Intensifying food–forage production on medium land in Assam through teosinte–ricebean intercropping, integrated nutrient management, and relay rapeseed

Introduction

Livestock production is an important component of smallholder farming systems in India, particularly in the northeastern region, where crop residues, green fodder, and livestock manure are closely integrated with crop production. However, the availability of cultivated forage remains inadequate in relation to livestock requirements. This shortage is aggravated by limited land resources, seasonal variation in forage supply, increasing competition between food and fodder crops, and the need to maintain household income from small holdings. Under these conditions, intensifying production through suitable food-forage cropping systems offers an opportunity to increase total output without requiring additional land. Food-forage systems can be intensified through both spatial and temporal diversification. Spatial diversification involves growing cereal and legume crops together, while temporal diversification involves growing successive crops within the same year. Intercropping cereals with legumes can improve land-use efficiency through differences in canopy structure, rooting pattern, nutrient requirement, and growth duration. A cereal component generally contributes high biomass production, whereas the legume component can improve forage protein content and contribute to biological nitrogen fixation. The productivity advantage of intercropping is commonly evaluated using the land equivalent ratio (LER), with values greater than one indicating that the intercrop uses land more efficiently than the corresponding sole crops [1,2] . Teosinte (Euchlaena mexicana Schrad.) is a fast-growing cereal forage crop with considerable biomass-producing ability and adaptability to warm, humid conditions. Ricebean (Vigna umbellata (Thunb.) Ohwi & Ohashi) is a forage legume that can complement cereal crops by contributing protein-rich biomass and improving the biological diversity of the cropping system. Earlier studies have demonstrated the potential of teosinte and legume mixtures, including teosinte-ricebean combinations, but the performance of an intercrop depends strongly on the relative proportion and spatial arrangement of the component crops. An inappropriate row ratio may intensify interspecific competition, reduce the yield of one component, and weaken the residual benefits to subsequent crops. Therefore, identifying a suitable row arrangement is essential for obtaining a balance between cereal forage production, legume contribution, total biomass, and subsequent crop performance. The nutrient-management strategy is equally important in an intensive food-forage sequence. Continuous removal of biomass can accelerate nutrient depletion, particularly when forage crops are harvested at an immature stage and large quantities of nutrients are removed from the field. Exclusive dependence on mineral fertilizers may sustain short-term productivity but may not adequately improve soil organic matter and nutrientretention capacity. Conversely, organic sources such as farmyard manure (FYM) and vermicompost release nutrients more gradually and can improve soil physical, chemical, and biological properties, but nutrient release may not coincide with the rapid nutrient demand of high-yielding forage crops. Integrated nutrient management (INM), which combines mineral fertilizers with organic nutrient sources, may therefore provide a more synchronized supply of nutrientsy while maintaining soil fertility [3,4] . The residual effects of nutrient management are particularly important in a multi-season system. In the medium-land situations of Assam, a summer forage crop may be followed by transplanted rice during the kharif season and a short-duration oilseed crop after rice. Rihcebean in the first crop may benefit the succeeding rice crop through biological nitrogen fixation, residue return, and improved nutrient cycling. Similarly, organic nutrient sources applied to the forage phase may continue to influence rice growth and the performance of a relay crop. A relay rapeseed crop established in standing rice can use residual soil moisture and nutrients while reducing the fallow period between rice and the next cropping season. However, the success of relay rapeseed depends on the fertility remaining after the preceding crops and on the ability of the entire system to maintain timely crop establishment. Assam has substantial potential for such intensified systems because rice is the dominant crop and many medium-land fields remain available for a pre-rice crop and a post-rice relay crop. Nevertheless, high rainfall, acidic sandy-loam soils, low to medium soil fertility, and limited access to costly external inputs create challenges for sustained production. A suitable system must therefore be evaluated using multiple criteria, including forage yield, grain and oilseed yield, land-use efficiency, nutrient uptake, residual soil fertility, economic return, and energy productivity. Assessment of individual crop yield alone may fail to identify the most appropriate system for farmers who depend simultaneously on food production, livestock feeding, and soil fertility maintenance.

