Residual Effects of Red Gram [Cajanus cajan (L.) Millsp.] on Growth, Yield and Quality of Fodder Maize (Zea mays L.)

Crop residues generated after harvest of the economic produce are critical organic inputs available for recycling.  It is estimated that the average annual out turn of crop residues in agricultural fields amounts to 683 million tonnes in the country (TERI, 2020). Incorporation of the crop residues in soil is primarily a means to maintain soil organic matter that results in enhanced biological activity, physical properties and nutrient availability (Antil and Narwal, 2007). Among the agricultural residues, leguminous residues have greater nitrogen benefits and addition in soil reduces the need for mineral N fertilizer application by farmers (Svubure et al., 2010). Keeping this in view, an experiment was undertaken to assess the effect of incorporation of red gram residues raised under different agronomic practices on fodder maize cultivated as succeeding crop in the southern laterites of Thiruvananthapuram district, Kerala.

Quantum of residues produced and nutrient additions
 
The quantity of residues generated with the different agronomic practices adopted in the two varieties of red gram and the nutrients (N, P and K) accretion possible based on the nutrient contents in the residues are presented in Table 1. The amount of residues produced were significantly the highest (4.83 t ha^-1) in T₇ (v₂s₁n₁, Vamban (Rg) 3 + 40 cm x 20 cm + 40:80:40 kg NPK ha^-1), which was at par with that in treatment T₁ (v₁s₁n₁, APK 1 + 40 cm x 20 cm + 40:80:40 kg NPK ha^-1). Vamban (Rg) and APK 1 are short duration varieties (100 - 105, 95 - 105 days, respectively) with a yield potential ranging from 0.94 to 1.04 t ha^-1. It is reasoned that the better growth and biomass production with the closer spacing and the highest nutrient dose that ensured an adequate supply of the major nutrients were responsible for the superior dry matter production and hence residues available for incorporation. The higher plant population (12 plants m^-2) in the closer spacing of 40 cm x 20 cm ensured higher quantum of residues compared to the wider spacing (60 cm x 30 cm). Considering the nutrient contents in the residues, the nutrient accretions possible are estimated to range from 46.58 to 101.19 for N, 4.50 to 16.34 for P and 16.72 to 35.16 for K kg ha^-1.


 
Effect residue incorporation on soil properties
 
Dehydrogenase activity in soil is considered as an indication of the soil microbial activity (Gu et al., 2009). Monitoring the dehydrogenase activity during decomposition revealed an increase, irrespective of the treatments (Table 2) and the values were maximum at 60 DAI. The treatment T₁ (v₁s₁n₁) resulted in significantly the highest dehydrogenase activity at all stages of estimation, the value being 30.13 µ TPF g^-1 soil 24 hr^-1 at 60 DAI, on par with the treatment T₇ (v₂s₁n₁), 30.12 µ TPF g^-1 soil 24 hr^-1.



The soil chemical properties at the start of the experiment are depicted in Table 3. Perusal of the data reveal that the treatment T₁ recorded the significantly highest organic carbon and available N before sowing and T₇ resulted the significantly highest P and K. The treatment T₁ was at par with T₇. The results indicate that residue incorporation has significant effect on soil chemical properties. The mineralisation of crop residues results in increased NPK availability in soil (Abiven and Recous, 2007).
 


Growth and yield of fodder maize
 
The variations in plant height and fodder yield are presented in Table 4. Plants were significantly superior in height (198.00 cm), in T₁₃, (POP-100 per cent nutrient application), indicating the stimulative effect of the readily available nutrients from the chemical fertilizer sources. The shortest plants (156.33 cm) were observed in the absolute control plot in which nether residues nor manures were applied. Green fodder yields followed a similar trend as plant height. The highest green fodder yield and dry fodder yield was observed in POP recommendation (37. 25 and 12.07 t ha^-1 respectively) and the lowest in absolute control plot (19.67 and 6.13 t ha^-1 respectively). Among the residue incorporated treatments, T₇ (Vamban (Rg) 3 + 40 cm x 20 cm + 40:80:40 kg NPK ha^-1) resulted in significantly tallest plants (183.78 cm), highest green (33.61 t ha^-1) and dry (11.37 t ha^-1) fodder yield on par with treatment T₁ (APK 1 + 40 cm x 20 cm + 40:80:40 kg NPK ha^-1). The yields were 70.86 and 85.48 per cent higher than the absolute control.



