Significant Yield Response Research Articles

Corn response to incremental applications of sulfate‐sulfur

AbstractReports of sulfur (S) deficiency symptoms in corn (Zea mays L.) fields of the Red River Valley of North Dakota and Minnesota are increasing. Current soil tests cannot predict the availability of S correctly due to the presence of gypsum in soils of this region. Field trials were conducted to determine corn yield and S uptake response to incremental applications of S (0, 11, 22, 33, and 44 kg S ha–1) in the form of ammonium sulfate [(NH4)2SO4]. Corn yield and S uptake varied significantly between sites. Out of 12 sites, only two sites had the highest corn yield without S application. Corn grain S removal ranged between 11 and 17 kg S ha–1 at harvest. Fertilizer‐S (SO4) application did not result in a significant yield response. The current recommendation of 11 kg S ha–1 may be necessary to reduce the risk of future S deficiency across this region and compensate for the removal of S in grain due to the uncertainty of adequate plant available S.

Subalpine grassland productivity increased with warmer and drier conditions, but not with higher N deposition, in an altitudinal transplantation experiment

Abstract. Multiple global change drivers affect plant productivity of grasslands and thus ecosystem services like forage production and the soil carbon sink. Subalpine grasslands seem particularly affected and may serve as a proxy for the cold, continental grasslands of the Northern Hemisphere. Here, we conducted a 4-year field experiment (AlpGrass) with 216 turf monoliths, subjected to three global change drivers: warming, moisture, and N deposition. Monoliths from six different subalpine pastures were transplanted to a common location with six climate scenario sites (CSs). CSs were located along an altitudinal gradient from 2360 to 1680 m a.s.l., representing an April–October mean temperature change of −1.4 to +3.0 ∘C, compared to CSreference with no temperature change and with climate conditions comparable to the sites of origin. To uncouple temperature effects along the altitudinal gradient from soil moisture and soil fertility effects, an irrigation treatment (+12 %–21 % of ambient precipitation) and an N-deposition treatment (+3 kg and +15 kg N ha−1 a−1) were applied in a factorial design, the latter simulating a fertilizing air pollution effect. Moderate warming led to increased productivity. Across the 4-year experimental period, the mean annual yield peaked at intermediate CSs (+43 % at +0.7 ∘C and +44 % at +1.8 ∘C), coinciding with ca. 50 % of days with less than 40 % soil moisture during the growing season. The yield increase was smaller at the lowest, warmest CS (+3.0 ∘C) but was still 12 % larger than at CSreference. These yield differences among CSs were well explained by differences in soil moisture and received thermal energy. Irrigation had a significant effect on yield (+16 %–19 %) in dry years, whereas atmospheric N deposition did not result in a significant yield response. We conclude that productivity of semi-natural, highly diverse subalpine grassland will increase in the near future. Despite increasingly limiting soil water content, plant growth will respond positively to up to +1.8 ∘C warming during the growing period, corresponding to +1.3 ∘C annual mean warming.

Effect of Potassium Source and Rate on Yield, Quality, and Tobacco-Specific Nitrosamines in Dark and Burley Tobacco

Field trials were conducted in Princeton, Murray, and Lexington, KY in 2016–2018 to determine response of dark and burley tobacco to potassium source (potassium sulfate or potassium chloride) and potassium rate (0, 93, 186, or 279 kg K ha−1). Field sites that showed higher potential for potassium yield response were selected based on low soil test potassium levels from soil samples collected in early spring each year. All potassium applications were made between 1 and 10 days before transplanting. Significant yield responses to potassium were seen in 5 of 12 trials at sites that had initial soil test potassium levels of ≤150 kg K ha−1. Although cured leaf chloride levels were >1% on average where potassium chloride was used, negative effects on cured leaf moisture were only seen in 1 of 12 trials, and negative effects on quality grade index were not seen in any trial. The most consistent effect of potassium chloride application seen in this research was a 28% reduction in average total tobacco-specific nitrosamines (TSNA) compared to potassium sulfate application. These results showing lower TSNA from potassium chloride applications, along with minimal effects on moisture and quality grade index, may cause the tobacco industry to reconsider the long-standing preference for potassium sulfate as the potassium source for tobacco production.

