The influence of micronutrients foliar application on rice(Oryza sativa L.) yield and yield components

Ashkan Daneshtalab Lahijani, Amirabbas Mosavi, Morteza Moballeghi

(Department of Agronomy, Islamic Azad University of Chalous, Chalous, Mazandaran, 46615/397, Iran )

Abstract: 【Objectives】Based on the critical role of micronutrients in rice nutrition and metabolism, the accurate determination of the best period of foliar application as a practical plant nutritional pathway is very important in the novel agricultural production.we assess the influence of micronutrients liquid fertilizer (Fe-EDTA 0.1%, Zn-EDTA 0.05%, B 0.02%, Cu-EDTA 0.05%, and Mn-EDTA 0.05%) on Shiroodi cultivar yield, to understand the optimum times and periods of foliar application of trace elements.【Methods】This investigation was implemented in the Iran Rice Research Institution (Amol, Mazandaran) during two consecutive years(2017−2018).This extensive research was conducted with eight treatments and three replications.The treatments were T0(control), T1 (one foliar application) to T7 (seven foliar applications).The interval of foliar applications was seven days and the first foliar application was finished nine days after transplanting.【Results】The results revealed that the effect of micronutrient application was significant in plant dry weight, grain yield, 1000-grain weight, and harvest index.Also, the interaction of the year and the foliar application was significant in seed Zn content, chlorophyll b, and 1000-grain weight.T4 had a grain yield of 4257 kg/hm2 whereas T0 had a yield of 3499 kg/hm2, indicating approximately 20% of yield enhancement from four times of leaf spraying.The treatment affects grain yield and yield components of rice (Oryza sativa L.cv.Shiroodi) through increasing the number of tillers/plant, improving panicle length, and increasing the number of grains/panicle.【Conclusions】The supply of micronutrients through leaves is an effective procedure in the field of rice due to the higher absorption rate, and spraying 4 times is appropriate.

