally had the best performance, followed by the ones based on the RapidEye bands. The SMLR results revealed that both the NIR and RE bands were important for N status estimation. In particular, the NIR1 band (760–900 nm from RapidEye or 770–895 nm from WorldView-2) was most important for estimating all the N status indicators. The RE band (690–730 nm or 705–745 nm) improved AGB, PNU, and NNI estimations at all three stages, especially at the PI and SE stages. AGB and PNU were best estimated using data across the stages while plant N concentration (PNC) and NNI were best estimated at the HE stage. The PLSR analysis confirmed the significance of the NIR1 band for AGB, PNU, and NNI estimations at all stages except for the HE stage. It also showed the importance of including extra bands (coastal, yellow, and NIR2) from the WorldView-2 sensor for N status estimation. Overall, both the RapidEye and WorldView-2 data with RE bands improved the results relative to FORMOSAT-2 data. However, the WorldView-2 data with three extra bands in the visible and NIR regions showed the highest potential in estimating rice N status.

Improving in-season estimation of rice yield potential and responsiveness to topdressing nitrogen application with Crop Circle active crop canopy sensor

In-season site-specific nitrogen (N) management is a promising strategy to improve crop N use efficiency and reduce risks of environmental contamination. To successfully implement such precision management strategies, it is important to accurately estimate yield potential without additional topdressing N application (YP0) as well as precisely assess the responsiveness to additional N application (RI) during the growing season. Previous research has mainly used normalized difference vegetation index (NDVI) or ratio vegetation index (RVI) obtained from GreenSeeker active crop canopy sensor with two fixed bands in red and near-infrared (NIR) spectrums to estimate these two parameters. The development of three-band Crop Circle active sensor provides a potential to improve in-season estimation of YP0 and RI. The objectives of this study were twofold: (1) identify important vegetation indices obtained from Crop Circle ACS-470 sensor for estimating rice YP0 and RI; and (2) evaluate their potential improvements over GreenSeeker NDVI and RVI. Four site-years of field N rate experiments were conducted in 2012 and 2013 at the Jiansanjiang Experiment Station of China Agricultural University located in Northeast China. The GreenSeeker and Crop Circle ACS-470 active canopy sensor with green, red edge, and NIR bands were used to collect rice canopy reflectance data at different key growth stages. The results indicated that both the GreenSeeker (best R2 = 0.66 and 0.70, respectively) and Crop Circle (best R2 = 0.71 and 0.77, respectively) sensors worked well for estimating YP0 and RI at the stem elongation stage. At the booting stage, Crop Circle red edge optimized soil adjusted vegetation index (REOSAVI, R2 = 0.82) and green ratio vegetation index (R2 = 0.73) explained 26 and 22 % more variability in YP0 and RI, respectively, than GreenSeeker NDVI or RVI. At the heading stage, the GreenSeeker sensor indices became saturated and consequently could not be used for YP0 or RI estimation, while Crop Circle REOSAVI and normalized green index could still explain more than 70 % of YP0 and RI variability. It is concluded that both sensors performed similarly at the stem elongation stage, but significantly better results were obtained by the Crop Circle sensor at the booting and heading stages. Furthermore, the results revealed that Crop Circle green band-based vegetation indices performed well for RI estimation while the red edge-based vegetation indices were the best for estimating YP0 at later growth stages.

Review: Nitrogen Utilization Features in Cotton Crop

Cotton is one of the important cash crops and a fiber crop most widely grown and the highest yielding as well. Cotton fiber is woven to be the fabrics commonly used in our daily life due to its excellent performance and great production in the world, especially in China. To access to such high quantities must ensure the requirements of materials such as nutrients for plant growth and take care of the smallest details to make the production cost less, to improve the utilization efficiency, such as nitrogen (N) fertilizer. Hence, N fertilization studies are not only about the dosages, timing and ratio, but also the uptake processes by the plant, N effect on cotton yield and its formation, as well as the movement and metabolism within the plant. As economic and ecological issues are concerned, economizing N fertilization is paid more and more attention. Many approaches have been done and suggested in order to improve NUE like combine the plant sensing techniques and precision application. Simulations and recent field trials demonstrate that site-specific nitrogen management helped reduce technological constraints to higher AE achievement, profit and more sustainable N management. Therefore, improving nitrogen use efficiency (NUE) is one of the key points to ensure cotton production development sustainable. In this review, we try to highlight the accomplishments of N effect on cotton growth and yield, NUE and factors related to NUE in cotton production based on the current knowledge, and from our viewpoint we propose some possible approaches to improve NUE through N managements in terms of application splits, rates, and timing.