The present study was conducted to evaluate an intensive foodforage cropping system comprising summer teosinte and ricebean, succeeding kharif rice, and relay rapeseed under the medium-land conditions of Assam. The specific objectives were to: (i) assess the growth, forage yield, quality of sole and intercropped teosinte and ricebean; (ii) determine the effects of row ratio and integrated nutrient management on succeeding rice; (iii) quantify residual effects on relay rapeseed grown without additional fertilizer; and (iv) compare the systems in terms of land equivalent ratio, green-forage-equivalent yield and economics. It was hypothesized that a suitable teosinte-ricebean row ratio combined with integrated application of mineral fertilizer and organic manure would improve total system productivity and enhance the residual fertility available to succeeding rice and relay rapeseed.

Materials and Methods

A two-year field experiment was conducted during 2016-17 and 2017-18 at the Instructional-cum-Research Farm of Assam Agricultural University, Jorhat. The summer phase used a splitplot design with three replications. Main plots contained sole teosinte, sole ricebean, teosinte + ricebean in a 3:2 row ratio, or teosinte + ricebean in a 3:3 row ratio. Subplots received: 100% recommended dose of fertilizer (RDF); 50% of nitrogen (N) through RDF + 50% N through farmyard manure (FYM); 50% N through RDF + 50% N through vermicompost (VC); or an organic treatment supplying 50% N through VC + 50% N through FYM. Rice was grown in the kharif season in a splitsplit arrangement with either a recommended integrated nutrient management (INM) package or the same package with 50% organic manure (OM). Rapeseed was broadcast as a relay crop after rice without additional fertilizer. Crop growth, forage yield and quality, rice and rapeseed performance, land equivalent ratio (LER), soil properties, economics, and energy indices were measured. Data were subjected to analysis of variance appropriate to the split-split-plot design, and treatment means were compared at P = 0.05.

Results and Discussion

Teosinte-Ricebean Intercropping Performance Plant height and dry matter accumulation: Sole teosinte and sole ricebean produced taller plants and greater per-plant dry matter than either intercropped combination, due to reduced inter-plant competition (Tables 12). Among intercrops, the 3:3 ratio outperformed 3:2 for both components. INM-wise, 50% N (RDF) + 50% N (VC) gave the best growth, followed by 50% N (RDF) + 50% N (FYM), RDF alone, and fully organic, reflecting the benefit of combining readily available and slowrelease nutrient sources.

Forage yield: Sole teosinte produced the highest green forage yield, recording 233.73 and 238.65 q ha -1 during 2016-17 and 2017-18, respectively. Among the intercrops, the 3:2 teosintericebean row ratio produced greater teosinte forage yield than the 3:3 ratio, with yields of 163.74 and 170.74 q ha -1 . In contrast, ricebean performed better in the 3:3 arrangement, producing 127.75 and 136.50 q ha -1 green forage compared with 98.73 and 111.03 q ha -1 in the 3:2 arrangement. Sole ricebean produced the highest ricebean forage yield, at 194.06 and 201.06 q ha -1 (Table 3).

Land equivalent ratio (LER):

Both intercropping ratios recorded LER > 1, confirming a land-use advantage (Table 2).

The 3:3 arrangement recorded the highest LER, with values of 1.37 and 1.40 in the two years, indicating a land-use advantage of 37-40% over sole cropping. The 3:2 arrangement also recorded LER values greater than one, but its performance was lower than that of the 3:3 system, due to more balanced use of light, space, moisture and nutrients between the cereal and legume. INM had no significant effect on LER, showing that cropping geometry, not nutrient source, drove the advantage -consistent with established intercropping theory [1,2] .

Competition indices:

Ricebean was the more competitive/dominant component in both ratios, shown by its positive aggressivity and competitive ratio > 1, especially under 3:2 (Table 4). Teosinte's competitive ratio stayed below 1 in both arrangements, indicating milder dominance under the more balanced 3:3 system. Residual Effects on Succeeding Rice Plant height and yield attributes: Rice grown after sole ricebean recorded the tallest plants, most panicles/m², and most grains and filled grains per panicle, followed by the 3:3 intercrop, the 3:2 intercrop, and sole teosinte (lowest) (Table 5), reflecting the residual nitrogen and improved soil fertility left by the legume [5,6] .

