Cropping pattern based micronutrient application for wheat-mungbean-T . aman crop sequence under Tista Meander Floodplain soil at Rangpur

Intensification of agricultural land use coupled with cultivation of modern varieties has remarkably increased in Bangladesh. This in turn has resulted in deterioration of soil fertility, with emergence of macroand micro-nutrient deficiency of crops. With this point in view, a study was undertaken to evaluate the effect of different micronutrients on crop yield, and to determine the requirement of selected micronutrients for crops and cropping patterns in the Tista Meander Floodplain (AEZ 3). Experiments were conducted at BINA substation and farmers’ fields of Rangpur district within AEZ 3. In experiment 1, the field trials were done with six micronutrients (B, Zn, Cu, Mn, Fe & Mo) designed in an additive manner. These elements were imposed to the first crop and their residual effects were monitored on the next two crops over the patterns: wheat-mungbean-T. aman. The rates of micronutrient application were 3 kg Zn, 2 kg B, 2 kg Cu, 3 kg Mn, 5 kg Fe and 1 kg Mo per hectare, added as fertilizers such as ZnSO4.7H2O, H3BO3, CuSO4.5H2O, MnCl2, FeSO4.7H2O and Na2MoO4, respectively. Other nutrients viz. N, P, K & S were applied at recommended rates to all plots; rationale was followed for the second and third crops. Intercultural operations were done whenever required. The results revealed that across the experimental sites, the crops were quite responsive to the added Zn and B. Positive effect of Cu was also noted in some cases. In the following year (expt. 2), two micronutrients, Zn and B were taken into the same cropping pattern and designed in a way to determine whether 1crop, 2crop or 3crop application is necessary to achieve satisfactory crop yield. The rates of Zn application were 0, 2, 4 & 6 kg ha, and the rates for B were 0, 1.5 and 3 kg ha. The results show that Zn application at 4 kg ha coupled with B application at 1.5 kg ha to the first crop can meet their requirement for the subsequent two crops in a pattern. The present study suggests that cropping pattern based field trials with Zn, B and Cu need to be done at farm level in the high cropping intensity areas of this country in order to determine micronutrient requirement of crops.


Introduction
The fertility status of soils is variable and in most of the areas in Bangladesh it has declined.The soil in Tista Meander Floodplain (AEZ 3) is moderately acidic throughout, low in organic matter content on the high land, but moderate in the low lands.Fertility level, in general, is low to medium (Banglapedia, 2015).Texturally the soils are loam and sandy loam.Intensification of agricultural land use has increased remarkably and the cropping intensity has increased from 143% in 1971-72 to about 191% in 2014-2015(Krishi Diary, 2016).Cultivation of high yielding varieties for all crops has increased remarkably.Consequently, this has resulted in deterioration of soil fertility with emergence of micronutrient deficiency.In this country, chronologically N, P, K, S, Zn and B deficiencies have appeared in soils and crops of Bangladesh.Among the micronutrients, next to zinc, boron deficiency is prominent in soils of Dinajpur, Rangpur, Bogra, Sirajganj, Mymensingh, Comilla and Sylhet district (SRDI, 2010).In early 1980s, S and Zn deficiency in rice was observed in Bangladesh (Jahiruddin et al., 1981).Boron deficiency of some crops was reported (Jahiruddin et al., 1995) in early 1990's.There is sporadic information of Cu, Mo and Mn deficiencies in crops (Bhuiyan et al., 1998).Micronutrients are required for supporting normal growth and development of plants.Micronutrients that are essential for crops include Fe, Mn, Zn, Cu, Mo, Cl and B. Micronutrient trials have been made principally on rice (Jahiruddin et al., 1994), wheat (Hossain, 2005) and maize (Hossain et al., 2008).However, cropping pattern based micronutrient research is limited.The importance of Zn in crop nutrition has received considerable attention during eighties in Bangladesh.Zinc deficiency is particularly evident in calcareous and wetland rice soils (SRDI, 2008).Zinc deficiency in crops reduces not only the crop yield, but also hampers nutritional quality (Cakmak, 2008).Although taken up in small quantities, boron deficiency may lead to serious consequences regarding economic yield of various crops like wheat, mustard (Islam, 2008).Light textured soils of the country are deficient in plant available boron where significant leaching loss of borate ions occurs.Gupta (1979) states that because of non-ionic nature, boron is once released from soils it can be leached out from soils fairly rapidly.In Bangladesh, boron deficiency is more common in rabi crops (dry season), as observed in wheat (Jahiruddin, 2011), mustard (Hossain, 2007), chickpea (Johnson et al., 2005) and lentil (Srivastava et al., 2000).Cooke (1982) suggested that when the hot water soluble B in soil is less than 0.5 μg g -1 , deficiency is likely to occur and all crops are to be treated with B. Rashid et al. (2009) have shown 15-25% increase in grain yield of rice over N, P and Zn coupled with appreciable improvement in grain and cooking quality with application of B. Research is needed to determine all the deficient elements, whether macronutrients or micronutrients.Fertilizer management is needed on sustainable basis.Fertility management system that is profitable in short-term and sustainable in long-term should be formulated and it needs to be confirmed by on-farm research trials.Keeping the above points in view, the present study was carried out to evaluate the effect of micronutrients application on the yield of wheat, mungbean and T. aman rice crops and to find out the optimum rate of micronutrients for the wheatmungbean-T.aman cropping pattern in AEZ 3.