Active canopy sensing of winter wheat nitrogen status: An evaluation of two sensor systems

Crop canopy sensor based in-season site-specific nitrogen (N) management is a promising approach to precision N management. GreenSeeker sensor has previously been evaluated in North China Plain (NCP) for improving winter wheat (Triticum aestivum L.) N management. The Crop Circle ACS-470 is an active canopy sensor with three user-configurable wavebands. This study identified important vegetation indices that can be calculated from Crop Circle green, red edge and near infrared (NIR) wavebands for estimating winter wheat N status and evaluated their potential improvements over GreenSeeker normalized difference vegetation index (NDVI) and ratio vegetation index (RVI). Six field experiments involving different N rates and varieties were conducted in the Quzhou Experiment Station of the China Agricultural University from 2009 to 2012. The results indicated that best Crop Circle ACS-470 sensor vegetation indices could explain similar amounts of aboveground biomass variability in comparison with GreenSeeker sensor NDVI, but Crop Circle normalized difference red edge/green optimized soil adjusted vegetation index (NDRE/GOSAVI) and red edge chlorophyll index (CIRE) were more sensitive to aboveground biomass (having lower noise equivalent) than GreenSeeker NDVI before and after biomass reached about 5000kgha−1, respectively. The Crop Circle green difference vegetation index (GDVI) (R2=0.60) and chlorophyll index (CIG) (R2=0.89) explained 53% and 7–11% more variability in plant N concentration and uptake than GreenSeeker indices, respectively. The Crop Circle green re-normalized difference vegetation index (GRDVI) (R2=0.78) and modified green soil adjusted vegetation index (MGSAVI) (R2=0.77) performed consistently better than GreenSeeker NDVI (R2=0.47) and RVI (R2=0.44) for estimating N nutrition index (NNI). We conclude that the three band user configurable Crop Circle ACS-470 sensor can improve the estimation of winter wheat N status as compared with two fixed band GreenSeeker sensor.

Maize (Zea mays L.) Growth and Grain Yield under Conventional and Site-Specific Nitrogen Management in a Dryland Farming System

Maize (Zea mays L.) Growth and Grain Yield under Conventional and Site-Specific Nitrogen Management in a Dryland Farming System

Combination of site-specific nitrogen management and alternate wetting and drying irrigation increases grain yield and nitrogen and water use efficiency in super rice

Site-specific nitrogen management (SSNM) and alternate wetting and drying (AWD) irrigation are two applied technologies developed in recent years in rice production. Little is known, however, how synergistic these two technologies can be in terms of grain yield, nitrogen and water use efficiencies. We investigated this issue using super rice under SSNM, AWD, or both. Two super rice varieties subjected to four N and irrigation treatments, i.e., continuously flooded (CF) and farmer's N practice (FNP) (CF-FNP), CF-SSNM, AWD-FNP, and AWD-SSNM, were field-grown in 2011 and 2012. SSNM or AWD significantly increased the percentage of productive tillers, leaf area duration, leaf photosynthetic rate, root oxidation activity and dry matter accumulation during grain filling compared with FNP or CF. Such increases were more evident when both AWD and SSNM were adopted together. The AWD-SSNM treatment increased not only the number of spikelets per panicle, but also the percentage of filled grains and grain weight. Root biomass at heading time and the harvest index were significantly higher under the AWD-SSNM treatment than those under any other treatments. When compared to those under the CF-FNP treatment, grain yield, N partial factor productivity (grain yield over the N rate) and WUE (grain yield over the amount of irrigation water and rainfall) under the SSNM-AWD treatment were increased by 12.4–14.5%, 26.5–30.7% and 22.8–26.7%, respectively, and also significantly higher than those under SSNM or AWD alone. The results suggest that synergistic interaction between SSNM and AWD occurs in the yield formation, and such an interaction could increase not only grain yield, but also resource-use efficiency in super rice.

