Current Fertilizer Recommendations Research Articles

Determining the Best Rate of Blended NPKSZnB Fertilizer for Optimum Onion Yield and Yield Components in Northwestern Tigray, Ethiopia

Aim: The nutrient content of current fertilizer recommendations is unbalanced and is based on a very general and blanket recommendation for all soil and crop types, and their economic benefit is low. Therefore, this study was initiated to validate the recommendations regarding blended fertilizers applied to the soil and to identify the best fertilizer dose that ensures optimal yield and maximum economic return. Study Hypotheses: significance effect of blended NPKSZnB fertilizer on onion yield and yield components. Study Design: The experiment was designed using a randomized complete block design with three replications and seven treatments. Place and Duration of the study: The field experiment was conducted in the off-season of 2018 and 2019 in Tahtay Koraro (two farmers), and Laelay adyabo (two farmers) districts of in northern Ethiopia. Methodology: Seven treatments with NPKSZnB fertilizer rates (25, 50, 100, 150, 200, 250 and 300 kg·ha-1) were tested under irrigation conditions. Thus, for each plot nitrogen from Urea was applied at a rate of 150 kg ha-1. Surface soil samples were collected before planting onion harvesting at a depth of 0-20 cm to analyze selected soil chemical properties such as pH, extractable electric conductivity (ECe), cation exchange capacity (CEC), total nitrogen (TN), available P and exchangeable bases (K, Mg, Ca, and Na). Results: The application of different doses of NPKSZnB under irrigation conditions had a statistically significant (P < 0.05) impact on onion phenology, yield and yield components. The highest average onion yield (10,329 and 19,196 kg ha-1) was obtained after applying compound fertilizer doses of 200 and 250 kg ha-1 in Teahtay Koraro and Laelay Adyabo districts, respectively. However, the use of NPKSZnB fertilizer at a dose of 100 and 50 kg ha-1 for onion cultivation under irrigated conditions in T/koraro and L/adyabo districts was found to be economically viable. Thus, growers in both districts should use NPKSZnB compound fertilizer at these rates for onion production and productivity. Conclusion: Therefore, farmers in both districts should use NPKSZnB compound fertilizer at these rates for optimum onion production.

Using Mathematical Models to Study the Influences of Different Ratios of Chemical Nitrogen, Phosphorus, and Potassium on the Content of Soluble Protein, Vitamin C, and Soluble Sugar in Melon.

The current fertilizer recommendations for melon plantation have many limitations and exhibit deficiencies regarding future development. Therefore, in this study, the optimal quantities of fertilizer, in terms of the effects of single factors and interaction effects, are studied. There were significant interaction effects between N and P, N and K, P and K; the contents of soluble protein, vitamin C (Vc), and soluble sugar in melon could be improved using the optimal fertilization ratios. The optimal ratio of N:P:K was 2.33:1:3.85, with the amounts of N, P2O5, and K2O, respectively, being 157.5, 67.58, and 260.38 kg/hm2, yielding 8.73 g/kg of soluble protein in melon. The optimal ratio of N:P:K was 2.03:1:3.36, with amounts of N, P2O5, and K2O being 157.50, 77.40, and 260.38 kg/hm2, respectively, yielding 25.32 g/kg Vc content in melon. Finally, the optimal ratio of N:P:K was 1.53:1:3.36, with the amounts of N, P2O5, and K2O being 118.07, 77.40, respectively, and 260.38 kg/hm2, yielding 13.34% soluble sugar content in melon.

Modification of Nutrient Requirements for a Four Crop-Based Cropping System to Increase System Productivity, Maintain Soil Fertility, and Achieve Sustainable Intensification