Materials and Methods
Experiments on a dominant cropping pattern of wheatmungbean-T.aman were set up at BINA substation and farmers' fields at Rangpur Sadar in 2011-2012 (experiment 1 in two locations) and in 2012-13 (experiment 2) at Kaunia upazila under Rangpur district.The objectives were to evaluate the effects of different micronutrients on the crop yield and to see the direct and residual effects of Zn and B as to determine the requirement of Zn and B for the wheat-mungbean-T.aman cropping sequence.Experiment 1 with seven treatments was set up in November 2011 in two locations with wheat the first crop of the cropping pattern followed by mungbean as a legume (2 nd crop) and T. aman rice (3 rd crop).Control (No use of micronutrients) T 2 : Zn T 3 : Zn + B T 4 : Zn + B + Cu T 5 : Zn + B + Cu + Mn T 6 : Zn + B + Cu + Mn + Fe T 7 : Zn + B + Cu + Mn + Fe + Mo These micronutrient treatments were imposed on the first crop only (Expt.1).Their residual effects were observed on the next two crops over the year.The rates of micronutrients were 3 kg Zn, 2 kg B, 2 kg Cu, 3 kg Mn, 5 kg Fe and 1 kg Mo per hectare.The elements were added as ZnSO 4 .7H 2 O (23% Zn), H 3 BO 3 (17% B), CuSO 4 .5H 2 O (25% Cu), MnCl 2 (17% Mn), FeSO 4 .7H 2 O (19% Fe) and Na 2 MoO 4 (39% Mo), respectively.Other nutrients viz.N, P, K & S were used at recommended rates for all plots (for wheat 100-20-60-10, mungbean 20-15-25-8 and T. aman 90-15-40-10 kg ha -1 N-P-K-S, respectively from Urea, TSP, MoP and Gypsum); rationale was followed for the second and third crop within a year.For the wheat, one-third urea was applied at final land preparation and the rest was applied at an equal rate during tillering and booting stages.For the rice, the one-third urea was applied after seven days of transplanting and the rest at an equal rate during the maximum tillering and panicle initiation stages.For mungbean, the one-third urea was added before sowing, another one-third after 25 days of sowing and the rest urea after 50 days of sowing.The experiment 1 was conducted at BINA substation farm and in a farmers' field both at Rangpur.The experiment 2 was conducted at Kaunia, Rangpur in a farmers' plot.Before conducting field experiments soil samples were collected and analyzed.The soil properties are presented in Table 1.Data on grain and straw/stover yield of crops were recorded and analyzed statistically following Duncan's New Multiple Range Test (DMRT).
Results from expt. 1 (Table 2) revealed that the effect of Zn addition was distinct in wheat.Next to Zn, the B effect was positive.With this end in view, Zn and B treatments were designed for next year experiment (expt.2) to ascertain whether 1st-crop, 2nd-crop and 3rd-crop application is required in 1 year-crop cycle as follows: Economic analysis was done following the principle of partial budget analysis (Kay, 1981).Marginal benefitcost ratio (MBCR), the ratio of marginal or added benefits and costs, is the indicative of the superior treatments.Only variable costs i.e. chemical fertilizer was taken into account as added cost for each cropping system.The benefit was calculated based on yield (main product and by-product).