Effects of Mowing, Seeding Rate, and Foliar Fungicide on Soybean Sclerotinia Stem Rot and Yield

Sclerotinia stem rot (SSR or white mold), caused by Sclerotinia sclerotiorum (Lib.) DeBary, is an economically important fungal disease of soybean. SSR routinely causes yield loss in the upper Corn Belt of the United States due to wet, humid conditions that coincide with moderate temperatures. This study investigated the novel cultural practice of mechanical cutting, or mowing, as an SSR management practice across multiple seeding rates. Mowing soybean during early vegetative growth alters plant architecture and growth habit. This results in a microclimate within the canopy less suitable for disease development. Field trials were conducted in Iowa, Illinois, Michigan, and Wisconsin in 2017 and 2018. Experimental design was a randomized complete block with four replications. Treatments included mowing (mowing and no mowing), seeding rate (197,684, 271,816, and 345,947 seeds/ha), and fungicide application (boscalid, Endura, and no fungicide). Soybean was mowed at approximately the V4 (four unfolded trifoliate leaves) growth stage. Mowing reduced disease in multiple locations; however, it also reduced yield in most of the locations. In general, there was less SSR in plots with lower seeding rates. Fungicide significantly reduced SSR in two of the five site-years for which disease was observed. Significant yield response to fungicide was also observed in two of the nine total field trials. Results indicate cultural practices such as mowing and reduced seeding rate can decrease SSR severity but also can impact potential yield. Additionally, yield response to SSR management practices may not be observed if disease is absent or at low levels.

Foliar Micronutrient Application for High-Yield Maize

Nebraska soils are generally micronutrient sufficient. However, critical levels for current yields have not been validated. From 2013 to 2015, 26 on-farm paired comparison strip-trials were conducted across Nebraska to test the effect of foliar-applied micronutrients on maize (Zea mays L.) yield and foliar nutrient concentrations. Treatments were applied from V6 to V14 at sites with 10.9 to 16.4 Mg ha−1 yield. Soils ranged from silty clays to fine sands. Soil micronutrient availability and tissue concentrations were all above critical levels for deficiency. Significant grain yield increases were few. Micronutrient concentrations for leaf growth that occurred after foliar applications were increased 4 to 9 mg Zn kg−1 at 5 of 17 sites with application of 87 to 119 g Zn ha−1, 12 to 16 mg kg−1 Mn at 2 of 17 sites with application of 87 to 89 g Mn ha−1, and an average of 8.1 mg kg−1 Fe across 10 sites showing signs of Fe deficiency with application of 123 g foliar Fe ha−1. Foliar B concentration was not affected by B application. Increases in nutrient concentrations were not related to grain yield responses except for Mn (r = 0.54). The mean, significant grain yield response to 123 g foliar Fe ha−1 was 0.4 Mg ha−1 for the 10 sites with Fe deficiency symptoms. On average, maize yield response to foliar Fe application can be profitable if Fe deficiency symptoms are observed. Response to other foliar micronutrient applications is not likely to be profitable without solid evidence of a nutrient deficiency.

Response of wheat, pea, and canola to micronutrient fertilization on five contrasting prairie soils

A polyhouse study was conducted to evaluate the relative effectiveness of different micronutrient fertilizer formulation and application methods on wheat, pea and canola, as indicated by yield response and fate of micronutrients in contrasting mineral soils. The underlying factors controlling micronutrient bioavailability in a soil–plant system were examined using chemical and spectroscopic speciation techniques. Application of Cu significantly improved grain and straw biomass yields of wheat on two of the five soils (Ukalta and Sceptre), of which the Ukalta soil was critically Cu deficient according to soil extraction with DTPA. The deficiency problem was corrected by either soil or foliar application of Cu fertilizers. There were no significant yield responses of pea to Zn fertilization on any of the five soils. For canola, soil placement of boric acid was effective in correcting the deficiency problem in Whitefox soil, while foliar application was not. Soil extractable Cu, Zn, and B concentration in post-harvest soils were increased with soil placement of fertilizers, indicating that following crops in rotation could benefit from this application method. The chemical and XANES spectroscopic speciation indicates that carbonate associated is the dominant form of Cu and Zn in prairie soils, where chemisorption to carbonates is likely the major process that determines the fate of added Cu and Zn fertilizer.

