Lincoln Zotarelli

Assimilation of SMOS Soil Moisture for Quantifying Drought Impacts on Crop Yield in Agricultural Regions

This study investigates the effects of agricultural drought on crop yields, through integration of crop growth models and remote sensing observations. The soil moisture (SM) product from SM and Ocean Salinity (SMOS) mission obtained at 25 km was downscaled to a spatial resolution of 1 km, compatible with the crop models. The downscaling algorithm is based upon information theoretic learning and uses data-driven probabilistic relationships between high-resolution remotely sensed products that are sensitive to SM and in situ SM. The downscaled SM values are assimilated in the crop model using an Ensemble Kalman filter-based augmented state-vector technique that estimates states and parameters simultaneously. The downscaling and assimilation framework are implemented for predominantly agricultural region of the lower La-Plata Basin (LPB) in Brazil during two growing seasons. This rain-fed region was affected by agricultural drought in the second season, indicated by markedly lower precipitation compared to the first growing season. The downscaled SM was compared with the in situ SM at a validation site and the root mean square difference (RMSD) was 0.045 m3/m3. The crop yields estimated by the downscaling-assimilation framework were compared with those provided by the Companhia Nacional de Asastecimento (CONAB) and Instituto Brasileiro de Geografia e Estatistica (IBGE). The assimilated yields are improved during both seasons with increased improvement during the second season that was affected by agricultural drought. The differences between the assimilated and observed crop yields were 16.8% during the first growing season and 4.37% during the second season.

Irrigation Scheduling for Green Bell Peppers Using Capacitance Soil Moisture Sensors

Vegetable production areas are intensively managed with high inputs of fertilizer and irrigation. The objectives of this study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling using soil moisture sensor irrigation controllers (SMS) on yield, irrigation water use efficiency (IWUE) of bell pepper cultivated under plastic mulch and drip irrigation. Treatments included three irrigation scheduling and three N-rates (176, 220, and 330 kg/ha). Irrigation treatments were: SS10 , water application controlled by SMS-based irrigation set at 10% volumetric water content (VWC) which was allotted five irrigation windows daily and bypassed events if the soil VWC exceeded the established threshold; SS12 , threshold set at 12% VWC; and TIME, control with irrigation being applied once a day similar to grower irrigation management. Marketable yields ranged between 16 and 29 Mg/ha. The SMS treatments reduced the applied irrigation in 7 to 62% compared to TIME treatment without reducing yi...

Reductions in a Commercial Potato Irrigation Schedule during Tuber Bulking in Florida: Physiological, Yield, and Quality Effects

Proper irrigation scheduling in potato (Solanum tuberosum L.) can lead to higher returns and more sustainable production practices when compared to systems that do not take plant water demand into account. In an attempt to reduce irrigation applications while minimizing yield reduction, we evaluated a novel deficit irrigation treatment utilizing a mild irrigation reduction during tuber bulking by comparing a typical commercial irrigation schedule to a partial irrigation schedule. Physiological, yield, and quality effects were quantified. Reducing the number of irrigation applications by 14 in 2011 and by 9 in 2012 minimally affected most parameters measured. However, a significant yield reduction of 11,713 kg/ha in the partial irrigation treatment occurred in 2011, likely because of the irrigation treatment commencing at the latter portion of tuber initiation. In 2012, the initiation of the partial irrigation was delayed and resulted in no significant difference in yield between the partial and full irrigation treatments. This study shows the potential for a reduced irrigation schedule for use by Florida potato growers as a sustainable option for potato production in this region.