Wheat
To compare different treatments with control treatment the following equation was used.

Results and Discussion
Regarding effects of different micronutrients on crops (expt.I), it appeared that there was a significant positive effect of micronutrient application on the grain yield of wheat (Table 2).At both locations, the effects of Zn were pronounced and next to Zn, the effect of B was remarkable.Residual effect of Zn and B was also noticed in following mungbean (Binamung-8) and T. aman rice (Binadhan-7) crops.In farmers' field, though soil available status of Cu and Mn were high (3.04 µg g -1 and 57 µg g -1 , respectively), positive effect of Cu and Mn was found in wheat (grain yield enhancement in farmers' field was mainly due to increase in effective tiller m -2 for Cu and Mn application even the soil was not deficient) and their residual effect on the following mungbean crop.
From expt.I, it is apparent that across the locations and crops, the effect of Zn is quite clear.Next to Zn, the B effect was quite positively responsive.Thus, further field trials were designed to determine an optimum rate of Zn and B application and to ascertain whether 1st-crop, 2ndcrop and 3rd-crop application is required in 1 year-crop cycle towards that end.

Effects of Zn and B on the yield of crops in wheatmungbean-T. aman cropping sequence Grain yield of wheat:
There was a significant positive effect of Zn and B application on grain yield of wheat (BRRI gom25) (Table 3).The grain yield ranged from 3.65-4.86t ha -1 over the treatments.The Zn-B fertilization resulted in 8-18% increase in grain yield over control treatment.Treatment T 3 (Zn at 4 kg ha -1 and B at 1.5 kg ha -1 ) recorded the highest yield (4.86 t ha -1 ) and was identical to T 4 (Zn at 6 kg ha -1 and B at 3 kg ha -1 , 4.42 t ha -1 ).In terms of grain yield, the treatments can be ranked in the order: T 3 > T 4 > T 2 > T 1 .The result clearly indicated yield advantage for Zn & B application along with the recommended rates of NPKS application in wheat.Application of N, P, K and S at a recommended rate with no micronutrients (i.e.control) had the minimum grain yield (3.65 t ha -1 ).Chaudhary et al. (2010) recorded the highest and 11.8% increased grain yield of wheat by application of 5 kg Zn ha -1 and over control in rice-wheat cropping pattern.Keram et. al. (2014) observed the application of 20 kg Zn ha -1 along with recommended basal dose of NPK on wheat crop enhanced both grain and straw yields.Boron deficiency is now a world-wide problem for field crop since it affects the flowering and plant reproductive process and therefore directly affects harvested yield (Bolanos et al., 2004).Ahmad et al. (2012) in an extensive review observed an increase in yield of 14% in wheat with B fertilization by using appropriate rates, methods and sources on B-deficient soils.Nadim et al. (2011) found that use of B at 2 kg ha -1 produced higher leaf area index, enhanced crop growth rate, number of grains plant -1 and grain yield of wheat (cv.Gomal-8).Khanom (2013) observed B application at 1.5 kg ha -1 to the 1st crop can meet up their requirement for the subsequent crops in a pattern.Straw yield of wheat: Like grain yield, the straw yield of wheat was also significantly influenced by Zn-B treatments and the yield ranged from 4.77-6.29 t ha -1 (Table 3).Treatment T 3 (Zn at 4 kg ha -1 and B at 1.5 kg ha -1 ) with NPKS gave the maximum straw yield (6.29 t ha -1 ) which corresponded to the maximum grain yield over the control yield (4.77 t ha -1 ).The treatment T 3 was found identical to the treatment T 2 (Zn at 2 kg ha -1 and B at 1.5 kg ha -1 , 5.62 t ha -1 ) and T 4 (Zn at 6 kg ha -1 and B at 1.5 kg ha -1 , 6.13 t ha -1 ) treatments.Application of recommended rate of macronutrients without any micronutrient (control treatment) showed the minimum straw yield.Treatments based grain yields followed the order as T 3 > T 4 > T 2 > T 1 .