Phosphate Fertilizer in Soybean-Wheat Cropping System Under No-Till Management

IImprovements in soybean (Glycine max [L.] Merrill) and wheat (Triticum aestivum L.) yields in cropping systems under no-till management (NTM) in the subtropics have been obtained through advances in phosphorus (P) utilization, cultivar selection, and planting and harvesting strategies. This fact, along with the P application in band application in consolidated planting, has resulted in lower P utilization efficiency and depleted soil P levels. The aim of this study was to evaluate the efficiency of P2O5 rates and application methods in soybean-wheat cropping under NTM during two growing seasons (2014–2016) in a Typic Eutrorthox. Four P2O5 rates (0, 30, 60, and 120 kg ha-1) of triple superphosphate (45% P2O5) were applied using two application methods (broadcast and band application at sowing) before the soybean and wheat crops were cultivated. Both P application methods resulted in a significant yield response to P2O5 rates for the soybean and wheat crops. Under NTM, broadcast P2O5 application was more effective than band application in soybean, and maximum grain yields were obtained with 129.3 and 88.1 kg P2O5 ha-1, respectively. Maximum wheat grain yields were obtained with 91.8 and 99.7 kg P2O5 ha-1 for broadcast and band application, respectively. Except for total P in leaves, nutrient uptake and yield components were not affected by the P application methods and rates. The results suggested that in soils with adequate available P levels of >15 mg kg-1 (Mehlich 1 extractant), the grain yield is equivalent or superior with broadcast P application as compared to band application for both soybean and wheat crops when cultivated in a Typical Eutrorthox under subtropical conditions. However, broadcast application is considered more effective for large areas of grain cultivation, where it is necessary to sow crops uniformly within the shortest possible time.

Effects of Leucaena biochar addition on crop productivity in degraded tropical soils

Biochar has the potential to increase crop yields on degraded, tropical soils. It can be readily produced in rural community settings using low-cost technology and is most economically feasible if produced from local biomass or waste residues. Biochar was produced from Leucaena biomass using low-cost pyrolysis and sequential pot experiments were then conducted in Malaysia on three degraded soils. We first evaluated the effect of Leucaena biochar on yields of Amaranthus, a leafy vegetable crop and measured changes to soil pH and nutrient availability over two growth cycles. We then tested whether any yield response to biochar was dependent upon the rate of biochar or fertilizer application. We found that biochar application at 30 t ha−1 with maximal fertilizer increased yields between 17 and 53% on very strongly acidic soil. Biochar added at 15 t ha−1 with maximal fertilizer increased yield by 54% on strongly acidic soil whilst there was no significant yield response on fertilized, slightly acidic soil. Unfertilized biochar treatments showed small yield responses across all soils over 2 growth cycles (9–11%), but yields were much lower than in fertilized treatments. Biochar also decreased short-term N availability when applied with fertilizers, which may improve nitrogen retention and substantially increased soil pH. This may reduce mobility of Fe, Mn and Al ions, which were negatively associated with yield. Our results suggest that Leucaena biochar can elicit a positive crop yield response but only when combined with fertilizer additions on very strongly to strongly acidic tropical soils.

Short- and Long-Term Effects of Lime and Gypsum Applications on Acid Soils in a Water-Limited Environment: 1. Grain Yield Response and Nutrient Concentration

Surface (0–10 cm) and subsoil (soil layers below 10 cm) acidity and resulting aluminum (Al) toxicity reduce crop grain yields. In South Western Australia (SWA), these constraints affect 14.2 million hectares or 53% of the agricultural area. Both lime (L, CaCO3) and gypsum (G, CaSO4) application can decrease the toxic effect of Al, leading to an increase in crop grain yields. Within the region, it is unclear if G alone or the combined use of L and G has a role in alleviating soil acidity in SWA, due to low sulfate S (SO4–S) sorption properties of the soil. We present results from three experiments located in the eastern wheatbelt of SWA, which examined the short-term (ST, 2 growing seasons), medium-term (MT, 3 growing seasons), and long-term (LT, 7 growing seasons over 10 years) effects of L and G on grain yield and plant nutrient concentrations. Despite the rapid leaching of SO4–S and no self-liming impact, it was profitable to apply G, due to the significant ST grain yield responses. The grain yield response to G developed even following relatively dry years, but declined over time due to SO4–S leaching. At the LT experimental site had received no previous L application, whereas, at the ST and MT sites, L had been applied by the grower over the previous 5–10 years. For the LT site, the most profitable treatment for wheat (Triticum aestivum L.) grain yield, was the combined application of 4 t L ha−1 with 2 t G ha−1. At this site, the 0–10 cm soil pHCaCl2 was 4.6, and AlCaCl2 was greater than 2.5 mg kg−1 in the 10–30 cm soil layer. In contrast, at the ST and MT sites, the pHCaCl2 of 0–10 cm soil layer was ≥5.5; it was only profitable to apply G to the MT site where the soil compaction constraint had been removed by deep ripping. The use of L increases soil pHCaCl2, resulting in the improved availability of anions, phosphorus (P) in the LT and molybdenum (Mo) at all sampling times, but reduced availability of cations zinc (Zn) in the LT and manganese (Mn) at all sampling. The application of G reduced Mo concentrations, due to the high SO4–S content of the soil.