Enhancing fertilizer efficiency in high input cropping systems in Florida

During the last century, a number of strategies have been used to determine optimal N-fertilizer rates and to develop appropriate N-fertilizer recommendations for intensively-managed cropping systems. However, these strategies lack a system-based approach and the precision needed to warrant high yields while addressing environmental concerns in a cost-effective manner. Therefore, a more holistic approach is required to enhance fertilizer use efficiency (FUE) in high input agricultural systems that pose both large environmental and economic risks. This article presents a physiological basis for improving FUE in these systems by linking physiological crop nutrient requirements with nutrient uptake efficiencies as affected by root characteristics, crop N demand, and production management practices. Starting at the crop and field level we outline key processes affecting crop N demand and uptake efficiency. For this purpose we reviewed key scientific papers that describe yield response and fertilizer uptake efficiencies with special reference to pepper (Capsicum annuum L.), potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum L.) crops in Florida production systems. This because such systems are especially prone to N leaching. Based on this review it is evident that yield response to fertilizer for most crops tend to be inconsistent both within and across locations. Therefore, use of standard recommendations may not be appropriate since they pose substantial economic and environmental risks.

Cover Crops in Agrosystems: Innovations and Applications

Cover crops can reduce the dependence of farmers on agrochemicals while enhancing overall agrosystem’s performance. However, the inherent complexity of cover-crop-based systems hampers their adoption by conventional farmers. Therefore, special management skills and alternative research and technology transfer approaches may be required to facilitate their adoptive use by conventional farmers. We propose that development and adoption of suitable cover-crop-based production systems may require the use of an “innovation framework” that includes (1) identification of system constraints, (2) analysis of system behavior, (3) exploration of alternative systems, and (4) system design and selection. We describe case studies from four regions of the Americas (Florida, USA; Parana and Santa Catarina, Brazil; and Canelones, Uruguay) that illustrate the relationships between this innovation framework and the development and adoption of cover-crop-based production systems. Where successful, development and adoption of such systems appear to relate to a number of attributes including (1) active involvement by farmers in research and dissemination programs; (2) integration of cover crops into production systems without net loss of land or labor resources; (3) informing farmers of the (direct) benefits of cover crop use; (4) provision of multiple benefits by cover crops, (5) sufficient access to information, inputs, and technologies required for cover crop use; and (6) provision of skills and experience necessary to manage cover crops effectively. Where these attributes are absent and failure to innovate has prevented development and adoption of cover-crop-based systems, policy initiatives to reward farmers for ecological services provided by cover crops may be required.

Nitrogen Uptake Efficiency and Growth of Bell Pepper in Relation to Time of Exposure to Fertilizer Solution

Irrigation of high‐value vegetable crops on sandy soils with poor water‐retention capacities may result in fertilizer nitrogen (N) displacement below the effective root zone prior to complete crop uptake. As a result, fertilizer N‐uptake efficiency (FUE) of vegetable crops is often relatively low, thereby increasing the potential risk of groundwater contamination. The objective of this study was to determine how time of exposure of the root zone to the N fertilizer (which is referred to as “fertilizer residence time” or t R), as related to irrigation management, affects N uptake, FUE, growth, and yield of bell pepper (Capsicum annuum L.). Plants were grown in PVC columns with 45 kg of soil equipped with a drainage valve in the bottom of the column. Weekly irrigation with dissolved fertilizers (potassium nitrate; KNO3) was applied 1, 3, or 7 d before weekly removal of residual soil N by leaching. Weekly N uptake rates were calculated by comparing total N recovery between unplanted (reference) and planted columns. At 77 d after planting, increasing the t R from 1 to 3 or 7 d increased the weekly N uptake from 1.4 to 10.8 and/or 13.3 kg N ha−1, respectively. Total calculated plant N accumulations were 19, 72, and 106 kg N ha−1 for the 1‐, 3‐, and 7‐d t R treatments, with overall FUE values being 8, 31, and 45%, respectively. It is concluded that during initial growth crop, uptake capacity is limiting, and more frequent (daily) fertilizer injection into the irrigation water may be required to enhance FUE. It is proposed also that via sound or innovative irrigation management practices, fertilizer retention in the root zone can be enhanced, thereby improving crop growth, yield, and FUE while reducing production cost and potential environmental impacts.