Seed yield of mungbean:
There was a significant residual effect of the Zn-B treatments on the second crop, mungbean (Binamung-8) in the wheat-mungbean-T.aman sequence of 1-year crop cycle.The seed yield ranged from 1.63-2.14t ha -1 over the treatments (Table 3).Treatment T 2.1 (Zn 2 kg ha -1 and B 1.5 kg ha -1 applied to wheat) produced the maximum seed yield (2.14 t ha -1 ) which was statistically identical with T 2.2 (Zn 2 kg ha -1 and B 1.5 kg ha -1 addition to the first crop and Zn 2 kg ha -1 at the second crop, mungbean, 1.98 t ha -1 ), T 2.3 (Zn 2 kg ha -1 and B 1.5 kg ha -1 addition to wheat and again to mungbean-2nd crop, 2.05 t ha -1 ), T 3.1 (Zn 4 kg ha -1 and B 1.5 kg ha -1 addition to the wheat, 2.02 t ha -1 ) and T 4.1 ( Zn 6 kg ha -1 and B 3 kg ha -1 addition to wheat, 1.94 t ha -1 ) treatments.Seed yield of mungbean responded significantly to the application of Zn-B showing that the treatment T 2 (Zn at 2 kg ha -1 and B at 1.5 kg ha -1 to wheat), T 3 (Zn at 4 kg ha -1 and B at 1.5 kg ha -1 to wheat) and T 4 (Zn at 6 kg ha -1 and B at 3 kg ha -1 to wheat) added to the wheat was enough to support the mungbean yield which was identical to the yield obtained with renewed application of only Zn (Zn 2 B o ) or Zn-B (Zn 2 B 1.5 ).These results showed that the seed yield did not respond to further only Zn or Zn-B combined application.It appeared that application of 2, 4 or 6 kg Zn ha -1 and 1.5 kg B ha -1 to the 1st crop (wheat) was optimum to obtain satisfactory yield of both the 1st and 2nd crops.The lowest seed yield (1.63 t ha -1 ) was recorded in Zn-B control treatment.The Zn-B supply resulted in 16-23% seed yield increase of mungbean over control.Application of 2 kg Zn and 1.5 kg B ha -1 in the previous wheat crop resulted in 23% seed yield increase of mungbean over Zn-B control.The present study clearly indicated that residual effect of Zn-B was enough to get satisfactory yield of mungbean seed yield without further application of Zn or Zn-B to the 2nd crop (mungbean) (Table 2).Gentry (2011) stated that mungbean was very responsive to Zn where soil test level was below 0.4 μg g -1 on acid soils.Hossain et al. (2008) found optimum rate of Zn for