Key words: rice; foliar application; micronutrients; chlorophyll; grain yield

Rice (OryzasativaL.) is one of the largest cereal crops in the world[1].Because of the definitive role of rice in cuisine and calorie security, it maintains a critical position in the meal supply of Iranian[2].Approximately 50% of the daily calories of the human body is provided by consuming cereals such as rice, wheat and corn.Although rice is in the second place of importance, it is crucial both from a nutritional and economic point of view in Asian countries[3].Since rice provides 21% of the calorie required as well as 15% of human protein needs,both the yield and quality of rice are very important[4].It is clear that the increment of rice yield will be attainable by exerting novel agricultural approaches like advanced nutritional techniques and rice pests and disease management[5].Due to the actuality that the climate of Mazandaran state in the North of Iran is temperate, there is an inestimable territorial potential for increasing rice yield and replacing traditional methods with new agricultural technology.Producing higher quality crops requires the adoption of new plant nutrition methods like foliar spraying[6].Unfortunately, in most instances, lack of proper knowledge in plant nutrient requirements of the selected cultivars of rice during vegetative and reproductive stages has been considered a remarkable impediment for access to intended result.The classifications of micro vs.macronutrients refer to plant requirements rather than plant absorption quantity and they (Zn2+, Fe2+/Fe3+, Mn2+and Cu2+) cannot be taken up by plants in their elemental,or non-charged form, but instead are taken up in an ionic form, with the exclusion of boric acid (H3BO3and H2BO3–)which is uncharged[7].Some biochemical functions of essential micronutrients used in this study are: Manganese (Mn) activates several enzymes in plant cells and is needed for the acting of some dehydrogenases, kinases,oxidases, and peroxidases, and has involved with other cation-activated enzymes and photosynthetic O2evolvement.Actually, the prime specified role of Mn is in the photosynthetic reaction through which oxygen is produced from water[8].Zinc (Zn) is a constituent of alcohol dehydrogenase, glutamic dehydrogenase, and carbonic anhydrase, and it is required for chlorophyll biosynthesis and increases the auxin indoleacetic acid capacity production, and affects the cell division in the apical meristem cells in some species.Iron (Fe) involves with chlorophyll assembly and in enzymes for electron conduction (redox reactions)[7].In this role, it is reversibly oxidized from Fe2+to Fe3+during electron transition.Copper (Cu) acts as a catalyst for respiration, a component of various enzymes involved in redox reaction like iron.An instance of such an enzyme is plastocyanin, which has involved in electron transfer during the light reactions of photosynthesis.Boron (B) complexes with mannitol, mannan, polymannuronic acid, and other constituents of cell walls.Boron has involved in cell elongation and nucleic acid metabolism.The evidence indicates that boron plays role in cell elongation, nucleic acid synthesis, hormone responses, and membrane function.The foliar application is prosperous in tree crops and vines such as kiwi, but it is also used in cereals.The micronutrients applied to leaves could save a farm when basal soil-applied micronutrients are too slow to correct a deficiency[9].The micronutrient absorption by plant leaves is most impressive when the micronutrient solution remains on leaf as a thin film.The successful production of thin-film needs that the nutrient solutions should be supplemented with surfactant chemicals that decrease surface tension.The motion of micronutrient into plant tissue seems to involve dissemination through the cuticle and uptake by leaf cells.In some cases,discrepancies in texture content between macronutrients and micronutrients are not as grand as indicated in the writings.For the remarkable instance, some plant tissues,such as leaf mesophyll, have approximately as much iron or magnesium.Frequently elements are agreeable in concentrations greater than the least demands of plant.The principal sake of most recognized micronutrient shortages has caused by drastic cropping, loss of fertile topsoil apart from, and also detriments of nutrients through leaching[10].Micronutrient deficiency is extending in the agricultural fields.Insufficient amounts of trace elements are popular in the antiquated prospects in the zones with high precipitation and temperature, and where trace element concentrations in parent materials are low[11].The presentment of micronutrient deficiency renders it inconceivable for the plant to gain superlative advantage from primary and secondary macronutrient application.Micronutrients are arranging as effectual elements in the plant metabolism, even if they have been applied in small quantity.The plants cannot complete their life cycle in the inexistence of micronutrients[12].The premier system of fertilizer management is necessary for severe cropping on the same segment of the farm with high yielding varieties and it is known that long-term cropping will change the availability of soil micron utrients[13].Thus, there is an urgent necessity for correcting particular nutrient deficiencies and reducing their further expanse[14].In the rice growing territories, the micronutrient leakage is weighed as one of the basic drawbacks of the diminished efficiency, so the single application of particularly NPK cannot be more practical because of continuous elimination of micronutrients after harvesting as well as losses due to leaching or surface floods[15].The micronutrients deficiency is not only determinative factor of crop productivity reduction, but also deteriorating the products quality.Hosseinzadehetalreported that by evaluating the effect of the concentration and uptake time of micronutrients on yield and yield components of rice ofDeylamaniandShiroodicultivars, grain yield, harvest index, number of tillers and 1000-grain weight had shown significant difference[16].They also reported that the best foliar spraying time was clustering.Furthermore,Liewetalproved that foliar application of copper and boron had a significant effect on reducing contamination of rice plant diseases and so on increasing its yield[15].According to Ziaetalreports, most of the soils were deficient in micronutrient and incapable to aliment crops.The foliar spray has been used in many crops for providing micronutrients, especially iron and manganese[17].For several decades micronutrient spraying has been used for crops to improve yield[18].TheShiroodicultivar was introduced in 2008, which was obtained by intersection ofCaspianandTaromDeylamanicultivars.This cultivar, with high yield and good cooking quality,also has a striking market ability grain shape[19].Based on the results of the other field investigations and perceiving the unfavorable and unexpected yield of rice, especially in the northern provinces of the country, the proper nutrition of rice farms seems to represent a determining factor in improving yield on a large scale.Also, the vital role of micronutrients in plant nutrition, such as increasing the productivity of macronutrients and activating critical enzymes that affect crop performance,the importance of this research and complementary investigations is more significant to designation of the appropriate amount, composition and timing of micronutrients application in relation to the yield and yield components ofShiroodirice.In short, the aim of the research is: would the agronomic characteristics of rice be affected by foliar spraying of micronutrients?And which treatments will be practical and cost-effective for farmers?

1 Materials and methods

1.1 Location and experimental design

The study was conducted at Iran Rice Research Institute farm, Amol, Mazandaran, Iran (52°3′0″ North,26°28′0″ East, 23 m Altitude).This region has moderate summer, cold and dry winter.Furthermore, the research was implemented in two consecutive cultivation seasons.The first year was April–August 2017.The experimental rice variety wasShiroodi, which was supplied by Iran Rice Research Institute.To survey the effect of micronutrients on rice metabolism, traits indicators,yield, and yield components through leaf spraying with the dosage of 2 liters liquid micronutrient fertilizer to 1000 liters of water [the composition of micronutrient liquid fertilizer (w/w, %): Mn 0.05, Cu 0.05, Zn 0.05, B 0.02, Fe 0.1], this investigation was conducted in the form of the randomized complete block design (RCBD).