Fodder maize in the control plants were the shortest and yields were the lowest bringing to focus that maize being a heavy feeder realizes green yields in accordance with the nutrient absorbed by the crop. Application of fertilizers (T₁₃) coupled with the soil contribution could assure the timely nutrient demand of the crop and hence ensured proper growth and yields. Although the soil nutrient status was lower (Table 3), the nutrients from the chemical fertilizers could supply the nutrient requirement of the crop. On the other hand, in the residue incorporated plots, maize grew on the nutrients added to the soil via the residues and the ease in availability was governed by the mineralisation and activity of soil microorganisms. The release of N through the N fixation and degeneration of root nodules also enhances the N status in soil. The variation in the performance among treatments involving residue incorporation may be ascribed to the quantum of residues generated in red gram and N fixed due to the treatment imposed during its cultivation and the subsequent decomposition. The initial soil nutrient status (Table 3) is a reflection of the treatment effects in red gram and it is evident that T₇ recorded the comparatively highest available N, significantly highest P and K that contributed to the better performance of the maize crop in this treatment. These results are in conformity with the findings of Arif et al. (2011).
 
Quality parameters
 
It is evident from the data in Table 4 that the protein content was significantly the highest in the treatment T₁₃, where nutrients were given externally as chemical fertilizers. Among the different residue incorporated treatments, T₇ resulted in highest protein content, which was at par with treatment T₁. The absolute control treatment recorded highest carbohydrate content (78.53%) and the significantly lowest was in T₁₃ (66.23%). Among the residue incorporated treatments, T₁₂ resulted in highest carbohydrate content (77.50%) and the treatment T₁ resulted the lowest (68.72%).

The differences in the amount of protein and carbohydrate were due to difference in N availability (Khan et al., 2014). Increased N availability through chemical fertilizer application and absorption by fodder maize under POP recommended treatment would have caused the higher protein content. In residue incorporation, the plausible reason would be the mineralization of crop residues in soil, resulting in nutrient transformations and their mobility into the plant system for a longer period. Similar results have been reported by Bakht et al. (2009) and Almaz et al.  (2017). 

The higher N status in plants would have encouraged catabolism of carbohydrates leading to the lower carbohydrate content in these treatments. Maize in the non manured plants were deprived of N as evidenced by the lowered protein contents resulting in a higher carbohydrate status. These results are in conformity with findings of Patel (2014) and Buso et al. (2016). Considering the quality, maize plants were nutritionally better with residue incorporation than fertilizer application.
 
Changes in soil nutrient status
 
The soil available NPK was found to decline from the status before fodder maize cultivation (Table 3). Perusal of the data revealed that the maximum content was recorded in treatment T₁₀ (168.67, 114.92 and 275.48 kg N, P and K ha^-1 respectively). The values were the lowest in the treatments T₆, T₉ and T₃ for available N, P and K respectively. The decline noticed in soil NPK status is undoubtedly due to the utilization by the crop for its growth and metabolic activities. Maize crop requires an adequate supply of nutrients particularly N, P and K for its optimum growth and yield (Agba and Long, 2005). Being a soil exhaustive crop, fodder maize can exploit the inherent fertility of the soil to meet its demands and this would have depleted the nutrient status. However, the fertility status in soil with residue incorporation could support the maize crop for satisfactory yields.

The residual effect of the red gram legume and fertilizer treatments in fodder maize was apparent from the results of the study. The direct effect of the legume coupled with the decomposition dynamics of the incorporated residues could raise the fertility status of the soil resulting in fodder yields, nearly 80-90 per cent that realized under the package of practice recommendation illustrating the scope for reducing the external nutrient inputs in the succeeding crops of red gram cultivation, in a cropping sequence.

The study brings to focus the residual effect of red gram with respect to residue incorporation and its potential for supporting growth and yields in the nutrient exhaustive maize crop. The yields realized were only 10.83 and 6.16 per cent lower indicating that with residue incorporation substantial portion of the chemical fertilizer needed for maize can be reduced. Among the treatments imposed in red gram, the residues realized with the variety Vamban (Rg) 3 or APK 1 planted at 40 cm x 20 cm and fertilized with 40:80:40 kg NPK ha^-1 was found to be superior. Taking into account the cost of chemical fertilizers and need for eco-friendly practices, red gram residues can be effectively utilized in cropping systems. Residue incorporation practice can save Rs 16720 ha^-1 (cost of FYM and chemical fertilizers) compared to PoP recommendation.