Response of Greengram (Vigna radiata L.) as Succeeding Crop to Residual Effect of Micronutrients Mixture Administered in Preceding Sweet corn [Zea mays (L.) Saccharata]

In many parts of India, the emerging cropping system (cereal based legume cropping system) is maize followed by pulses (Rani et al., 2022). Most farmers do not plant anything on their land after harvesting sweet corn, even though there is a lot of potential for growing another crop during the rabi season. In India, pulses, also referred to as food legumes, are produced and consumed second only to cereals. The word "pulse" is derived from the Latin word "puls", which means "pottage" i.e., seed boiled to make porridge or thick soup (Kavya et al., 2021). For vegetarians, pulse is an excellent source of energy, minerals, vitamins and dietary protein (25%). It is not only a vital source of food for humans and animals, but it is also essential for maintaining soil fertility. In addition to enhancing the physical characteristics of the soil, these pulses fix atmospheric nitrogen and are primarily grown as a sequence crop or intercrop alongside other cereal crops. Greengram is one of the most important choice available to farmers as it boost their income, while utilizing the nutrients and remaining moisture in the soil.

One of the most significant pulse crops in India is the greengram (Vigna radiata L.), a short-duration crop that fits into a variety of cropping systems (Thesiya et al., 2019). It is a staple food high in protein, with about 25% of its protein coming from the leguminaceae family, which means it has the ability to fix nitrogen from the atmosphere. Its origins are in Central Asia and India.

Greengram (Vigna radiata L.), a short duration crop that fits into a variety of cropping systems, is one of the most important pulse crops in India. It is a staple food high in protein, with about 25% and belongs to leguminaceae family, which has the ability to fix atmospheric nitrogen. It is originated from India and Central Asia (Kavya et al., 2021). In India, greengram is produced on an average of 1.51 mt across an area of about 3.27 mha. Karnataka has 2.05 lakh hectares of total mungbean cropland, producing 0.67 lakh tonnes and yielding 324 kg ha^-1 (Anonymous, 2023).

Hedge (1998) asserts that providing nutrient sources to the previous crop has a significant positive impact on the subsequent crop. A study was conducted to ascertain whether the foliar application of a micronutrients mixture (MM) in the previous kharif sweet corn crop had any lasting effects on the productivity and profitability of the subsequent greengram crop, taking into account the previously mentioned factors.
 

Experimental site

The field experiment was carried out in the rabi seasons of 2022 and 2023 at the College of Agriculture, V.C. Farm, Mandya, University of Agricultural Sciences, Bangalore, Karnataka, India at 695 meters above mean sea level. The location of the experiment is 12°57'N latitude and 76°83'E longitude. The sandy loam type of soil used in the experiment has the following properties: At the initiation of the experiment, the following values were recorded: pH- 7.5, EC- 0.17 dS m^-1, soil organic carbon- 0.48%, available nitrogen- 263.78 kg ha^-1, available phosphorous- 48.45 kg ha^-1 and available potassium- 251.84 kg ha^-1.

Treatment and experimental design

The experiment was set up in randomized complete block design with ten treatments replicated thrice viz., T₁: Absolute control, T₂: Recommended package of practices, T₃: Foliar spray of MM₁ (0.1%), T₄: Foliar spray of MM₂ (0.2%), T₅: Humic acid spray @ 0.5%, T₆: Biostimulant spray @ 625 ml ha^-1, T₇: Foliar spray of MM₁ + Humic acid spray @ 0.5%, T₈: Foliar spray of MM₂ + Humic acid spray @ 0.5%, T₉: Foliar spray of MM₁ + Biostimulant spray @ 625 ml ha^-1 and T₁₀: Foliar spray of MM₂ + Biostimulant spray @ 625 ml ha^-1. The study was carried out at the same location the following year to evaluate any lingering effects in greengram, with the treatment's randomization remaining unchanged. The composition of micronutrients mixture is Zn, Mn, Fe, Cu and B. MM₂ is double the concentration of MM₁. The biostimulant used in the present study is macarena (seaweed extract).