Grain yield, straw yield and harvest index: Grain and straw yield followed the same order: highest after sole ricebean (47.24-49.62 and 76.14-79.26 q ha -1 ), then the 3:3 intercrop, then 3:2, lowest after sole teosinte (Table 6), consistent with reported cereal-yield benefits after legumes [7,8,9] . Residually, 50% N (RDF) + 50% N through VC again gave the highest grain and straw yield, ahead of the FYM combination and inorganiconly treatment, due to vermicompost's slow nutrient release, improved P availability, and better soil water-holding capacity [10, 11, 12] . The recommended rice INM package outperformed the 50%-organic package, showing that adequate direct nutrition remains essential alongside residual benefit. Harvest index did not differ significantly across treatments.

Residual Effects of Cropping System and INM on Relay Rapeseed

Plant height: Plant height of rapeseed responded significantly to the residual effect of the preceding cropping system at both the 80 days-after-sowing (DAS) and at-harvest stages in both years (Table 7). Plots that had carried sole ricebean-rice in the previous season produced the tallest rapeseed plants (82.55 cm and 85.68 cm at harvest in 2016-17 and 2017-18, respectively), followed by the 3:3 teosinte + ricebean intercrop, while sole teosinte-rice left the shortest plants. Because ricebean is a legume, its residue and root biomass add fixed nitrogen and organic matter to the soil, and this carry-over nutrient pool, rather than any fresh input, appears to be what pushed vegetative growth of the following rapeseed ahead of the non-legume sequences.

A similar pattern held for the residual effect of integrated nutrient management: plant height was tallest where the preceding crop had received 50% N through RDF together with 50% N through vermicompost, closely followed by the FYMsubstituted treatment, and shortest under 100% inorganic fertilization (RDF alone). Organic amendments evidently leave behind more than just nutrientstheir slow mineralization and associated micronutrient supply continue to support crop growth well after the manure itself was applied to the previous crop.

The INM package carried to rice also left a significant residual imprint, with the recommended package producing taller rapeseed than the same package diluted with 50% organic matter, in both years. None of the two-or three-way interactions among cropping system, INM, and the INM package to rice were significant for plant height in either season, indicating that each factor exerted its residual influence largely independently of the others.

Siliquae per plant and seeds per siliqua: Yield-attributing characters followed the same broad trend as plant height. The number of siliquae per plant and seeds per siliqua were both significantly higher where rapeseed followed sole ricebean-rice, and lowest under sole teosinte-rice, in both years of the study (Table 7). Reproductive development appears to be shaped by the nitrogen economy the preceding crop leaves behind: a stronger residual nitrogen and organic-matter pool translates into more pods setting per plant and more seeds filling within each pod. Residual INM produced the same ranking seen for growth: the vermicompost-substituted treatment gave the highest siliquae/plant and seeds/siliqua (21.65 and 18.70 in 2016-17; 22.11 and 18.32 in 2017-18), ahead of the FYM-substituted treatment, while sole RDF gave the fewest of botha difference of roughly 55-60% between the best organicsubstituted treatment and inorganic-only fertilization. The recommended INM package carried to rice again outperformed its 50% organic-matter variant for both attributes in both years.

As with plant height, the C × M × I interaction was nonsignificant, so the residual gains from cropping system, INM, and the rice-level INM package are best read as additive rather than mutually dependent. Seed yield and stover yield: Seed yield of rapeseed mirrored the growth and yield-attribute trends closely (Table 8). Sole ricebean-rice gave the highest residual seed yield (3.34 q/ha in 2016-17 and 3.70 q/ha in 2017-18), an advantage of roughly 44% and 25% over sole teosinte-rice in the respective years, with the 3:3 teosinte + ricebean intercrop placed second. The legume component in the preceding sequence therefore does more than support its own productivitythe nitrogen it fixes, and the organic matter it returns to the soil, carry through rice and into the following rapeseed crop, lowering the fertilizer burden the rotation as a whole has to bear while still sustaining seed yield of the third crop in the sequence. Residual INM effects on seed yield followed the identical ranking recorded for the yield-attributing characters: 50% N of RDF substituted with vermicompost gave the highest seed yield in both years, followed by the FYM-substituted treatment, with sole RDF the lowest. Likewise, the recommended INM package to rice produced significantly higher residual seed yield of rapeseed than the same package with 50% organic matter. Stover yield tracked seed yield throughouthighest under sole ricebeanrice and the vermicompost-substituted, recommended-package treatments, lowest under sole teosinte-rice and RDF-only fertilization. None of the interaction effects reached significance for either seed or stover yield in either year.