Sustainable and resilient cropping intensity is now a global focus to address the food demand and nutrition security of the growing population. For sustainable intensification, maintaining soil fertility is a key concern. The nutrient management for the recently developed four crop-based cropping system in Bangladesh has not yet been studied. Hence, field experiments were conducted on the nutrient management of the four crop-based cropping system [Aus (pre-monsoon rice), Aman (monsoon rice), lentil, and mungbean] in calcareous soil in Bangladesh during the years of 2016/17 and 2017/18 to determine the appropriate fertilizer management package to improve crop productivity and sustain soil fertility. The experiment had six treatments assigned in a randomized complete block design with three replications. The treatments included T1 = control (without synthetic fertilizer), T2 = 50% recommended dose of fertilizer (RDF), T3 = 75% RDF, T4 = 100% RDF, T5 = 125% RDF, and T6 = farmers’ practice (FP). The results revealed that the 125% RDF significantly contributed to higher yields of all four crops. The rice equivalent yield (REY) was the highest for the fertilizer management of 125% RDF, which was 45.5%, 9.4%, and 12.2% higher than the control (T1), 100% RDF (T4), and FP, respectively. Considering the uptake of nutrients (N, P, K, S, Zn, and B) by the crops in the cropping system, the 125% RDF was superior to the other treatments. The nutrient management practices had a positive influence on the apparent nutrient recovery (ANR) efficiency of the cropping system. The fertilizer management of 125% RDF was also economically more profitable due to the increment in the cost–benefit ratio of 26.8%, 4.4%, and 4.9% over the control, 100% RDF, and FP, respectively. The results indicate that the current fertilizer recommendations and FP for aus, aman, lentil, and mungbean are not adequate for the change from the three crop to the four crop-based pattern, and an increased dose of fertilizer is required to increase the yield of each individual crop as well as the total system’s productivity. The fertilizer use efficiency is also higher for 125% RDF than the 100% RDF and FP indicating that to sustain the soil fertility in the four crop-based system, the current RDF and FP are not sufficient. This finding will help intensive cropping areas in preventing nutrient deficiencies that would lead to a reduction in the crop yield.

English

The potato is one of the most important food and cash crops in Malawi, but current yields are low and the fertilizer recommendations rely on outdated soil fertility information. To understand the influence of soil factors in limiting current potato production, the mineralogical and physicochemical soil characteristics of 26 farms in the central highlands of Malawi were evaluated. Cluster analysis with clay, crystalline iron oxide, and total carbon content revealed three clusters with two corresponding to Ferralsols and one to Regosols, which are known to exist in the area. In the three clusters, the soil was generally acidic with low exchangeable acidity and aluminium (Al; < 0.7 cmolc kg-1); thus, Al toxicity was not a concern because the soil solution Al would be very low to negatively affect plant growth. Inorganic nitrogen was adequate, while available phosphate and exchangeable potassium (K) were variable within each cluster. However, a deficiency in exchangeable calcium (Ca; < 3.6 cmolc kg-1) and magnesium (Mg; < 1.2 cmolc kg-1) indicated that low base cation concentration was the problem and the potential yield-limiting factor. Soil management, not soil type, appeared to determine soil nutrient conditions based on the current soil Ca and Mg deficiencies and variable K nutrient status. There is a need for updating the current fertilizer recommendations by incorporating K, Ca, and Mg and promoting soil amendment interventions using locally available animal manure and plant ash. Key words: acid soil; fertilizer; Ferralsols, Regosols, Solanum tuberosum L., aluminium toxicity, calcium; magnesium.

Plant Growth and Physiological Responses to Improved Irrigation and Fertilization Management for Young Peach Trees in the Southeastern United States

New peach orchards in the southeastern United States are often not irrigated until 3 or 4 years after planting. During those years, the only water comes from rainfall. Droughts in the region are becoming more common, making irrigation more important. At the same time, fertilization practices follow recommendations developed decades ago and may not be optimal for current production practices. This research aimed to investigate the effect of different irrigation and fertilization practices on young ‘Julyprince’ trees grafted onto ‘Guardian™’ rootstock. The treatments consisted of irrigated vs. nonirrigated trees, drip- vs. microsprinkler-irrigated trees, and four different fertilizer levels (25%, 50%, 100%, and 200%; with 100% = current fertilizer recommendations). Responses to the treatments varied by year. In 2016, below-average rainfall (severe drought as classified by the U.S. Drought Monitor) was recorded throughout the year. This severe drought reduced the growth of nonirrigated trees compared with irrigated trees (average reductions of 56% in canopy volume, 39% in trunk cross-sectional area, 39% in leaf and stem water potential, and 40% in leaf photosynthesis). The adverse effects on tree growth and physiological responses of the 2016 season carried over to 2017, which was characterized by a short period of below-average rainfall in early spring. Nonirrigated trees displayed advanced budbreak progression; reduced commercial yield (10.9 vs. 13.4 kg/tree for nonirrigated vs. irrigated trees); and smaller trunk cross-sectional area (54.0 vs. 70.1 cm2) and canopy volume (8.9 vs. 10.9 m3) compared with irrigated trees. In 2018, rainfall was like the historical average throughout the year. Major differences continued to be trunk cross-sectional area (103.4 vs. 126.7 cm2) and canopy volume (15.8 vs. 17.8 m3), with nonirrigated trees being smaller than irrigated trees. No major or consistent differences were found between drip vs. microsprinkler irrigation or among fertilizer levels during the 3 years of the experiment. During the first years of orchard establishments, irrigation resulted in increased plant growth, commercial yield, and superior water status (higher values of water potential) compared with no irrigation, especially when rainfall was below the historical average. Although no major differences were found between the irrigation systems, drip irrigation used 35% less water than microsprinkler irrigation. While different fertilizer levels did not induce major differences in young trees’ growth and yield, potential economic savings and long-term effects of reduced fertilizer applications are being monitored as trees mature.