Characteristics of Nutrient Uptake and Accumulation in Wheat and Rice with Continuous Cropping under Super-High-Yielding Cultivation

Understanding characteristics of nutrient uptake and accumulation in plants would be highly significant in the realization of high-yielding and high efficiency of resource use in rice and wheat. This study aimed at investigating uptake and accumulation characteristics of nitrogen (N), phosphorous (P), and potassium (K) in rice and wheat plants under super-high-yielding cultivation in the wheat-rice planting system in the lower reaches of Yangtze River of China. Two high-yielding wheat varieties and two rice varieties were field-grown for two years. Two cultivation patterns, the local farmers’ practice and super-high-yielding cultivation, were used. The super-high-yielding cultivation adopted two new key techniques, i.e., site-specific nitrogen management and alternate wetting and moderate drying irrigation in rice and controlled soil drying irrigation in wheat. In comparison with those under the local farmers’ practice (wheat yield 8t ha-1 and rice yield 9t ha-1), the total uptake of N, P, or K in plants was significantly increased, and the accumulation of N, P, or K was significantly decreased before stem elongation, whereas it was significantly increased in the durations from the stem elongation to flowering and from flowering to maturity under the super-high-yielding cultivation (wheat yield 9t ha-1 and rice yield 12t ha-1). The total uptake of N, P, and K under the super-high-yielding cultivation was 265, 58, and 256 kg ha-1 for wheat and 256, 79, and 321 kg ha-1 for rice, respectively. The proportion of N, P, or K accumulated in plants during the mid and late growth period (from stem elongation to maturity) to the total uptake of nutrients was 50–60% for wheat and 60–70% for rice. The super-high-yielding cultivation significantly increased partial factor productivity of N, P, or K (grain yield/amount of N, P, or K applied), internal nutrient efficiency (grain yield/total uptake of N, P, or K at maturity), and harvest index of nutrients (uptake of N, P, or K in grains/the total uptake of N, P, or K in plants at maturity), and significantly decreased the absorption amount of nutrients for grain production (total uptake of N, P, or K in plants at maturity/grain yield). The results suggest that both wheat and rice absorb relatively smaller nutrients at early growth stages and more nutrients during the mid and late growth period, and the uptake and use efficiency of nutrients could be increased under the super-high-yielding cultivation.

Agronomic and physiological performance of high-yielding wheat and rice in the lower reaches of Yangtze River of China

Understanding agronomic and physiological performance of crop high yield is essential to make strategies for breeding and crop management. This study aimed to identify major agronomic and physiological traits associated with high grain yields of rice and wheat in the wheat–rice rotation system in the lower reaches of Yangtze River of China. Two high-yielding cultivars, each for winter wheat and rice, were field-grown from 2008 to 2010 for 3 years. Two crop management treatments, the local farmer's practice (LFP) and improved high-yielding cultivation (IHC), were used. The IHC adopted two new techniques, i.e., site-specific nitrogen management in both rice and wheat and alternate wetting and moderate drying irrigation in rice and controlled soil drying irrigation in wheat. Across the 3 years, the IHC yielded an average 9.67tha−1 of wheat and 12.55tha−1 of rice with an annual total of 22.2tha−1, an increase of 26.8% when compared with that (17.5tha−1) under the LFP. The increased grain yield under the IHC was mainly attributed to expanded sink size as a result of more kernels per spike or more spikelets per panicle, increased kernel weight of wheat and increased percentage of filled grains of rice. When compared with LFP, IHC showed a greater percentage of productive tillers, more pre-anthesis nonstructural carbohydrate (NSC) storage in the stem, greater leaf photosynthetic rate and concentration of cytokinins in root exudates, higher activities of sucrose synthase and adenosine diphosphoglucose pyrophosphorylase in grains, more dry mater production during the grain filling period, and higher harvest index. We conclude that (1) expanding sink capacity through an increase in kernels per spike or spikelets per panicle, (2) enhancing grain filling efficiency by an increase in pre-anthesis NSC in the stem, and (3) increasing post-anthesis dry mater production by an enhancement in root activity during grain filling should be considered as three major strategies for further increases in grain yields of wheat and rice in the lower reaches of Yangtze River of China.