The greengram variety KKM-3, released from ARS, Kathalagere, Karnataka was sown on September 30^th, 2022 and September 29^th, 2023, respectively, without any treatment imposition after the previous crop’s stubbles (sweet corn) were incorporated into the soil in 4.8 m × 4.2 m plots, maintaining a spacing of 30 cm × 10 cm between rows and plants in a randomized block design with three replications. For all treatments other than absolute control, the recommended dose of fertilizer for greengram (25:50:50 kg N, P₂O₅ and K₂O ha^-1) was administered. Irrigations were applied based on need.

Data collection

Each net plot's growth and yield parameters were noted after five representative plants at random and tagged. During the crop growth period, all subsequent observations were made on the chosen plants. Matured pods from the net plot area were picked manually and dried in the sun. Following threshing, the weight of the cleaned seeds obtained from each plot was noted. Five plants that were designated to record post-harvest observations had their net plot seed yield added and it was expressed in kg ha^-1.

Net return and benefit-cost ratio

To determine which treatment is the most profitable, all costs related to cultural operations from pre-harvest tillage to harvesting, including additional treatment costs were calculated and deducted from each treatment’s gross income in order to determine net monetary returns per hectare. Gross income was calculated using the current market prices. For every treatment, the B: C ratio was computed by dividing the net return by the cost of cultivation.

Fisher's method of analysis of variance as out lined by Gomez and Gomez (1984) was employed for statistical analysis of the obtained experimental data. The F test was conducted with a 5% level of significance. When the F test was significant, critical difference (CD) values are provided for the data at the 5% level of significance.
 

Growth parameters
 
The pooled data in Table 1 and 2 indicated that the growth characteristics of the greengram were significantly impacted by the various foliar applications of the micronutrients mixture used in the previous kharif sweet corn crop. Significantly higher number of branches plant^-1 at 30 DAS (2.73), 45 DAS (4.18) and at harvest (8.67) was observed under the treatment receiving foliar application of MM₂ (0.2%) along with humic acid @ 0.5% sprayed at 30 DAS. However, lower values were recorded in absolute control (1.16, 2.11 and 5.18, respectively) at 30, 45 DAS and at harvest. Similar trend was obtained with respect to dry matter accumulation at 30, 45 DAS and at harvest. The foliar application of MM₂ (0.2%) along with spraying of humic acid @ 0.5% at 30 DAS registered significantly higher dry matter accumulation (1.29, 5.64 and 14.19 g plant^-1, respectively). Absolute control recorded significantly lower dry matter accumulation (0.66, 3.30 and 8.30 g plant^-1, respectively).




The treatment which received foliar spray of MM₂ (0.2%) + Humic acid @ 0.5% in previous sweet corn crop was found superior over other treatments in obtaining significantly higher growth parameters in succeeding greengram even with the application of RDF alone and incorporating the stubbles of sweet corn along with root biomass. This might be attributed to application of MM₂ resulted in scorching effect in previous crop i.e., sweet corn which affected the normal growth and development of sweet corn even with the sufficient nutrient availability (Mahesh, 2020). In turn, these left over nutrients was available for succeeding greengram which increased the uptake of nutrients resulting in improved growth and yield of greengram. Additionally, stubbles and root biomass which was incorporated into the soil after the harvest of sweet corn which undergoes decomposition and releases nutrients in a synchronized manner with the crop growth stages of greengram, thus there is enhanced soil fertility leading to improved nutrient uptake and dry matter production of greengram ultimately resulting in higher growth and yield parameters in greengram (Imade, 2014; Mansuri, 2016; Patel et al., 2018; and Kantwa et al., 2024).
 