Geospatial distribution of soil organic carbon and soil pH within the cocoa agroecological zones of Ghana

Geospatial distribution of soil organic carbon (SOC) and soil pH is an important component of soil fertility management in sustainable cocoa (Theobroma cacao L.) production. Spatial precision of cocoa soil fertility management in Ghana is rare due to paucity of spatially precise knowledge of farm soil properties. This study sought to provide spatially explicit knowledge of the underlying trends of SOC and pH in and across cocoa agroecological zones, covering 61 cocoa districts in Ghana. Soil samples collected at 20 cm depth from 739 newly established cocoa farms were analyzed using classical and geospatial statistical methods. We described the spatial pattern (clustering) of SOC and pH and predicted their spatial continuity from observed and unobserved locations. Results generally revealed unsuitably low SOC (0.39 ± 0.009 g/100 g) and strong acidity (5.35 ± 0.027). Univariately, SOC varied more continuously (58%) over a longer distance (1.424 km) than pH, which varied moderately around 55.7% over a shorter distance (0.598 km). Covariates improved the co-regionalized structure and homogeneity of the predictions. Thus, the spatial dependencies of SOC and pH were moderate but the risk of imprecision was higher for SOC than pH. This knowledge is crucial in our understanding of the geo-physicochemical phenomena controlling the spatial distribution of SOC and pH in the cocoa farms and districts across the agroecological zones. The findings underscored dwindling SOC and pH in line with historic boom-bust cycle of cocoa production hot and cold spots transitions. The findings are also indicative of the adverse implications of relying on current blanket fertilizer recommendations. Therefore, a change from the current agronomic practice of fertilizer use to one that recognizes the SOC and pH needs of specific areas, farms and cluster of districts is recommended.

Science-based decision support for formulating crop fertilizer recommendations in sub-Saharan Africa

In sub-Saharan Africa, there is considerable spatial and temporal variability in relations between nutrient application and crop yield, due to varying inherent soil nutrients supply, soil moisture, crop management and germplasm. This variability affects fertilizer use efficiency and crop productivity. Therefore, development of decision systems that support formulation and delivery of site-specific fertilizer recommendations is important for increased crop yield and environmental protection. Nutrient Expert (NE) is a computer-based decision support system, which enables extension advisers to generate field- or area-specific fertilizer recommendations based on yield response to fertilizer and nutrient use efficiency. We calibrated NE for major maize agroecological zones in Nigeria, Ethiopia and Tanzania, with data generated from 735 on-farm nutrient omission trials conducted between 2015 and 2017. Between 2016 and 2018, 368 NE performance trials were conducted across the three countries in which recommendations generated with NE were evaluated relative to soil-test based recommendations, the current blanket fertilizer recommendations and a control with no fertilizer applied. Although maize yield response to fertilizer differed with geographic location; on average, maize yield response to nitrogen (N), phosphorus (P) and potassium (K) were respectively 2.4, 1.6 and 0.2 t ha−1 in Nigeria, 2.3, 0.9 and 0.2 t ha−1 in Ethiopia, and 1.5, 0.8 and 0.2 t ha−1 in Tanzania. Secondary and micronutrients increased maize yield only in specific areas in each country. Agronomic use efficiencies of N were 18, 22 and 13 kg grain kg−1 N, on average, in Nigeria, Ethiopia and Tanzania, respectively. In Nigeria, NE recommended lower amounts of P by 9 and 11 kg ha−1 and K by 24 and 38 kg ha−1 than soil-test based and regional fertilizer recommendations, respectively. Yet maize yield (4 t ha−1) was similar among the three methods. Agronomic use efficiencies of P and K (300 and 250 kg kg−1, respectively) were higher with NE than with the blanket recommendation (150 and 70 kg kg−1). In Ethiopia, NE and soil-test based respectively recommended lower amounts of P by 8 and 19 kg ha−1 than the blanket recommendations, but maize yield (6 t ha−1) was similar among the three methods. Overall, fertilizer recommendations generated with NE maintained high maize yield, but at a lower fertilizer input cost than conventional methods. NE was effective as a simple and cost-effective decision support tool for fine-tuning fertilizer recommendations to farm-specific conditions and offers an alternative to soil testing, which is hardly available to most smallholder farmers.