Enhancement of the Productivity of Groundnut in Malawi through the Combined Use of Inoculants and Foliar Application of Nutrients

Low productivity characterizes the production of groundnut among smallholder farmers in Malawi. There is a need to explore options capable of increasing the productivity of the crop sustainably more especially under the changing climate. Against this background, experiments were conducted during the 2016/17 cropping season to investigate the potential to enhance the productivity of groundnut in Malawi through the combined use of inoculants (Graph-Ex and Histick-BASF) and foliar application of nutrients using Allwin fertilizer (legumes). The experiments were established at Bvumbwe and Chitala Agricultural research Stations and were laid in a randomized complete block design (RCBD) replicated four times. Data collected were analyzed in Genstat Discovery Edition 4 and were subjected to analysis of variance (ANOVA) at a 95% level of confidence. Means were separated by the least significant difference (LSD0.05). In general, foliar application of Allwin fertilizer alone particularly when conducted twice at two and four weeks after emergence produced a positive significant (p<0.05) groundnut grain yield response (97.8-170.8%) above the control. The yield increase is attributable to enhanced growth and development of the groundnut through the foliar supply of nutrients. In general, under the changing climate and amidst other constraints foliar feeding of nutrients using Allwin fertilizer alone particularly when conducted twice can increase significantly groundnut productivity in Malawi.

Sustainable intensification in Western Kenya: Who will benefit?

Sustainable Intensification (SI) is essential for Sub-Saharan Africa (SSA) to meet the food demand of the growing population under conditions of increasing land scarcity. However, access to artificial fertilizers is limited, and the current extension system is not effective in serving smallholder farmers. This paper studies farmers' response to improved fertilizer availability under field conditions. Data on farms and families were collected from 267 smallholder farms, while data on fertilizer use and crop response to fertilizer were collected on 127 farm plots. Fertilizer applications and maize yields were measured, and benefit to cost ratio (BCR) of fertilizer application was calculated and to assess its effect on food security. Farm household typologies were used to determine differences in farm endowment and food security classes. Fertilizer application did not significantly improve maize yields in 2017 due to unfavorable weather conditions and pest infestations, whereas significant yield responses were observed in 2018. Consequently, fertilizer application was economically beneficial (BCR >1) for only 45% of the farmers in 2017, compared to 94% in 2018 when 80% of the farmers passed the technology adaptation point (BCR > 2). Surprisingly, economic returns did not vary significantly between household types, implying that fertilizer application provides comparable benefits across all farm types. This is partly explained by the fact that soil fertility varied little between farm types (soil carbon content, for example, showed no correlation with farmer endowment). Still, large differences were observed in farmers' willingness to invest in larger fertilizer applications. Only a small proportion of farmers is expected to increase fertilizer applications as recommended. Our work demonstrates the need to address risks for smallholders and shows that socio-economic aspects are more important than biophysical constraints for policies promoting sustainable intensification.

Fertilizer Source and Rate Affect Sulfur Uptake and Yield Response in Corn

With sulfur deficiencies being found throughout Kansas, the evaluation of sulfur fertilization and plant uptake are vital to optimize corn production. The objective of this study was to evaluate the effect of application rates of sulfur on yield and uptake in corn. Nutrient concentrations in corn biomass and grain were evaluated at the Kansas River Valley Experiment Field at Rossville, KS, in 2019. Five treatments were evalu­ated, including a control with no sulfur and no nitrogen (N), and four fertilizer treat­ments with 180 lb of nitrogen and four rates of sulfur fertilizer (0, 30, 50, and 200 lb S/a). The nitrogen source was urea and balanced for all treatments at 180 lb N/a. The sulfur-containing fertilizer applications were at the time of planting corn. Whole corn plant biomass and grain samples were taken at physiological maturity and analyzed for nitrogen and sulfur concentrations. Results for the study show that sulfur application rates have a significant yield response in corn, likely contributing to increased uptake of nitrogen. Moreover, high yielding environments increased total plant sulfur uptake and removal.