Site Specific Nitrogen Management Simulated by CropSyst Model under Different Inputs of Nitrogen Fertilizer

Site Specific Nitrogen Management Simulated by CropSyst Model under Different Inputs of Nitrogen Fertilizer (Y Wijayanto): Site Specific Nutrient Management (SSNM) has been suggested as the only means for increasing productivity of crops and minimizing the environmental impacts. Despite of this, it is also widely recognized that compared to uniform application, SSNM provides a significant challenges related to the level of management. This is due to the fact that SSNM relates to the management of field / site (or fields / sites) and considers also the spatial and temporal component of factors leading to crop production. A method is urgently required and the most appropriate one is crop model. This study was aimed at using CropSyst to model yields due to the difference in N applications and its implementation for SSNM. The study area was located at Jenggawah Village, Sub-District Jenggawah, Jember Regency. Thirty soil samples were taken and six farmer’s fields were chosen for the purpose of modeling. Interview was conducted to obtain the information about the management of farmer’s fields. Yields in each farmer’s fields were used as an integrated indicator. The results suggested that the predicted yields at farmer’s fields were in agreement with those in reality. Simulated yields based on different amount of N inputs showed yields were proportional with different N inputs. This study concluded that there do exist a significant amount of potential applications of CropSyst for Site Specific Nitrogen Management

Site Specific Nitrogen Management Simulated by CropSyst Model under Different Inputs of Nitrogen Fertilizer

Population and diversity of arbuscular mycorrhiza fungi (AMF) are varied in the soil and influenced by biotic factors such as host plant and abiotic factors such as soil fertility, soil moisture, pH, temperature, etc. This study aimed to determine the population, diversity, and the dominant type of AMF in the rhizosphere of Kasetsart cassava clones obtained from LampungTimur and Tulang Bawang Barat Regencies, Lampung Province, Indonesia. Population of AMF was counted directly from the rhizosphere of Kasetsart cassava clones and the diversity of AMF was assesed using a pot culture experiment. The results showed that the population and the diversity of AMF in the rhizosphere of Kasetsart clone obtained from Tulang Bawang Barat was higher than that from LampungTimur. The predominant type of AMF found in the pot culture using soil samples from Lampung Timur was spore with S2 code that belongs to the genus Gigaspora and S4 code that belongs to the genus Glomus. On the other hand, the type of AMF found in the rhizosphere of soil samples from Tulang Bawang Barat was dominated by spore with S9 code that belongs to the genus Entrophospora.

Spatial Variability of Soil Nutrients Content Related to Rice Yield

Site Specific Nitrogen Management Simulated by CropSyst Model under Different Inputs of Nitrogen Fertilizer (Y Wijayanto): Site Specific Nutrient Management (SSNM) has been suggested as the only means for increasing productivity of crops and minimizing the environmental impacts. Despite of this, it is also widely recognized that compared to uniform application, SSNM provides a significant challenges related to the level of management. This is due to the fact that SSNM relates to the management of field / site (or fields / sites) and considers also the spatial and temporal component of factors leading to crop production. A method is urgently required and the most appropriate one is crop model. This study was aimed at using CropSyst to model yields due to the difference in N applications and its implementation for SSNM. The study area was located at Jenggawah Village, Sub-District Jenggawah, Jember Regency. Thirty soil samples were taken and six farmer’s fields were chosen for the purpose of modeling. Interview was conducted to obtain the information about the management of farmer’s fields. Yields in each farmer’s fields were used as an integrated indicator. The results suggested that the predicted yields at farmer’s fields were in agreement with those in reality. Simulated yields based on different amount of N inputs showed yields were proportional with different N inputs. This study concluded that there do exist a significant amount of potential applications of CropSyst for Site Specific Nitrogen Management

Development of SPAD Values of Medium- and Long-duration Rice Variety for Site-specific Nitrogen Management

Development of SPAD Values of Medium- and Long-duration Rice Variety for Site-specific Nitrogen Management

Narrowing the agronomic yield gap with improved nitrogen use efficiency: a modeling approach

Improving nitrogen use efficiency (NUE) in the major cereals is critical for more sustainable nitrogen use in high-input agriculture, but our understanding of the potential for NUE improvement is limited by a paucity of reliable on-farm measurements. Limited on-farm data suggest that agronomic NUE (AE(N)) is lower and more variable than data from trials conducted at research stations, on which much of our understanding of AE(N) has been built. The purpose of this study was to determine the magnitude and causes of variability in AE(N) across an agricultural region, which we refer to as the achievement distribution of AE(N). The distribution of simulated AE(N) in 80 farmers' fields in an irrigated wheat system in the Yaqui Valley, Mexico, was compared with trials at a local research center (International Wheat and Maize Improvement Center; CIMMYT). An agroecosystem simulation model WNMM was used to understand factors controlling yield, AE(N), gaseous N emissions, and nitrate leaching in the region. Simulated AE(N) in the Yaqui Valley was highly variable, and mean on-farm AE(N) was 44% lower than trials with similar fertilization rates at CIMMYT. Variability in residual N supply was the most important factor determining simulated AE(N). Better split applications of N fertilizer led to almost a doubling of AE(N), increased profit, and reduced N pollution, and even larger improvements were possible with technologies that allow for direct measurement of soil N supply and plant N demand, such as site-specific nitrogen management.