Predicting Cool‐Season Turfgrass Response with Solvita Soil Tests, Part 2: CO2–Burst Carbon Concentrations

Current turfgrass fertilizer recommendations do not account for plant‐available soil N mineralized from labile C fractions. The Solvita Soil CO2–Burst (SSCB) test can measure mineralizable C via soil CO2 respiration. This study was conducted across 3 yr (2014–2016) in Connecticut to determine: (i) if SSCB–C concentrations are correlated to responses from predominately Kentucky bluegrass (Poa pratensis L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] lawns, and (ii) the probability of turfgrass responses being equal to or greater than responses from common urea rates in relation to SSCB–C concentrations. Randomized complete block design field experiments were set out with 23 rates of organic fertilizer (0–2000 kg N ha−1 yr−1) and four different rates of urea (50, 100, 150, and 200 kg N ha−1 yr−1). Yearly spring soil samples were analyzed for SSCB–C concentrations and correlated with turfgrass responses. Growth and quality responded positively and linearly (P < 0.001) to SSCB–C concentrations, but variability was high and correlations were relatively weak. When spring soil SSCB–C concentrations were ≥91, 113, 166, and 211 mg kg−1, there was a ≥90% probability that overall combined responses across species and variables would be equal to or greater than responses obtained from urea rates of 50, 100, 150, and 200 kg N ha−1 yr−1, respectively. The SSCB test has promise for predicting the probability of soils supporting turfgrass whose performance equals or exceeds benchmark values. This would be helpful in guiding N fertilization, but high variability within the test may limit its predictive ability.

Soil Fertility Status in Relation to Farmers’ Practices Under Maize Based Systems in Western Region of Kenya: Yield Gap Analysis

A study was carried out in Kenya Cereal Enhancement Project site in Western region of Kenya to examine the soil fertility status in relation to the current blanket fertilizer recommendations and farmers’ practices across the four wards, namely: Motosiet, Keiyo, Cherangani and Kwanza. The baseline fertility status in different soil mapping units was assessed in terms of soil productivity index with a view of analyzing the levels of nutrients and yield gaps. Using the standard soil survey procedures, six soil mapping units were identified as UUr1, UUr2, UUr3, RUd, RUrb, and BU1.. The results showed that the highest productivity index was in unit BU1, followed by UUr1, UUr2, UUr3, and RUrb with values of 40.5, 29.4, 25.0, 16.0 and 8.9% respectively. Keiyo Ward had the highest level of nitrogen, being 125.82, followed by Motosiet, Cherangani and Kwanza with values of 99.92, 97.12, and 81.12 kg/ha respectively. Phosphorous level was highest in Kwanza (136.41 kg/ha), followed by Cherangani (106.82 kg/ha) and Keiyo Ward (76.08 kg/ha). The lowest level was recorded in Motosiet with the value of 72.56 kg/ha. Potassium was found to be adequate in all the four Wards with values ranging between 347.67 and 410.34 kg/ha. The maximum maize production recorded in the project sites was 9,000 kg/ha, with a yield gap of 1,000 kg/ha. This was achieved through application of 100 and 50 kg/ha of DAP and CAN respectively. This was followed by 6,750 kg/ha obtained through application of 50 kg/ha of DAP and CAN. The yields from the rest of the sites ranged between 1,800 and 4,500 kg/ha with yield gaps varying from 3,250 to 8,650 kg/ha. The lowest yields were obtained in Keiyo, followed by Kwanza Ward despite the relatively high macro- nutrient levels in the soils of the two Wards. This was attributed to soil-related constraints caused by the increased soil structural degradation and loss of soil tilth. Therefore, it is recommended that the envisaged climate smart technologies be geared towards enhancement of nutrient and water use efficiency through improved soil structure and tilth.