Harvest index: Harvest index followed a comparable but flatter pattern than seed and stover yield: it differed significantly with cropping system, residual INM and the INM package to rice in both years, again favouring the sole ricebean-rice sequence, the vermicompost-substituted INM treatment, and the recommended INM package to rice, though the spread between the best and poorest treatments was narrower than for the yield components themselves, indicating that the residual inputs raised seed and stover yield roughly in step with one another rather than skewing partitioning strongly toward either sink.

Oil content and oil yield: Oil content of the seed itself proved far less responsive to residual treatment effects than the other characters examined. The preceding cropping system, the residual INM, and the INM package carried to rice all failed to produce a statistically significant difference in oil content in either year (Table 8), even though the numerical values still tracked the same direction as the other traitshighest under sole ricebean-rice and vermicompost substitution, lowest under sole teosinte-rice and RDF alone. Oil content behaves as a largely genotype-fixed trait that residual soil fertility can nudge only marginally. Oil yield, by contrast, is the arithmetic product of oil content and seed yield, and it inherited the significance of the seed-yield differences that drove it. Sole ricebean-rice gave the highest residual oil yield (103.53 kg/ha in 2016-17 and 114.31 kg/ha in 2017-18), and 50% N of RDF through vermicompost gave the highest oil yield among the INM treatments (104.99 kg/ha and 119.22 kg/ha), both significantly ahead of their respective lowest-yielding counterparts. The INM package to rice, however, did not significantly affect oil content or oil yield of rapeseed in either year, and no interaction among the three factors was significant for either traitso the oil-yield advantage carried over from a legume-based, organicallymanaged preceding system is essentially a seed-yield effect rather than a change in seed quality.

System Productivity and Economics of the Whole System System production (GFEY):

The teosinte + ricebean (3:3)rice-rapeseed sequence gave the highest green forage equivalent yield (859.19 and 901.79 q/ha), followed by sole ricebean-ricerapeseed, due to the added legume fodder component boosting biomass (Table 9). Among nutrient treatments, 50% N of RDF + 50% N through vermicompost gave the highest GFEY (891.42 and 958.10 q/ha), while the fully organic treatment gave the lowestshowing that a balanced inorganic-organic combination outperforms either extreme. The recommended INM package to rice also gave higher GFEY than its 50% organic-substituted version. Interaction effects were nonsignificant.

Economics: Among cropping systems, the highest cost of [13] on the higher economic efficiency of legume-based sequences over sole cereal-fodder systems.

Summary of Findings

The 3:2 arrangement maximized the teosinte component, whereas the 3:3 arrangement was the strongest overall intercrop: its LER was 1.37 in 2016 and 1.40 in 2017. The 3:3 system produced 859.19 and 901.79 q ha -1 green-forage-equivalent yield (GFEY) across the two years. Among nutrient treatments, 50% N through RDF + 50% N through VC consistently improved forage biomass, rice performance through residual effects, rapeseed yield and net return. Rice following sole ricebean yielded 47.24 and 49.62 q ha -1 , while the 3:3 intercrop was the strongest intercropping predecessor, producing 43.32 and 45.04 q ha -1 . Relay rapeseed following the sole ricebeanrice sequence yielded 3.34 and 3.70 q ha -1 ; the 3:3 intercrop-rice sequence yielded 3.04 and 3.34 q ha -1 . Across the complete system, sole ricebean-rice-rapeseed generated the highest net returns (Rs. 73, 896 and Rs. 80, 312 ha -1 ) and benefit-cost ratios (1.41 and 1.53), while the 3:3 intercrop produced the highest GFEY and the highest energy productivity ratio among the intercropping options. The strongest combined recommendation was 3:3 teosinte + ricebean, with 50% N from RDF + 50% N from VC in the forage phase, recommended INM in rice, and relay rapeseed on residual fertility.