Effects of Wheat-Residue Application and Site-Specific Nitrogen Management on Growth and Development in Direct-Seeding Rice

The annual total amount of crop residue straw exceeds billion tons in China. However, about 45–60% of them are burnt or discarded, which not only wastes organic fertilizer source, but also pollutes the environment. Meanwhile, heavy use of nitrogen fertilizer has become a serious problem in rice production. The objective of this study was to investigate the effects of wheat straw incorporation to soil and site-specific nitrogen management (SSNM) on the growth and development in direct-seeding rice. A mid-season japonica rice cultivar Yangjing 9538 was directly sown in field with three nitrogen (N) fertilizer treatments, no N application, farmers’ fertilizer-N practice (FFP), and SSNM based on chlorophyll meter (SPAD) readings. The results showed that, compared with FFP, SSNM reduced N application by 30.0–31.3% and increased grain yield by 7.61%, on average. The grain yield in the wheat residue-incorporated treatment was 2.65%, on average, higher than that in the residue-removed treatment. In comparison with those under the residue removal and FFP, the number of stems and tillers, leaf area index, and biomass accumulation were less or lower under the residue incorporation and SSNM during the early growth period, but showed no significant difference at heading and thereafter. The residue incorporation increased the content of organic acid in leaves and the difference in temperature and relative humidity between day and night. Both the residue incorporation and SSNM increased the percentage of productive tillers, photosynthetic rate of the flag leaves, root activity, and ATPase activity during grain filling. The results suggest that both the residue incorporation and SSNM benefit the photosynthetic production of direct-seeding rice during the later growth period and an increase in the production efficiency. Reasons for the characteristics of the grain yield, growth and development under the residue incorporation and SSNM were discussed.

Effects of Wheat Residue Application and Site-Specific Nitrogen Management on Growth and Development in Direct-Seeding Rice

The objective of this study was to investigate the growth and development of rice ( Oryza sativa L.) under the treatments of wheat ( Triticum aestivum L.) residue incorporation (RI) and nitrogen (N) fertilizer application. A mid-season japonica rice cultivar Yangjing 9538 was directly sown in field. Either in RI treatment or in the treatment with no residue return to field (R0), 3 nitrogen (N) fertilizer application levels were carried out, i.e., no N application, farmers' fertilizer practice (FFP), and site-specific N management (SSNM). The SSNM was based on chlorophyll meter readings in field. Compared with FFP, SSNM reduced N application by 30.0–31.3% and increased grain yield by 7.61% on an average. The average grain yield was 2.65% higher in the RI treatment than in the R0 treatment. Compared with the R0 or FFP treatment, the RI or SSNM treatment decreased stem and tiller numbers, leaf area index, and biomass accumulation at early growing period, but the differences were not significant after heading stage. RI was favorable for increasing the content of organic acid in leaves and enlarging the variations of temperature and relative humidity between day and night. The RI and SSNM treatments had positive effects on the percentage of productive tillers, photosynthetic rate of flag leaf, root activity, and ATPase activity during grain-filling stage.

Effects of Wheat-Residue Application and Site-Specific Nitrogen Manage-ment on Absorption and Utilization of Nitrogen, Phosphorus, and Potassium in Rice Plants

Effects of Wheat-Residue Application and Site-Specific Nitrogen Manage-ment on Absorption and Utilization of Nitrogen, Phosphorus, and Potassium in Rice Plants

Combining chlorophyll meter readings and high spatial resolution remote sensing images for in-season site-specific nitrogen management of corn