Fertilizer Program Impacts Yield and Blossom End Rot in Bell Pepper

High-value vegetable crops such as bell pepper (Capsicum annuum) are heavily fertilized by growers who seek to maximize yields. Field experiments were conducted in Spring 2016 and 2017 evaluating two liquid fertilizers with and without calcium (Ca), applied at three nitrogen (N) and potassium (K) levels in two varieties of bell pepper to determine whether current fertilizer recommendations were adequate and whether fertilizer source impacted fruit yield and quality. Plants were grown using plastic mulch and drip irrigation following standard production practices for the region. Two liquid fertilizer programs [7N–0P–5.8 (7–0–7) and 4N–0P–6.6K/9N–0P–0K–11Ca (4–0–8/CN9)] were applied twice weekly at three N rates (175, 200, and 225 lb/acre N). Yield, cull rate, and foliar nutrient concentrations were measured. In 2016, total marketable yields were greatest [910 boxes/acre (28 lb/box)] and blossom end rot (BER) incidence (14.4%) lowest in plants grown with the supplemental Ca (4–0–8/C9 fertilizer) at 175 lb/acre N. Cull rates increased in plants grown without supplemental Ca during the season (7–0–7 fertilizer), with BER incidence ranging from 22.9% to 27.2%. Yields ranged from 590 to 740 boxes/acre in plants grown without supplemental Ca in 2016. In 2017, yields ranged from 530 to 790 boxes/acre in plants grown with supplemental Ca at 200 and 175 lb/acre N, respectively. Culls due to BER were lower in 2017 than in 2016. In 2016, BER incidence was greater in ‘PSO9979325’ compared with ‘Antebellum’, despite no differences in total yield. Foliar nutrient levels were largely unaffected by fertilizer program; however, foliar N and K concentrations increased with the rate of N and K fertilization. The results of this study suggest that using liquid fertilizer program containing some Ca may benefit bell pepper growers in some, but not all, growing seasons.

Nitrogen Fertilizer Optimization for Sugarbeet in the Red River Valley of North Dakota and Minnesota

Single fertilizer nitrogen rate of 146 kg N ha−1 for sugarbeet is outdated. Sugarbeet–fertilizer nitrogen recommendation should consider soil characteristics. Sugarbeet yield and sugar content was optimized at 112 kg N ha−1. In‐season soil nitrogen and red‐edge normalized difference vegetative index can predict yield response to nitrogen. Economic optimum nitrogen rate varies from 0 to 405 kg N ha−1. Fertilizer N application is critical to optimize sugarbeet (Beta vulgaris L.) yield and sugar concentration. Regardless of observed yields, current fertilizer recommendations in North Dakota and Minnesota suggest a single application rate of 146 kg N ha−1 (considering both fertilizer N residual soil N of 120 cm depth) for the Red River Valley (RRV) irrespective of soil type and organic matter content. Field experiments were conducted at three sites to determine sugarbeet response to N application rates, 0, 112, 146, 179, and 213 kg N ha−1 and optimal N rate during 2015 and 2016 growing seasons. Year and site had a significant effect on yield and sugar concentration. In 2015, fertilizer‐N significantly increased yield for all three sites, but in 2016, only one site responded to N. The highest N rate (213 kg N ha−1) reduced sugar concentration in 2016. In‐season soil available N (of 0–120 cm) significantly correlated with yield (R2 = 0.35) and economic return (R2 = 0.28). In season, red edge normalized difference vegetative index (RENDVI) based on the handheld optical sensor was significantly (P < 0.05) related to fertilizer‐N application rate. Economic optimum N rate for three sites varied from 0 to 405 kg N ha−1 depending on year and site characteristics. Our results suggest a revision of current sugarbeet fertilizer N recommendation to replace the single rate with N rates based on site characteristics and profitability to N applications.

Lake Erie, phosphorus, and microcystin: Is it really the farmer's fault?

The size of the harmful algal blooms in western Lake Erie is strongly correlated with agricultural phosphorus (P) loading from tributaries. Despite farmers9 efforts to reduce sediment-bound P loadings and fertilize using current guidance, the media and public have singled them out as the culprit in Lake Erie re-eutrophication. In this paper, two farmer surveys were used to evaluate if farmers in the Lake Erie region follow P fertilizer recommendations, and we also review historic and current P management guidance provided by the scientific community and agricultural industry. The majority (56% to 80%) of farmers apply P fertilizers at or below the current fertility recommendations. Wholesale agronomic changes (e.g., no-tillage adoption, crop cultivar advances, and fertilizer application and formulation) have occurred since current fertilizer recommendations were developed. Although crop P uptake mechanisms have not changed, these agronomic changes have altered P cycling in soil and water. Based on these results, it is time that the scientific community and agricultural industry acknowledge that our current guidance may be contributing to eutrophication. We must ask whether or not we have (1) developed appropriate fertility guidance, (2) developed and recommended appropriate practices to protect water quality, (3) adequately considered “the law of unintended consequences” in conservation recommendations, and (4) focused too much on short-term economic outcomes while disregarding environmental quality. Improved understanding, reconsideration of traditional recommendations, and wider farmer adoption of the most effective practices are needed to develop a sustainable agricultural system in the Western Lake Erie Basin that produces needed commodities while preserving ecosystem integrity.