Combined application of nitrogen and phosphorus to enhance nitrogen use efficiency and close the wheat yield gap on varying soils in semi‐arid conditions

AbstractA primary driver of the wheat yield gap in Australia and globally is the supply of nitrogen (N) and options to increase N use efficiency (NUE) are fundamental to closure of the yield gap. Co‐application of N with phosphorus (P) is suggested as an avenue to increase fertiliser NUE, and inputs of N and P fertiliser are key variable costs in low rainfall cereal crops. Within field variability in the response to nutrients due to soil and season offers a further opportunity to refine inputs for increased efficiency. The response of wheat to N fertiliser input (0, 10, 20, 40 and 80 kg N ha‐1) under four levels of P fertiliser (0, 5, 10 and 20 kg P ha−1) was measured on three key low rainfall cropping soils (dune, mid‐slope and swale) across a dune‐swale system in a low rainfall semi‐arid environment in South Australia, for three successive cropping seasons. Wheat on sandy soils produced significant and linear yield and protein responses across all three seasons, while wheat on a clay loam only produced a yield response in a high rainfall season. Responses to P fertiliser were measured on the sandy soils but more variable in nature and a consistent effect of increased P nutrition leading to increased NUE was not measured.

Copper fertilization in soybean–wheat intercropping under no–till management

The increase of soil organic matter (SOM) content under no–till (NT) management of field crops can reduce the availability of copper (Cu) in the soil. A field experiment was conducted during two growing seasons (2014–2015 and 2015–2016) with the objective of determining optimum Cu rates and critical Cu levels in soybean-wheat intercropping in a NT management. We used a randomized block design consisting of five Cu rates (0, 1, 2, 4, and 8 kg ha–1) applied before the first soybean crop. Both soybean and wheat showed a significant yield response to Cu, and the estimated value for maximum yield (EVMY) was 4.4 and 4.2 kg ha–1 Cu application for soybean and wheat, respectively. Wheat required available Cu levels of 15.5 (DTPA–TEA extractant) and 20.5 mg kg−1 (Mehlich 1 extractant) in the soil for maximum yield, whereas for soybean maximum yields were obtained with 7.7 and 14.1 mg kg–1, respectively, for the two extractants. For soybean, number of pods per plant (NPP) and Fe concentration in the grain were influenced by Cu rate, whereas in wheat Cu rate only affected plant height. Cu rates also had a positive effect on photosynthetic rate (A), intercellular CO2 level, transpiration rate, stomatal conductance, and chlorophyll content of soybean, and A and chlorophyll content in wheat. The results suggest the need to increase the amount of Cu applied to the soil in soybean-wheat intercropping in a NT management.

In sink-limited spring barley crops, light interception by green canopy does not need protection against foliar disease for the entire duration of grain filling

Disease management in cereals is heavily reliant on the use of fungicides, but development of anti-microbial resistance, effects on non-target organisms and persistence of active ingredients in the environment and food chain challenge the sustainability of this approach. Better targeting of fungicides according to crop need within an integrated pest management (IPM) programme could improve the sustainability of disease management. The objectives of the present study were to determine 1) the duration of protection of post-anthesis canopy light interception required to maximise the yield of spring barley and 2) to relate this to the response of crops to timing of fungicide applications. As the yield of spring barley is considered to be sink-limited (limited by the number and storage capacity of grains) rather than source-limited (limited by the amount of carbon assimilates available for grain filling) in many environments, we hypothesised that the canopy would not need to be protected for the entire grain filling period. Field experiments were conducted at two sites in the UK (Edinburgh and Herefordshire) over four years, providing contrasting climates and soil types. Shading was used to determine the response of grain filling to reductions in light interception over defined intervals, thereby mimicking effects of foliar disease on light interception, as shading is easier to control than the onset and duration of disease epidemics. Shades giving ˜67% reduction in photosynthetically active radiation (PAR) were erected over plots of disease-free crops at weekly intervals commencing at flowering and leaving them in place until harvest. The required duration of protection of light interception was estimated as the period from flowering to the time at which the onset of shading had no effect on yield. In a separate experiment the response to five fungicide timing treatments was determined on three relatively disease-susceptible varieties. Timings were the start of stem extension (referred to here as T1 only) and T1 followed by a second application at either flag leaf emergence (early T2), flowering (mid T2) or the start of rapid grain growth (late T2); untreated plots served as controls. Results showed that canopy PAR interception does not need to be protected for the entire grain filling period in order to maximise yield. The critical period determined from shading was 3–5 weeks after 50% ear emergence depending on the site year, or the first 72–90% of grain filling. There was a significant yield response to fungicide treatment in all site-years of 0.33−0.74 t ha−1 irrespective of the disease severity and yield potential of the site. Where disease severity was low to moderate a T1 application on its own gave sufficient protection during grain filling to maximise yield. Later applications increased healthy area PAR interception further, but effects occurred late during grain filling and did not increase yield. When disease was severe a T1 plus mid T2 application was required to protect PAR interception during the critical early to mid- grain filling period. These results provide the necessary physiological understanding to help target fungicide applications according to crop need.