Irrigation and Nitrogen Best Management Practices Under Drip Irrigated Vegetable Production

Plastic mulch and drip irrigation are commonly used in high intensity vegetable production regions such as Florida. Drip irrigation can be much more efficient than sprinkler irrigation since only the root zone of the cropped area is irrigated. However, improper irrigation management can lead to wasted water and leaching of soluble chemicals such as nitrate. In this project, several irrigation treatments were established that allowed up to five watering events per day depending on a soil water threshold controller (SMS) for tomato and green bell pepper. As a comparison time based treatments (TIME) of once daily irrigation were established to mimic typical producer practices. In addition, zero tension drainage lysimeters were buried 0.6 m below the beds in several treatments to monitor leaching of water and nitrate nitrogen. SMS control of irrigation resulted in 29%-44% less irrigation water used on tomato and 37%-66% less water used on pepper when compared to TIME treatments. Tomato yield was significantly higher on SMS treatments compared to TIME treatments, but yield was similar across all pepper treatments. SMS treatments increased irrigation water use efficiency 2-3 times compared to TIME treatments on both tomato and pepper. Both the amount of water captured in drainage lysimeters and the mass on NO 3-N were significantly lower on soil water based irrigation control compared to once daily time based irrigation commonly used by producers.

Techniques for the Quantification of Plant-Associated Biological Nitrogen Fixation

There are many techniques available for the quantification of plant-associated biological nitrogen fixation (BNF) and they can be divided roughly into those that are applicable in the field and those that are not. This short review will mainly consider the former and we cite key references that should be consulted for further details. The techniques that are rarely applicable in the field include the acetylene-reduction assay, exposure to 15 N2enriched atmospheres and the total N-balance method.

BENEFIT OF LEGUME-FIXED N IN CROP ROTATIONS UNDER ZERO-TILLAGE

Under conventional tillage, although the contribution of BNF to soybean was high (190–315 kg N ha −1 ), more N was removed in the grain, resulting in a negative balance. Under no-tillage, the N balance was occasionally slightly positive. In the case of lupins, as no N was harvested from the system, there was a large N contribution to the subsequent maize crop. The no-till system favoured the retention of soil N and a higher BNF contribution to the legumes.

High Levels of Heterozygosity Found for 15 SSR Loci in Solanum chacoense

Wild species-related germplasm is widely used to introduce new alleles and/or increase heterozygosity in cultivated species. Twenty-four SSR markers, specifically designed for cultivated potatoes, were evaluated to determine the extent of genetic variation within and among ten accessions of Solanum chacoense (chc). Fifteen of these markers were informative: there was no polymorphism in one of the markers, four of the markers showed evidence that more than one locus was being amplified, and the other four markers failed to consistently amplify products. Heterozygosity in these 10 accessions ranged from 33% to 87%. Variation among accessions was the largest proportion of variance for three markers, variation among genotypes within accessions was the largest proportion for three markers, and for the other nine markers variation within genotypes (chromosome to chromosome) was the largest proportion. Genetic similarity averaged 29.5% across markers. Where accessions have already been screened and found to possess the trait of interest, multiple genotypes from those accessions should be evaluated to identify genotypes with the greatest expression of the trait.ResumenEl germoplasma relacionado a especies silvestres se usa ampliamente para introducir nuevos alelos y/o aumentar la heterozigocidad en especies cultivadas. Se evaluaron 24 marcadores SSR específicamente diseñados para papas cultivadas, para determinar la amplitud de la variación genética dentro y entre diez introducciones de Solanum chacoense (chc). Quince de estos marcadores fueron informativos: no hubo polimorfismo en uno de los marcadores, cuatro de ellos mostraron evidencia de que más de un locus estaba siendo amplificado, y los otros cuatro marcadores fallaron para amplificar consistentemente los productos. La eterozigocidad en estas diez introducciones varió de 33% a 87%. La variación entre las accesiones fue la proporción mas grande de varianza para tres marcadores, la variación entre genotipos dentro de las introducciones fue la de mayor proporción para tres marcadores, y para los otros nueve la variación dentro de genotipos (cromosoma a cromosoma) fue la proporción más grande. La similitud genética promedió 29.5% entre los marcadores. En donde las accesiones ya han sido analizadas y que se encontró que poseen el carácter de interés, múltiples genotipos de estas introducciones deberían evaluarse para identificar genotipos con la mayor expansión del carácter.