1.2 Treatments and measurement method

The eight treatments [control (T0), one foliar application (T1) to seven times of foliar application(T7)] were performed with three replications for this trial.Soil samples of 0–30 cm depth were collected from eight various spots in each experimental plot, and after the determination of soil texture, the soil physicochemical properties (Table 1) were determined in laboratory.Thus, fertilizer recommendation was provided based on the soil analysis report.Furthermore,the analysis report indicated that the concentration of soil micronutrients would not cause a significant effect.Each plot had 4 meters length and 3 meters width.The preplanting preparation was finished in early April, 2017.The necessary fertilizers (N, 250 kg/hm2with 40% before transplanting, 30% 21 days after transplanting and 30%35 days after transplanting; P, 150 kg/hm2with 100% before transplanting; K, 200 kg/hm2with 50% before transplanting and 50% 35 days after transplanting) were applied in soil based on the analysis report and rice cultivar recommendation.The first seed cultivation was done in the seedling field in the middle of April.The transplanting was done (traditional method) when the plant height was 20 cm.The same operation was carried out in the second year.The first leaf spraying was conducted 9 days after transplanting and another foliar application was done at 7 days intervals.The field maintenance and use of pesticides were based on standard practices.The data were collected during vegetative (tillering), reproductive (clustering), and harvesting (grain maturation) stages for two consecutive seasons.The sampling operation was done at the middle and end of rice growth stages.Seed Zn content, plant height, leaf color chart (LCC), chlorophyll a, chlorophyll b, carotenoids, plant dry weight, cluster length, grain yield, harvest index, and 1000-grain weight were evaluated in this investigation.The plant samples were collected by quadrate (0.5 m × 0.5 m) and measurements were performed with a caliper.The calculating of plant revenue was done through the elimination of marginal rows and middle plants considered for sampling operation.The total chlorophyll content was measured with a chlorophyll meter (SPAD).To determine the content of chlorophyll a, b and carotenoids, the pigments were extracted using methanol, and the amount of light absorbed was measured using a spectrophotometer[20].Using a puncture part in the middle part of leaf selected for the extraction.The selected parts were placed in 20% methanol solution and kept in the fridge for 24 hours.After that, the pigments were separated by an extraction pump and placed inside a spectrophotometer for the determination of the percentages of chlorophyll a, chlorophyll b, and carotenoids based on their wavelength.The zinc content in rice grain was measured by atomic absorption spectrometry and dry ash method[21].The grain sample was placed in an oven at 550℃ for 8 hours.The resulting ash was then removed, and a few drops of distilled water were added followed by 3 mL of hydrochloric acid(2 mol/L) before placing the sample at 70℃ for 60 minutes.Finally, the sample was diluted to a volume of 50 mL in a balloon with distilled water and measured at a wavelength of 9.213 with an atomic absorption apparatus for the zinc content.The leaf color chart (LCC) was used to determine the leaf greenness.Based on the instructions of the leaf color chart, leaf color was measured 13 days after transplanting using LCC during two separate steps.The leaf color chart was measured from 2 to 4 pm.To measure the leaf color chart, at least 10 disease-free leaves were selected from the central part of each plot.The longest leaf of each tiller was selected, and the middle part of the leaf was placed on the LCC.During the collecting period, plant height, cluster length, 1000-seed weight, economic yield, biological yield, and harvest index were evaluated.For evaluation of the economic yield, 80 plants were harvested from the middle part of the plots, and after threshing, the moisture content of seeds was measured using a hygrometer.The weight of 1000 seeds was assessed by counting ten hundred samples and their weight was obtained based on a moisture content of 12%.For calculating the harvest index, five plants were harvested from each plot, and the plants were kept in the field for 24 hours until the moisture content reached about 13%.After threshing, grain and straw weights were measured and the harvest index wascalculated as a percentage of economic yields in the biological yield.

表 1 供试土壤理化性状Table 1 Soil properties of the experimental field (Soil depth 0−30 cm)

1.3 Data analysis

The variation analysis was done at the end of each year, in compliance to experimental design.The diagrams were drawn by Microsoft office word and Excel software.The collected data were subjected to analysis the variations performed utilizing the SAS program to discover the statistical significance of the foliar application effect.When theF-values were significant, LSD test was performed for means comparison.