Epidemics and Yield Losses due toCorynespora cassiicolaon Cotton

Target spot, caused by Corynespora cassiicola, has recently emerged as a problematic foliar disease of cotton. This pathogen causes premature defoliation during boll set and maturation that can subsequently impact yield, and on certain cotton cultivars loss can be substantial. This study sought to better understand target spot epidemics and disease-incited yield losses on cotton. In order to establish a range of disease, varying numbers of fungicide applications were made to each of two cotton cultivars in each of four site-years. Target spot intensity was rated over several dates beginning in late July or early August and continuing into September. Yield of seed plus lint (seed cotton) was recorded at harvest. When analyzed across cultivars, a second or third fungicide application increased yield compared with no treatment. Lack of significant yield response with a single fungicide application may have been due to timing of that application which preceded disease onset. The cultivar PhytoGen 499 WRF had consistently greater defoliation than any of the three Deltapine cultivars grown in each site-year. However, yields of both cultivars responded similarly to the fungicide regimes. Yield loss models based on late August defoliation were only predictive at site-years where conditions favored target spot development, i.e., abundant rain and moderate temperatures. Epidemic development fit the Gompertz growth model better than it did a logistic model. Knowledge of the underlying mathematical character of the epidemiology of target spot will prove useful for development of a predictive model for the disease.

Linking Nitrogen Losses With Crop Productivity in Maize Agroecosystems

To meet sustainable intensification goals in the US Midwest, strategies which maintain or increase yields while minimizing negative impacts on water quality are needed. In this study maize yield response and potential nitrogen (N) leaching losses were simultaneously quantified to test the hypothesis that N rates which produced maximum yields would result in minimum yield-scaled N leaching potential. Field experiments were conducted at two sites in 2015 and 2016 to determine the effect of N rate (0, 79, 179, 269 kg N ha-1) on yield, crop N uptake, potential N leaching losses, and post-harvest soil N concentrations. Results show that a significant yield response (up to 179 kg N ha-1) occurred in all years compared to the control. Nitrogen leaching potential increased at 269 kg N ha-1 compared to the control in 2015 but not 2016. Yield-scaled N leaching potential was not statistically different among treatments in three of four site-years. There was no improvement in crop N uptake or N recovery efficiency for 269 kg N ha-1 compared to 179 kg N ha-1 in three of four site-years, which coincided with a trend of increasing post-harvest soil N concentrations, further escalating the risk of environmental N losses. These results did not support our hypothesis that yield-scaled N leaching potential is minimized at N rates that optimize yields (on a normalized basis yield-scaled N leaching potential increased by 28% compared to the control). However, normalized data indicate that 179 kg N ha-1, the N rate most closely aligned with current recommendations in this region, resulted in 96% of maximum yield while preventing a 25% increase in yield-scaled N leaching potential compared to 269 kg N ha-1, underscoring the potential for achieving high yields while avoiding increased N leaching potential on an environmental efficiency basis.