Yield attributes
 
The foliar application of a micronutrients mixture resulted in a significant increase in the number of seeds pod^-1, the number of effective nodules plant^-1 and the seed yield in the subsequent greengram crop (Table 3). The pooled data revealed that the foliar application of MM₂ (0.2%) + Humic acid @ 0.5% recorded maximum number of seeds pod^-1 (10.57), number of effective nodules plant^-1 (30.75) and seed yield (996 kg ha^-1) which was significantly superior over rest of the treatments. The lowest number of seeds pod^-1 (7.06), number of effective nodules plant^-1 (13.79) and seed yield (398 kg ha^-1) were also observed in absolute control.



Sowing greengram as a sequential crop after incorporating the stubbles of sweet corn after its harvest, coupled with the application of the recommended dose of fertilizers, can significantly enhance yield and yield parameters. The residual nutrients from the sweet corn crop, particularly nitrogen, can improve the number of seeds per pod due to better nutrient availability and improved soil structure left by the sweet corn stubbles. The number of effective nodules per plant is likely to be higher, facilitating better nitrogen fixation and overall plant vigour. This, in turn, can boost test weight as the seeds develop more robustly. Significantly higher seed and haulm yield was ascribed to the combined effect of better growth conditions and effective nutrient uptake resulting in improved biological yield. Similar results reported earlier by Gawai and Pawar (2006) and Devi et al., (2024).
 
Available soil micronutrients after harvest of sweet corn
 
Although micronutrients were not given through soil, to check the impact of foliar application of micronutrients mixture on soil micronutrient status, soils were analyzed for micronutrient content and when analyzed statistically, it was found non significant (Table 4). However, numerically highest soil micronutrients viz., Fe, Zn, Mn, Cu and B (11.99, 2.84, 8.85, 0.23 and 0.55 mg kg^-1, respectively) was recorded under the foliar application of MM₂ (0.2%) sprayed at 30 DAS. Whereas, absolute control registered lower soil micronutrients (8.94, 2.29, 6.80, 0.19 and 0.48 mg kg^-1, respectively).


 
Micronutrient content in stover of sweet corn
 
The data pertaining to the micronutrient content in stover of sweet corn as affected by foliar application of micronutrients mixture are presented in Table 5. Significantly higher iron, zinc, manganese, copper and boron content (83.53, 18.88, 29.09, 3.47 and 2.26 mg kg^-1, respectively) was recorded with the foliar application of MM₁ (0.1%) combined with humic acid @ 0.5% sprayed at 30 DAS and lower micronutrient content was observed in absolute control (61.66, 12.02, 22.05, 2.69 and 1.72 mg kg^-1, respectively).



The foliar application is a more efficient and effective approach which helps to improve micronutrient uptake by plants. Similar conclusion was also drawn by Piri (2012) and Balbaa and Awad (2013).
 
Economics
 
The pooled data in Table 6 revealed that the foliar application of MM2 (0.2%) + Humic acid @ 0.5% (T₇) gave the highest gross returns (Rs. 75,871 ha^-1), net returns (Rs. 45,203 ha^-1) and B:C ratio (2.47), respectively followed by the treatment T₇ (Rs. 71,369 ha^-1), (Rs. 40,700 ha^-1) and (2.33). The absolute control (T₁) produced the lowest gross returns (Rs. 30,512 ha^-1), net return (Rs. 6008 ha^-1) and a B:C ratio of (1.25). Higher net returns and a better B:C ratio might have been caused by the production of more yield in combination with a higher market price for greengram seeds. The outcome of Kamanga et al., (2010) is consistent with the outcomes of this study.

Residual effect of treatments on growing succeeding greengram without fertilization after sweet corn grown with foliar application of MM₂ (0.2%) + Humic acid @ 0.5% secured highest number of branches plant^-1, dry matter accumulation, number of seeds pod^-1, number of effective nodules plant^-1, seed yield, net return and B:C ratio in greengram on sandy loam soil. Thus, reported the promising residual effect on productivity and profitability of succeeding greengram in sweet corn - greengram cropping sequence.
 

All authors declare that they have no conflicts of interest.