Why organic resources and current fertilizer formulations in Southern Africa cannot sustain maize productivity: Evidence from a long-term experiment in Zimbabwe

Sustainability of maize-based cropping systems is a major challenge for southern Africa, yet the demand for maize as staple food and animal feed in the region continues to increase. A study was conducted on a sandy clay loam (220 g clay kg-1 soil) at Domboshawa in Zimbabwe to investigate the long-term effects of organic resource quality and application rate, and nitrogen (N) fertilization on soil chemical properties and maize (Zea mays L.) productivity. Crotalaria juncea (high quality), Calliandra calothyrsus (medium quality), cattle manure (variable quality), maize stover and Pinus patula sawdust (both low quality) were incorporated into soil at 4.0 t C ha-1 (high rate) and 1.2 t C ha-1 (low rate) at the start of each cropping season for nine consecutive years. At both high and low application rates, each of the five organic resources was applied in combination with or without mineral nitrogen (N) fertilizer at 120 kg N ha-1. The nine-year period saw maize grain yields declining by 22% to 84% across treatments despite increases in soil organic carbon, total N and available P from 6% to 80%. Crotalaria, Calliandra and manure led to a less steep yield decline. Exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and soil pH explained much of the variation in yield patterns observed under the different organic resource applications. Maize grain yield was positively correlated with exchangeable Ca (r = 0.51), Mg (r = 0.62) and K (r = 0.53), and soil pH (r = 0.49), but negatively correlated with other soil properties over the 9-year period. We concluded that declining soil exchangeable basic cations were the underlying causes of decreasing maize productivity, and was aggravated by use of low rates of organic resource inputs, particularly with N fertilization. Current nutrient management and fertilizer recommendations that emphasize inorganic N, P and K significantly undervalue the role played by organic resources in sustainability of maize cropping systems in southern Africa.

Effectiveness of Current Fertilizer Recommendations for Irrigated Rice in Integrated Crop-Livestock Systems

ABSTRACT: Irrigated rice in the state of Rio Grande do Sul (Brazil) has shown significant growth in yield in recent years due to improved management practices, especially in regard to fertilizer use. However, the response curves that led to the current fertilizer recommendations do not consider integrated systems prevailing in rice-producing regions that have adopted the practice of integrated crop-livestock systems. The aim of the present study was to evaluate the effectiveness of current fertilizer recommendations for irrigated rice in [...]

Ammonia volatilization from frequently applied fertilizers for the low-country tea growing soils of Sri Lanka

Ammonia volatilization is one of the major nitrogen loosing pathways in agricultural fields. Particularly, Low-country tea growing areas of Sri Lanka having warm humid climate, often records low or poor responses to current fertilizer recommendations. Therefore, a glasshouse experiment was conducted to determine the gravity of ammonia volatilized from four major tea growing Soil Series of the Low-country wet zone. Air tightened closed chambers with soils containing acid traps were used to quantify ammonia volatilized from applied fertilizers. The experiment was conducted for 100 days while monitoring temperature and relative humidity in the glasshouse which were comparable with prevailing conditions in the low-country wet zone. Volatilized ammonia was quantified daily at the beginning and later with elapsed time. Curves defining the release of ammonia with time and the change of pH with time were plotted from the results. Significant differences were observed in soil pH changes among treatments. Sulphate of ammonia based T1130 mixture recorded the least change in soil pH while urea based VPLC 880 showed the highest variation. During the experimental period, highest pH was recorded at the fourth day after treatment application which confirms the peak hydrolysis of urea. No significant differences were recorded in soil pH changes with soil series. Ammonia volatilization was lowest in T 1130 treatment and it behaved similar to the control treatment without fertilization. Ammonia losses were highest in VPLC 880 fertilizer amounting to 29%. Other urea based mixtures also showed considerably higher losses as U 709 – 27%, U834 – 27%, UT 752 – 26%. T 1130 showed minimum losses as 1% similar to the control. Among soil Series NH3 losses sequenced as Dodangoda > Weddagala > Malaboda > Pallegoda. As these soils show lower pH buffering ability, split application of urea based fertilizers may effective to minimize said NH3 losses. Tropical Agricultural Research Vol. 26 (1): 48– 61 (2014)

