Influence of crop geometry on nutrient concentration and uptake in maize-legume intercropping in eastern India

Introduction

Maize (Zea mays L.) is one of the world's most important cereal crops, serving as a major source of food, feed and industrial raw material. However, sustaining maize productivity in the eastern Indo-Gangetic Plains remains challenging because of declining soil fertility, imbalanced fertilizer use, low nutrient-use efficiency and smallholder-dominated production systems (Begam et al., 2024) [1] . These challenges are further intensified by increasing climatic variability and rising input costs, necessitating the adoption of resource-efficient and sustainable cropping systems (Rani et al., 2022) [7] . Cereal-legume intercropping has emerged as an ecologically sound strategy for improving productivity while maintaining soil fertility (Talukdar et al., 2023) [10] . Complementary use of growth resources by cereals and legumes enhances the efficiency of light interception, water utilization and nutrient acquisition compared with sole cropping (Zheng et al., 2022) [13] . Legumes contribute biologically fixed nitrogen, improve rhizosphere processes and mobilize relatively less available nutrients, thereby increasing nutrient availability to the associated cereal crop (Schwerdtner and Spohn, 2021) [9] . These positive interactions frequently result in greater system productivity and improved nutrient-use efficiency while reducing dependence on synthetic fertilizers (Dong et al., 2022) [2] . Among the factors determining the success of maize-legume intercropping, crop geometry plays a pivotal role by regulating the spatial arrangement of component crops. Appropriate row arrangements modify canopy architecture, root distribution, interspecific competition for growth resources and efficient acquisition and utilization of nutrients (Raza et al., 2019) [8] . Nutrient concentration and nutrient uptake are key indicators for assessing the efficiency of resource utilization in intercropping systems (Yadav et al., 2022) [11] . Enhanced soil enzyme activities and greater nutrient cycling under maize-legume systems further contribute to improved nutrient availability and uptake (Zhao et al., 2022) [12] . Despite considerable research on maize-based intercropping, information on the influence of crop geometry on nutrient concentration and uptake in Eastern India remains limited. Understanding how different crop geometries influence nutrient accumulation in maize-legume systems is therefore essential for improving nutrient-use efficiency and sustainable crop production. The findings provide valuable insights for designing efficient maize-legume intercropping systems with optimized crop geometry that enhance nutrient-use efficiency under resource-constrained conditions in Eastern India.

Materials and Methods

The field experiment was conducted during the rainy (kharif) season of 2022 at the research farm ICAR-Indian Agricultural Research Institute, Jharkhand. The soil was sandy loam, acidic in reaction (pH 5.4) analysing less contents of organic (0.29%), microbial biomass carbon (138.32 µg MBC/g soil), dehydrogenase activity (27.57 µg TPF/g soil/ day), available nitrogen (128.4 kg/ha), available phosphorus (6.62 kg/ha), available potassium (135.8 kg/ ha), available sulphur (21.84 kg/ha), available zinc (0.73 kg/ha), available iron (11.29 mg/ kg), available copper (0.26 mg/kg) and available manganese (6.51 mg/kg). Nine 'Treatments' viz., T 1 :Pure stands of maize, T 2 :Pure stands of green gram, T 3 :Pure stands of cowpea, T 4: Additive stand (AS) of Maize + Green gram, T 5: Replacement stand-I (RS-I) of Maize + Green gram, T 6: Replacement stand-II (RS-II) of Maize + Green gram, T 7: Additive stand (AS) of Maize + Cowpea, T 8: Replacement stand-I (RS-I) of Maize + Cowpea and T 9: Replacement stand-II (RS-II) of Maize + Cowpea was laid out in a randomized complete block design in 5 replications. Treatment differences were compared at 5% level of significance (P<0.05) for deriving a logical inference of the study. Concentration and uptake of nitrogen, phosphorus, potassium, sulphur, iron, zinc, copper and manganese were also analyzed in grain and stover.

Nutrient concentration and uptake by crop Plant nutrient analysis Collection and preparation of plant samples

Grain and straw samples of individual treatment were dried in an oven at 60 to 70 ℃ till constant weight was obtained and ground to fine powder in stainless steel Willey mill. The powdered plant samples were used for nutrient analysis.