Low Benefits from Fungicide Use on Hard Red Wheat in Low-Disease Environments

The use of fungicides on hard red wheat in the northern Great Plains increased in part owing to inexpensive fungicide options and several years of foliar disease epidemics. In some instances, fungicides are used in the absence of disease, prompting questions on the perceived value of these applications. This study analyzed yield data from 46 fungicide trials conducted in low-disease environments from 2007 to 2014 on hard red spring wheat and hard red winter wheat. Data were sorted and organized to determine yield response attributed to fungicide application timing (Feekes 2–3 or Feekes 9) and fungicide mode of action. Fungicide modes of action included quinone outside inhibitors (QoIs), demethylation inhibitors (DMIs), succinate dehydrogenase inhibitors (SDHIs), and blends (mixtures of QoI, DMI, or SDHI). A meta-analysis indicated a significant yield response of 101.6 kg/ha for a Feekes 9 application and 69.3 kg/ha for applications that used a QoI. Economic analyses indicated that when a midpoint value for both wheat price and application cost were used, less than one-third of the trials had a profitable net return when a Feekes 9 application was used. The infrequent positive yield responses associated with foliar fungicides in low-disease environments should prompt growers to evaluate disease risk prior to making an application for foliar diseases.

Sugarcane Yield Response to Potassium Fertilization as Related to Extractable Soil Potassium on Florida Histosols

Core Ideas Sugarcane yield responses to K fertilizer were attributable to increases in sugarcane biomass. There was reduced sucrose concentration at higher K rates in 4 of 14 crop years. Maximum K fertilizer requirement determined was 27% less than current recommendation. Soil test K limit for K fertilizer application was within 12% of the current limit. Sugarcane (Saccharum spp.) has a large K requirement and so K fertilizer can be a major cost for growers. Histosols in the Everglades Agricultural Area (EAA) of Florida are shallower with higher pH than when current sugarcane K fertilizer recommendations were established in the 1970s. This study was conducted to determine sugarcane yield response to K fertilizer as related to extractable soil K on Florida Histosols. Six small‐plot (83, 120, or 138 m2) field experiments were established as randomized complete block (RCB) designs (four or six replications) with annual K rates ranging from 0 to 279 kg K ha−1. There were significant sugarcane and sucrose yield responses to K fertilizer and these were attributable to increases in sugarcane biomass. There was evidence of reduced sucrose concentration at higher K rates in 4 of 14 crop years. Orthogonal contrasts determined significant sucrose yield response to K fertilizer compared to the zero rate in 5 of 14 crop years. Nonlinear regression determined that the acetic acid‐extractable soil K value at or above which K fertilization is not required was within 12% of the current value. Maximum K fertilizer requirement determined in the study was 170 kg K ha−1 at an acetic acid‐extractable K value of 20 g K m−3, which is 27% less than the current recommendation. Results of a previously unpublished K rate trial confirmed the results of the current study, which will be used to update K fertilizer recommendations on Florida Histosols.

Phosphorus Over-Fertilization and Nutrient Misbalance of Irrigated Tomato Crops in Brazil.

Over the past 20 years, the use of center-pivot irrigation has increased tomato (Solanum lycopersicum L.) yields in Brazil from 42 Mg ha−1 to more than 80 Mg ha−1. In the absence of field trials to support fertilizer recommendations, substantial amounts of phosphorus (P) have been applied to crops. Additional P dosing has been based on an equilibrated nutrient P budget adjusted for low-P fertilizer-use efficiency in high-P fixing tropical soils. To document nutrient requirements and prevent over-fertilization, tissue samples and crop yield data can be acquired through crop surveys and fertilizer trials. Nevertheless, most tissue diagnostic methods pose numerical difficulties that can be avoided by using the nutrient balance concept. The objectives of this study were to model the response of irrigated tomato crops to P fertilization in low- and high-P soils and to provide tissue diagnostic models for high crop yield. Three P trials, arranged in a randomized block design with six P treatments (0–437 kg P ha−1) and three or four replications, were established on a low-P soil in 2013 and high-P soils in 2013 and 2014, totaling 66 plots in all. Together with crop yield data, 65 tissue samples were collected from tomato farms. We found no significant yield response to P fertilization, despite large differences in soil-test P (coefficient of variation, 24%). High- and low-yield classes (cutoff: 91 Mg fruits ha−1) were classified by balance models with 78–81% accuracy using logit and Cate–Nelson partitioning models. The critical Mahalanobis distance for the partition was 5.31. Tomato yields were apparently not limited by P but were limited by calcium. There was no evidence that P fertilization should differ between center-pivot-irrigated and rain-fed crops. Use of the P budget method to arrive at the P requirement for tomato crops proved to be fallacious, as several nutrients should be rebalanced in Brazilian tomato cropping systems.