Conclusion

For medium-land situations of Assam, a 3:3 teosinte-ricebean intercrop followed by rice and relay rapeseed can intensify food and forage output without sacrificing system-level productivity.

Integrating inorganic fertilizer with vermicompost was more reliable than either sole inorganic fertilizer or the fully organic combination tested. The results support a system-level approach in which forage, grain, oilseed, soil condition, profitability, and energy performance are optimized together rather than crop by crop.

Acknowledgement

AcknowledgementThe author(s) gratefully acknowledge the Department of Agronomy, Assam Agricultural University, Jorhat, for providing the experimental facilities used to conduct this study.

References

1. Willey RW. Intercropping-its importance and research needs. Part 1: Competition and yield advantages. Field Crop Abstracts. 1979;32:1-10.
2. Willey RW, Rao MR. A competitive ratio for quantifying competition between intercrops. Experimental Agriculture. 1980;16:117-125.
3. Banik P, Sharma RC. Effect of organic and inorganic sources of nutrients on the winter crops-rice cropping system in sub-humid tropics of India. Archives of Agronomy and Soil Science. 2009;55(3):285-294.
4. Gudadhe N, Dhonde MB, Hirwe NA. Effect of integrated nutrient management on soil properties under cottonchickpea cropping sequence in Vertisols of Deccan plateau of India. Indian Journal of Agricultural Research. 2015;49(3):207-214.
5. Hegde DM. Long-term sustainability of productivity in rice (Oryza sativa)-wheat (Triticum aestivum) system in subhumid ecosystem through integrated nutrient supply. Indian Journal of Agronomy. 1998;43:189-198.
6. Okonji CJ, Okeleye KA, Aderibigbe SG, Oyekanmi AA, Sakariyawo OS, Okelana MAO. Effect of cowpea residue incorporation and nitrogen application rates on the productivity of upland rice. World Journal of Agricultural Sciences. 2011;7(6):710-717.
7. Devkota KP, Yadav DN, Chaudhary NK, Dangol DR, Basnet KB. Influence of spring season crop residue on productivity of rice-wheat cropping system. Journal of the Institute of Agriculture and Animal Science. 2006;27:53-58.
8. Ghosh PK, Bandyopadhyay KK, Wanjari RH, Manna MC, Misra AK, Mohanty M, et al. Legume effect for enhancing productivity and nutrient use-efficiency in major cropping systems-an Indian perspective: a review. Journal of Sustainable Agriculture. 2007;30(1):59-86.
9. Hegde DM. Cropping systems research highlights. In: Coordinators report, 20th Workshop, Tamil Nadu Agricultural University, Coimbatore, 1-4 June 1992. Modipuram, Meerut, India; 1992. p. 21-22.
10. Banik P, Chakraborty A, Bagchi DK. Integrated nutrient management in rice and its effect on water use and moisture depletion pattern of following crops in rainfed areas. Indian Journal of Agricultural Science. 1997;66:298-301.
11. Banik P, Ghosal PK, Sasmal TK, Bhattacharya S, Sarkar BK, Bagchi DK. Effect of organic and inorganic nutrients for soil quality conservation and yield of rainfed low land rice in subtropical plateau region. Journal of Agronomy and Crop Science. 2006;192:331-343.
12. Chettri GB, Rai BB, Samiano AR. Effects of FYM supplement with N, P and K on grain yield of rice. International Rice Research News. 1988;13:17-28.
13. Basu B, Kundu CK, Mondal S, Bandopadhyay P, De DK. Evaluation of forage production potential of maize grown for baby corn and green cob under new alluvial zone of West Bengal. Indian Agriculturist. 2009;53(3-4):177-181.