Fertilization of Landscape Palms to Reduce Nitrogen and Phosphate Impacts on the Environment

Palms are an increasingly important element in landscapes in the subtropical and warm temperate regions of the United States. Unfortunately, palms have very high nutritional requirements and rarely can be found without at least one nutrient deficiency, especially on the sandy and calcareous soils of the southeastern United States. These deficiencies are conspicuous and unsightly, reduce canopy size and vigor, and can become fatal. Current maintenance fertilizer recommendations for landscape palms in Florida growing in these soils entail four applications per year of an 8N–0.9P–10K–4Mg plus micronutrients palm fertilizer. However, because phosphorus (P) and nitrogen (N) are considered pollutants of ground and inland and coastal surface waters, it is important to apply only as much of these elements as necessary for palm health. This study showed that areca palms (Dypsis lutescens) can be grown in a native sand soil or in a calcareous fill soil without supplemental P and with no N applied during the rainy summer months of June through September when application of these elements may be legally restricted. It also demonstrated that the negative effects caused by high N:potassium (K) ratio turf fertilizers can be mitigated by adding a controlled release palm fertilizer that contains no N or P. Because of strong dilution effects in this study, leaf nutrient concentrations were found to be poor indicators of palm quality and nutritional status.

Effects of long-term chemical fertilization on trends of rice yield and nutrient use efficiency under double rice cultivation in subtropical China

A long-term (33 years) experiments were conducted to investigate the effect of chemical fertilization on rice yield, yield trends, soil properties, agronomic efficiency of applied nutrients and nutrient balance for the double rice cropping systems in subtropical China. The treatments were different combinations of N, P and K fertilizers (N, NP, NK and NPK), double dose of recommended NPK (2NPK) and no fertilizer control (control). Compared with no fertilizer control, all fertilization treatments had no significant effects on soil pH and SOC contents (P > 0.05), but generally increased nutrients content when corresponding elements were applied. The impact of fertilizers on grain yields was 2NPK > NPK > NP > NK > N, and application of P fertilizer not only increased the rice yield, but improved yield stability. The trend of agronomic use efficiency of applied P was significantly positive (P < 0.05) only for the first rice crop, suggesting that P fertilizer played a less important role in the second rice season than in the first rice season. The study indicated that the current local fertilizer recommendations should be optimized for the consideration of differences in indigenous nutrient supplies in different rice seasons.

Fertilizer Composition, Concentration, and Irrigation Method Affect Growth and Development of Oxalis regnellii and O. triangularis

Oxalis regnellii, the shamrock plant, and O. triangularis are niche ornamental greenhouse crops produced and marketed primarily for their foliage; thus, it is imperative to produce the fullest, most colorful, and blemish-free plants as possible. An experiment was conducted using O. regnellii, comparing two irrigation methods, overhead (drip) irrigation versus subirrigation, in addition to varying 20N–2.2P–16.6K fertilizer concentrations, 50, 100, 200, 300, and 500 mg·L−1 nitrogen (N). Overhead irrigation produced larger plants with increased root mass as compared with subirrigation. Low or high fertilizer concentration (50 mg·L−1 N and 500 mg·L−1 N, respectively) led to reductions in the fresh and dry weight of overhead-irrigated plants compared with intermediate fertilizer rates. At the highest fertilizer treatment, plant height was decreased. Chlorophyll index (based on SPAD readings) increased linearly and quadratically for subirrigated and overhead-irrigated plants, respectively. A second study analyzed the effects of seven different fertilizer formulations on growth of O. regnellii and O. triangularis. The fertilizers used in this study were Jack's LX All Purpose (21N–2.2P–16.6K), Peter's Professional (20N–8.8P–16.6K), Jacks Poinsettia FeED Ca-Mg (15N–1.7P–12.5K), Jack's Petunia FeED Mg (20N–1.3P–15.7K), Peter's Professional Peat-Lite Dark Weather Feed (15N–0P–12.5K), Peter's Excel Cal-Mag (15N–2.2P–12.5K), and the slow-release fertilizer Osmocote® (14N–4.2P–11.6K). Growth of both species was significantly reduced by fertilizers that contained little or no phosphorus (P). Current water-soluble fertilizer recommendations of 21N–2.2P–16.6K or slow-release granule fertilizer of 14N–4.2P–11.6K (Osmocote®) produced acceptable, marketable plants, whereas the best O. regnellii and O. triangularis plants were produced using 15N–2.2P–12.5K and 20N–1.3P–15.7K formulations, likely as a result of the additional calcium (Ca), magnesium (Mg), and iron (Fe) in the mixtures.