The chlorophyll meter (CM) has been commonly used for in-season nitrogen (N) management of corn (Zea mays L.). Nevertheless, it has limited potential for site-specific N management in large fields due to difficulties in using it to generate N status maps. The objective of this study was to determine how well CM readings can be estimated using aerial hyper-spectral and simulated multi-spectral remote sensing images at different corn growth stages. Two field experiments were conducted in Minnesota, USA during 2005 involving different N application rates and timings on a corn-soybean [Glycine max (L.) Merr.] rotation field and a corn-corn rotation field. Four flights were made during the growing season using the AISA Eagle Hyper-spectral Imager and CM readings were collected at four or five different growth stages. The results indicated that single multi-spectral and hyper-spectral band or vegetation index could explain 64–86% and 73–88% of the variability in CM readings, respectively, except at growth stage V9 in the corn-soybean rotation field where no band or vegetation index could explain more than 37% of the variability in CM readings. Multiple regression analysis demonstrated that the combination of 2–4 broad-bands or 3–8 narrow-bands could explain 41–92% or 61–94% of the variability in CM readings across the two fields and different corn growth stages investigated. It was concluded that the combination of CM readings with high spatial resolution hyper-spectral or multi-spectral remote sensing images can overcome the limitations of using them individually, thus offering a practical solution to N deficiency detection and possibly in-season site-specific N management in large continuous corn fields or at later stages in corn-soybean rotation fields.

Absorption and Utilization of Nitrogen, Phosphorus, and Potassium in Rice Plants Under Site-Specific Nitrogen Management and Wheat-Residue Incorporation

To investigate the absorption and utilization of major nutrient elements of rice ( Oryza sativa L.) plant when wheat ( Triticum aestivum L.) residues returned to the field (residue incorporation, RI) or under site-specific nitrogen management (SSNM), the effects of RI and SSNM on harvest index, translocation, and transportation efficiency were evaluated in 2005–2006, using a midseason japonica rice cultivar of Yangjing 9538. The results showed that under same N level, compared with the no straw incorporation, RI reduced N content and the accumulations of N, phosphorus (P), and potassium (K) in rice plants at the early growth stage but maintained high levels of contents of P and K during the whole growth period. Moreover, RI improved the N use efficiency and the harvest index and biomass production efficiency of N, P, and K. Under RI with the same amount of wheat residues, rice plants in SSNM had less absorption of N and P than in the N fertilizer rate in farmer practice (FFP). However, the transportation percentages of N, P, and K from heading to maturity, as well as the harvest indices of N and P under SSNM, were higher than those under FFP. The results indicate that both RI and SSNM can increase the absorptions and use efficiencies of N, P, and K in rice plants, and their combination shows better effects.

Evaluation of current and model-based site-specific nitrogen applications on wheat (Triticum aestivum L.) yield and environmental quality

Crop growth models have been used in the past to study causes of yield variability and to estimate the economic consequences of variable nitrogen rate prescriptions. In this study, the APOLLO model, which is based on the DSSAT crop growth model family, was implemented to develop optimum site-specific nitrogen management prescriptions for wheat. The nitrogen prescription was targeted to maximize the long-term marginal net return, which includes an economic penalty for leaving excess nitrogen in the root zone at harvest. By using two constraints—yield and environmental quality—it is expected that the simulation can find prescriptions that maximize marginal net return while reducing the amount of nitrogen losses to surface and groundwater sources at the sub-field scale. Overall, the total amount of nitrogen applied in the control and the model-based treatment was about the same. Thus, for yield, environmental aspects and economic aspects no significant differences were identified between both treatments. However, the results indicated that the model-based nitrogen prescription considered the yield variability adequately for most grids, given by an increase in nitrogen use efficiency, and thus enabled the design of nitrogen prescriptions adapted to the nitrogen demand of the plants. The model-based nitrogen strategy helps to optimize the nitrogen application rate within the field over the long-term of about 30 years. To gain further advantages from model-based nitrogen prescriptions, it seems to be useful to additionally update the model with actual information derived for the current growing conditions.

COMPORTAMENTO TEMPORAL DO NDVI MENSURADO COM SENSOR ÓPTICO ATIVO PARA DIFERENTES VARIEDADES DE CANA-DE-AÇÚCAR

Activeoptical sensors are a new approach for site specific nitrogen management on real time andthey have been successfully used on grain crops. This work consisted in evaluating the behaviorof the Normalized Difference Vegetation Index (NDVI) using a commercial active optical sensor on28 sugarcane varieties, as well as analyzing the temporal behavior of this index for each varietythroughout the initial 150 days of their productive cycle. The NDVI data was collected with 90, 120and 150 days after planting (DAP). A descriptive statistical analysis of the data was performed anda Tukey test was applied to contrast the NDVI means. Results indicated that the varieties interferein the NDVI readings and, in general, the readings with 90 DAP were different from those with 120and 150 DAP, tending to stabilize along time for each variety.