2 Results and discussion

2.1 Seed Zn content

The results of combined analysis of variance showed that the effect of foliar application of micronutrient fertilizer on the content of zinc in rice grain was significant at 1% level of probability.Also, the interaction of year and foliar application was significant in this regard (Fig.1).The comparison of the biennial means of seed Zn content indicated that the highest content (about three times more than the average value) was in T6 (67.02 mg/kg), while the control had the lowest one.Foliar application of zinccontaining micronutrient fertilizer at various vegetative and reproductive stages of rice increased the content of zinc in grain.Jiangetal[22]reported this could be related to the connections among the xylem and phloem vessels in the wheat panicle and the interchange of elements between them.Also, Ishimaruetal[23]noted that zinc was stored in the plant after being absorbed through the stomata and transferred to the leaves.This causes the transfer of zinc from senescing leaves at the end of the growth period through the phloem to the seed.

图 1 微量元素叶面喷施对籽粒锌含量的影响Fig.1 Effects of micronutrients foliar application on the Zn content in rice seed

2.2 Leaf greenness

The difference in leaf color chart number was significant at the 1% level of probability (Fig.2).But the interaction of foliar application and year was not significant.T4 retained the highest number of leaf color chart (3.83)forShiroodicultivar while the control had the lowest value (2.54).The facilitating processes related to N metabolism, improving the rate of decomposition and synthesis, as well as accelerating nitrogen reduction reactions are some of the factors that may have contributed to the significance in leaf color chart in foliar spraying treatments compared to the control.It suggests a significant increment in the productivity of basal nitrogen fertilizers used in the experiment.In this regard, Maralianetal[27]also reported that micronutrient foliar application caused a significant effect on traits like LCC, number of tillers,and some fertile tillers at a probability level of 1 percent.

图 2 微量元素叶面喷施对水稻叶绿度的影响Fig.2 Effects of micronutrients foliar application on the leaf greenness of rice

2.3 Leaf chlorophyll content

The content of chlorophyll a was affected by the integrated foliar application of essential micronutrients at 1% level of probability (Fig.3A).The highest content of chlorophyll a was in T4 treatment (0.56 mg/g, FW).The lowest content was in T2 treatment (0.29 mg/g, FW).It is possible that the foliar spray of micronutrients that plays a crucial role in the synthesis of chlorophyll like zinc,iron, and copper could prove a significant efficacy on augment the pigment content of leaf cells.In a similar study by Singhetal[24], they reported that the phenological response of rice to various levels of micronutrients was significant under calcareous soil conditions in all treatments, especially in the tillering stage except for full flooding treatment.The application of zinc alone or in combination with boron increased the chlorophyll content of rice.

The content of chlorophyll b was affected by the foliar application of micronutrients as could be seen(Fig.3B).The interaction between year and micronutrients foliar application was significant.The comparison of the means of two years indicated that the highest chlorophyll b content was in T4 treatment (1.42 mg/g, FW) and the lowest content was in T6 treatment(0.88 mg/g, FW).The concurrent supply of indispensable micronutrients seems to affect the percentage formation of chlorophyll pigments.This event provided a remarkable influence on photosynthesis rate through the increment of light absorption and accelerates of the relevant processes.Although some of micron utrients applied prove the direct role in the enhancement of nitrogen fixation.A similar study by Zayedetal[11]reported that chlorophyll content (SPAD index) was improved as a result of gaining micronutrients.Further, the treatment of iron,zinc and manganese was found to have the highest effects on the traits.

图 3 微量元素叶面喷施对水稻叶片叶绿素含量的影响Fig.3 Effects of micronutrients foliar application on chlorophyll content of rice

2.4 Carotenoids content in leaf

The content of carotenoids was significantly increased in treatments T1 to T7 compared to the control (Fig.4).The interaction of foliar application and year was significant.The highest carotenoids content was in T4 treatment (0.429 mg/g, FW) and the lowest carotenoids content was in T2 treatment (0.258 mg/g, FW) Because of the determinant function of micronutrients used like zinc and copper, they may have played an important role in the structure of vital enzymes and facilitating the intracellular reactions related to the production procedure of carotenoid.Conferring on to the Gómez-Garcíaet al[25]the increase in the content of carotenoids in the foliar spraying treatments compared to the control is due to the determinate role of applied elements, which is the theories proposed in this field.Pursuant to most accepted theories, carotenoids have synthesized by the three genes as well as several enzymes involved in the synthesis of pigments in chili peppers, although few concepts have known about the molecular mechanism of this process.