LOSS OF NUTRIENTS IN A HIGH YIELDING COCONUT PLANTATION THROUGH REMOVAL OF PLANT MATERIALS FROM THE FIELD

High yielding coconut palms absorb large quantities of nutrients from the soil. A high proportion of these nutrients are removed from the field along with the harvest and other plant components. The objective of this study was to determine the rate of macro and micro nutrient removal from the field by Typica x Typica coconut palms, yielding an average of 17,380 nuts per ha. per year, in order to assess the adequacy of the current fertilizer recommendations, to prevent a serious depletion of the nutrient reserves in the soil.Harvested nuts, fallen fronds and inflorescence parts were collected for a two-year period from September 1998 to August 2000 from 10 palms located in a "Madampe series" soil at Bandirippuwa Estate. Their nutrient content was determined by chemical analysis of samples collected from harvested nuts, fallen fronds and fallen inflorescence parts. The reserves of plant nutrients in the soil were determined by chemical analysis of representative soil samples taken from the manure circle and the centre of squares at 0-15 cm and 15-100 cm depths.The amounts of macronutrients lost through the removal of plant components from the site were 116.79 kg N, 14.02 kg P, 245.43 kg K, 40.47 kg Ca, and 33.66 kg Mg per ha. per year. In addition, removal of Na was also observed at the rate of 55.79 kg/ha. Inputs at the recommended rate (4.5 kg of Adult Palm Mixture (APM) and 1.5 kg of dolomite per palm per year) supplied 87.21 kg N, 17.07 kg P, 188.90 kg K, 104.80 kg Ca and 28.59 kg Mg per ha per year (no sodium containing fertilizers were used). The difference between the removal and input should be supplied from reserves of nutrients in the soil. The study showed that except for exchangeable potassium (363 kg/ha), the other macronutrients were present in reasonably high quantities in the experimental site. As the potassium reserves in the soil are low and fertilizer inputs supply only about 77% of the requirement of high yielding coconut (17,380 nuts per ha. per year), soil potassium will deplete rapidly at the current production level. Hence, the depletion should be compensated for either by increasing the 12 quantity of chemical fertilizer or recycling organic products of the palm itself or both. The amounts of micronutrients lost were 1.14 kg Fe, 0.63 kg Mn, 0.13 kg Cu, 0.44 kg Zn and 0.26 kg B per ha. per year. The soil reserve of available iron in the site was so high that a significant depletion of Fe would take more than 300 years. However Mn, Cu and Zn depletion may need attention since reserves in the soil were not very high compared to the rate of removal.

Assessment of nutrient deficiencies in maize in nutrient omission trials and long-term field experiments in the West African Savanna

Low soil fertility is one of the main constraints to crop production in the West African savanna. However, the response of major cereals to fertilizer applications is often far below the potential yields. Low fertilizer efficiency, inadequacy of current fertilizer recommendations, and the ignorance of nutrients other than N, P, and K may limit crop production. Nutrient limitations to maize production were identified in on-farm trials in Togo and in several long-term experiments in Nigeria and Benin. Maize ear leaf samples were analyzed for macro and micro-nutrients, and the Diagnosis and Recommendation Integrated Systems (DRIS) was applied to rank nutrients according to their degree of limitation to maize. In the on-farm trials, both yield and DRIS results indicated that, when N is supplied, P limited maize production in all fields, reducing yields by 31% on average. Sulfur was limiting in 81% of the fields and was responsible for an average yield reduction of 20%. In the long-term experiments where N, P, and K had been annually applied, Ca and Mg indices were strongly negative, indicative of deficiency. Zn indices were negative in all trials. Despite N-fertilizer additions, N indices remained negative in some of the long-term experiments, pointing to low efficiency of applied fertilizers. There was a direct link between DRIS indices and the management imposed in the different experiments, indicating that DRIS is a useful approach to reveal nutrient deficiencies or imbalances in maize in the region.