Nitrogen concentration and uptake

Nitrogen concentration in grain and straw was expressed in percentage and determined by modified Kjeldahl method (Prasad et al., 2006) [6] . Nitrogen uptake was calculated by using the following equations: N uptake (kg/ha) in grain/straw = [N% in grain or straw × grain or straw yield (kg/ha)] Total uptake of N (kg/ha) = N uptake in grain + N uptake in straw Phosphorus concentration and uptake Phosphorus concentration in grain and straw was determined by using the vanadomolybdophosphoric acid yellow colour method at 420 nm wavelength on a UV-VIS spectrophotometer (Jackson, 1973) [4] . Total phosphorus uptake (kg/ha) was calculated by multiplying P content with the dry matter yield. P uptake (kg/ha) in grain/straw = [P% in grain or straw × grain or straw yield (kg/ha)] Total uptake of P (kg/ha) = P uptake in grain + P uptake in straw Potassium concentration and uptake Potassium concentration in grain and straw was determined by flame photometer (Prasad et al., 2006) [6] . Potassium uptake was calculated by using the following expression: K uptake (kg/ha) in grain/straw = [K% in grain or straw × grain or straw yield (kg/ha)] Total uptake of K (kg/ha) = K uptake in grain + K uptake in straw Sulphur concentration and uptake Sulphur concentration in grain and straw was determined by spectrophotometer (Prasad et al., 2006) [6] . Sulphur uptake was calculated by using the following expression: S uptake (kg/ha) in grain/straw = [S% in grain or straw × grain or straw yield (kg/ha)] Total uptake of S (kg/ha) = S uptake in grain + S uptake in straw Zinc concentration and uptake Zinc concentration in grain and straw was determined by Atomic absorption spectrophotometer (Prasad et al., 2006) [6] . Zinc uptake was calculated by using the following expression:

Zn uptake (kg/ha) in grain/straw = [Zn (mg/kg) in grain or straw × grain or straw yield (kg/ha)] Total uptake of Zn (kg/ha) = Zn uptake in grain + Zn uptake in straw

Iron concentration and uptake

Iron concentration in grain and straw was determined by Atomic absorption spectrophotometer (Prasad et al., 2006) [6] . Iron uptake was calculated by using the following expression: Fe uptake (kg/ha) in grain/straw = [Fe (mg/kg) in grain or straw × grain or straw yield (kg/ha)] Total uptake of Fe (kg/ha) = Fe uptake in grain + Fe uptake in straw

Copper concentration and uptake

Copper concentration in grain and straw was determined by Atomic absorption spectrophotometer (Prasad et al., 2006) [6] .

Copper uptake was calculated by using the following expression:

Cu uptake (kg/ha) in grain/straw = [Cu (mg/kg) in grain or straw × grain or straw yield (kg/ha)] Total uptake of Cu (kg/ha) = Cu uptake in grain + Cu uptake in straw

Manganese concentration and uptake

Manganese concentration in grain and straw was determined by flame Atomic absorption spectrophotometer (Prasad et al., 2006) [6] . Manganese uptake was calculated by using the following expression:

Mn uptake (kg/ha) in grain/straw = [Mn (mg/kg) in grain or straw × grain or straw yield (kg/ha)] Total uptake of Mn (kg/ha) = Mn uptake in grain + Mn uptake in straw

Results and Discussion

Effect on Nutrient concentration Maize Results showed the grain nutrient concentration of maize was recorded highest in Maize + Cowpea (RS-II) stands analysing nitrogen concentration in grain (1.03%) and stover (0.35%); phosphorus concentration in grain (0.342%) and stover (0.201%); potassium concentration in grain (0.367%) and stover (1.068%); sulphur concentration in grain (0.098%) and stover (0.152%); zinc concentration in grain (22.8 mg/kg) and stover (38.8 mg/kg); iron concentration in grain (27.4 mg/kg) and stover (183.7 mg/kg); copper concentration in grain (2.2 mg/kg) and stover (8.7 mg/kg); manganese concentration in grain (3.3 mg/kg) and stover (33.9 mg/kg). The lowest values were estimated with pure stand of maize analysing nitrogen concentration in grain (0.94%) and stover (0.29%); phosphorus concentration in grain (0.319%%) and stover (0.132%); potassium concentration in grain (0.331%) and stover (0.982%); sulphur concentration in grain (0.081%) and stover (0.133%); zinc concentration in grain (22.0 mg/ kg) and stover (36.8 mg/ kg); iron concentration in grain (26.2 mg/ kg) and stover (161.5 mg/ kg); copper concentration in grain (1.8 mg/ kg) and stover (7.9 mg/kg); manganese concentration in grain (2.9 mg/kg) and stover (32.9 mg/kg). No significant differences were observed in nutrient concentrations between maize stover and grain, except for phosphorus concentration, which was significantly different in the maize stover (Table 1.). Maize-cowpea intercropping increased the amount of nutrients compared to monocrop of maize. Fan et al. (2020) [3] reported that cereal-legume intercropping could also constitute a natural biofortification method that may improve the nutritional composition of the component crops.