图 4 微量元素叶面喷施对水稻叶片类胡萝卜素含量的影响Fig.4 Effects of micronutrients foliar application on the carotenoids content of rice leaf

2.5 Plant height, panicle length and plant dry weight

The effects of foliar application of micronutrient fertilizer on plant height was significant (Table 2), and the interaction between foliar application and year was not significant.On average of the two years, the highest plant height was found in T4 treatment (156.8 cm), and the lowest was in the control (142.7 cm).The increase of plant height in the foliar application treatments has expected to a significant increase in stem length due to an increment in the internode length as a result of enhanced production of plant growth regulators like IAA,which plays a critical role in developing the cell division and photosynthesis rate.Arifetal[26]reported that combined foliar application of zinc and boron was the best fertilizer balance for further growth and yield response of rice.As well as for increases in some traits like plant height, number of tillers, panicle length,number of filled seeds per plant, number of fertile panicles, and dry weight was affected by mentioned nutrients.

Panicle length is related to the number of grains.The results showed that the effect of micronutrients fertilizer foliar application on length of panicle, as well as its interaction with year, was not significant (Table 2).The highest panicle length was in T3 (30.8 cm) while the lowest was in the control (28.1 cm).Micronutrient foliar application led to an increase in the transfer of nutrients and productivity of these elements along with regulating plant hormone levels, and enhancement of cell division has many effects on panicle length and fertility.A similar study by Zayedetal[11]reported that plant dry weight,leaf area index, chlorophyll content along with plant height and panicle length were significantly increased compared to the control after receiving micronutrients.

表 2 微量元素叶面喷施对水稻株高、穗长及植株干重的影响Table 2 Effects of micronutrients foliar application on plant height, panicle length and plant dry weight of rice

2.6 Grain yield and yield components

Grain yield of T1 to T7 treatments was higher than that of the control (Table 3), which was the same as the results of the traits such as the number of tillers per area and number of panicles per plant.Based on the average of two years, the highest grain yield was in T4 treatment(4257 kg/hm2) while the lowest was in the control (3499 kg/hm2).Foliar application of micronutrients may have played a direct role, the inoculation by manganese, grain formation and maturation by boron, and activation of enzymes responsible for protein synthesis by zinc.Furthermore, iron facilitates the reduction of nitrate and sulfate processes, and copper accelerates the metabolism of carbohydrates.And Mahendraetalstated that the application of zinc sulfate affected the number of tillers per area, plant height, number of seeds per panicle, 1000-seed weight, harvest index, and biological yield[28].

There was also a significant increase in the availability of macronutrients.The 1000-grain weight was affected by zinc, iron, manganese, boron and copper compared to the control treatment (Table 3).Additionally, the interaction effect of foliar application and the year displayed a significant difference.On average, over two years the highest 1000-grain weight was in T4 treatment(29.8 g) while the lowest was in the control (25 g).It is likely that enhancing the productivity of macronutrients,and increasing the fertility of clusters, have interpreted the most influential role in enhancement the 1000-grain weight.Hosseinzadehetal[16]also reported that foliar application time caused a tangible and significant effect on the number of filled seeds per panicle, 1000-grain weight, and greatest grain yield.The foliar application at 40 days after transplanting achieved the most enormous effect.In a study on the zinc foliar application on maize,Ghazvinzadehetal[29]reported that with increasing of the quantity of element application, several traits increased,including 1000-grain weight, the number of grains per panicle, the content of available Zn in corn seed, grain protein content.

In this experiment, the effect of the number of micronutrient foliar applications on the rice harvest index was significant (Table 3).The highest harvest index was in T4 (42%), while the lowest harvest index was in the control (34%).By influencing the yield-related indices and crop components, it was clear that the harvest index was affected by micronutrient spraying.So, it was possible that increasing grain yield had a direct influence on the harvest index.In a similar study, Ghasemietal[30]reported that the highest harvest index and greatest 1000-grain weight were gained under the interaction of zinc,iron, and manganese sulfate fertilizers.

表 3 微量元素叶面喷施对水稻产量、千粒重和收获指数的影响Table 3 Effects of micronutrients foliar application on the grain yield, 1000-grains weight, and harvest index of rice

3 Conclusion

The statistical results revealed that the effect of micronutrient foliar application was significant on plant dry weight, seed yield, 1000 grains weight, and harvest index.Also, the interaction of year and foliar application was significant on seed Zn content, chlorophyll b, and 1000-grain weight.Among the treatments, T4 treatment with 4257 kg/hm2grain yield, compared to the control yield of 3499 kg/hm2, showed approximately 20% of yield increase by four foliar applications.The yield enhancement was through an increase in the number of tillers/plant, improvement of panicle length, and increase in the number of grains/panicle.The micronutrients supply through leaves is an effective method due to the high absorption velocity.Due to the low mobility of micronutrients in soil, foliar spraying of essential nutrients is a determinative factor in plant nutrition and the improvement of rice production.