Treatments
BINA substation Farmers' field the maize-mungbean-rice cropping system to be 4-0-2 kg ha −1 for the 1st year and 2-0-2 kg ha −1 for subsequent years particularly when mungbean residue was removed, and such rates for mungbean residue incorporation being 4-0-1 and 2-0-1 kg ha −1 , respectively.Rahman et al. (2015) stated that seed and stover yields of mungbean increased with increasing levels of P and Zn up to certain level.Shekhaw et al. (2012) in a sunflowermungbean cropping system, 1.5 kg boron ha -1 applied to the sunflower crop and found optimum in the succeeding mungbean crop in terms of yield, yield attributing characters, B concentrations and uptake, productivity and residual nutrient status for the system.Hossain et al. (2013) recorded the highest mungbean yield from recommended fertilizer dose (N-P-K-S-Zn @ 20-20-30-10-4 kg ha -1 plus B (@1 kg ha -1 ) treated plot of wheat crop in the research field of Wheat Research Centre, Dinajpur, Bangladesh.
Stover yield of mungbean: Significant residual effect of Zn-B application on the stover yield of mungbean was also observed (Table 3).The stover yield ranged from 2.33-3.16t ha -1 over the treatments.The stover yield obtained with treatment T 2.2 (Zn 2 kg ha -1 and B 1.5 kg ha -1 to the first wheat crop and only Zn 2 kg ha -1 to the second mungbean crop) showed the maximum stover yield (3.16 t ha -1 ) which was statistically identical with treatments T 2.1 , T 2.3 , T 3.1 and T 4.1 .The addition of Zn and B or residual effect yielded always higher stover yield over control (without Zn-B).The Zn-B addition increased 16-26% stover yield over Zn-B control.
Grain yield of T. aman rice: There was a significant and positive effect of Zn-B application on the grain yield of T. aman rice (3rd crop in the pattern).All the Zn-B treatments (T 2.1.1-T4.1.1 ) gave significantly higher (7-28%) grain yield over the control treatment (T 1.1.1 , only NPKS).The rice grain yield varied from 3.41 t ha -1 as recorded minimum with the absolute Zn-B control to 4.79 t ha -1 obtained with T 2.2.2 (Zn addition at 2 kg ha -1 and B at 1.5 kg ha -1 to first crop, wheat and only Zn at 2 kg ha -1 to the second and third crops, T. aman rice).
Statistically identical grain yield was found between T 2.3.1 (Zn at 2 kg ha -1 and B at 1.5 kg ha -1 to first cropwheat and second crop-mungbean, 4.47 t ha -1 ) and T 2.3.2 (Zn at 2 kg ha -1 and B at 1.5 kg ha -1 to the first crop and the second crop, again only Zn at 2 kg ha -1 to the third crop, T. aman rice, 4.40 t ha -1 ) treatment (Table 3).Maharana et al. (1993) observed a significant response of rice yield to ZnSO 4 application in both kharif and rabi seasons.Rashid et al. (2009) quantified rice yield increase by 15%-25% over control with the application of 1 kg B ha -1 , coupled with appreciable improvement in grain/cooking quality with application of B in Pakistan.
Straw yield of T. aman rice: As in grain yield, the straw yield of T. aman rice was markedly influenced due to Zn-B treatments (Table 3).The straw yield ranged from 3.81-5.33t ha -1 noted in the different treatments.
The lowest straw yield was recorded with absolute Zn-B control and the highest yield with treatment T 2.3.2 (Zn at 2 kg ha -1 and B at 1.5 kg ha -1 to 1st crop-wheat and 2nd crop-mungbean, again Zn 2 kg ha -1 to the third crop, T. aman rice).

Fig. 1 .
Fig. 1.Percent grain yield increase of wheat due to micronutrients application over control

Table 2 . Effects of micronutrients on the grain and straw yields of wheat, mungbean and T. aman in the wheat-mungbean-T. aman crop sequence
Means followed by same letter in a column are not significantly different at 5 % level by DMRT, SE (±) = Standard error of means, CV= Coefficient of variation, *= Significant at 5 % level, **= Significant at 1% level

Table 3 . Effects of micronutrients on the grain and straw yields of wheat, mungbean and T. aman in the wheat-mungbean-T. aman crop sequence and partial economic analysis for different treatments
Means followed by same letter in a column are not significantly different at 5 % level by DMRT, SE (±) = Standard error of means, CV= Coefficient of variation, **= Significant at 1% level, *= Significant at 5% level