Green gram

Results showed the grain nutrient concentration of green gram was recorded highest in pure stand of green gram stands analysing nitrogen concentration in grain (3.49%) and stover (0.77%); phosphorus concentration in grain (0.75%) and stover (0.28%); potassium concentration in grain (1.37%) and stover (0.82%); sulphur concentration in grain (0.24%) and stover (0.55%); zinc concentration in grain (22.9 mg/kg) and stover (58.7 mg/kg); iron concentration in grain (55.4 mg/ kg) and stover (119.0 mg/ kg); copper concentration in grain (9.6 mg/ kg) and stover (34.0 mg/ kg); manganese concentration in grain (12.5 mg/kg) and stover (28.8 mg/kg). The lowest values were estimated with additive stand of maize + green gram analysing nitrogen concentration in grain (3.27%) and stover (0.66%); phosphorus concentration in grain (0.68%) and stover (0.22%); potassium concentration in grain (1.30%) and stover (0.74%); sulphur concentration in grain (0.22%) and stover (0.53%); zinc concentration in grain (21.5 mg/kg) and stover (57.2 mg/kg); iron concentration in grain (52.2 mg/ kg) and stover (116.4 mg/ kg); copper concentration in grain (9.3 mg/ kg) and stover (33.6 mg/ kg); manganese concentration in grain (11.7 mg/kg) and stover (27.5 mg/kg). No significant differences were observed in nutrient concentrations between green gram stover and grain, except for phosphorus concentration in grain and stover (Table 2.). Jensen et al. (2020) [5] repoted that the higher uptake of nutrients in legume intercropping systems might be due to the better availability and supply of N by the leguminous crops intercropped with maize. The incorporation of legumes in cropping systems improves the physico-chemico-biological properties, soil fertility and ameliorate the resource use efficiency.

Cowpea

Results showed the grain nutrient concentration of cowpea was recorded highest in pure stand of green gram stands analysing nitrogen concentration in grain (3.44%) and stover (0.44%); phosphorus concentration in grain (0.64%) and stover (0.27%); potassium concentration in grain (0.37%) and stover (0.18%); sulphur concentration in grain (0.24%) and stover (0.45%); zinc concentration in grain (22.9 mg/kg) and stover (48.7 mg/kg); iron concentration in grain (55.4 mg/ kg) and stover (88.9 mg/ kg); copper concentration in grain (9.6 mg/ kg) and stover (23.9 mg/ kg); manganese concentration in grain (12.5 mg/kg) and stover (18.8 mg/kg). The lowest values were estimated with additive stand of maize + green gram analysing nitrogen concentration in grain (3.18%) and stover (0.29%); phosphorus concentration in grain (0.49%) and stover (0.17%); potassium concentration in grain (0.26%) and stover (0.16%); sulphur concentration in grain (0.22%) and stover (0.43%); zinc concentration in grain (21.5 mg/kg) and stover (47.2 mg/kg); iron concentration in grain (52.2 mg/ kg) and stover (86.4 mg/ kg); copper concentration in grain (9.3 mg/ kg) and stover (22.6 mg/ kg); manganese concentration in grain (11.7mg/kg) and stover (17.5 mg/kg). No significant differences were observed in nutrient concentrations between cowpea stover and grain, except for phosphorus concentration in grain and stover (Table 3.). Enhanced nutrient uptake in maize-legume intercropping systems is primarily associated with complementary nutrient acquisition, biological nitrogen fixation, and improved rhizosphere interactions. The inclusion of legumes also promotes soil fertility by improving soil physical, chemical, and biological characteristics, resulting in greater nutrient-use efficiency and sustainable crop production (Yadav et al., 2022) [11] .

Effect on Nutrient uptake Maize

Significant variation in grain and stover yields were also different in nutrient acquisition among different stands. Grain and stover nitrogen (94.4 kg/ha), phosphorus (37.3 kg/ha), potassium (114.3 kg/ha), sulphur (18.7 kg/ha), zinc (495.7 g/ha), iron (1733.8 g/ha), copper (86.5 g/ha) and manganese (317.5 g/ha) uptakes were significantly higher in T 7 (Table 4.). The higher uptake of nutrients in legume intercropping systems might be attributed to the leguminous crops intercropped with maize. That might have activated microbial population in microbes of plant rhizosphere to mobilize the inherent P and K and nutrients increasing their availability and uptake by plants and by addition of organic matter in the form of leaf litter by legume components. But the uptake of these nutrients varied significantly. It was mainly due to variation in yield (grain and stover) in different intercropping systems in maize crop. Similar findings were reported by Raza et al. (2019) [8] .

Green gram

Grain and stover nitrogen (67.3 kg/ha), phosphorus (17.8 kg/ha), potassium (21.8 kg/ha), sulphur (15.4 kg/ha), zinc (194.2 g/ha), iron (405.0 g/ha), copper (107.5 g/ha) and manganese (97.0 g/ha) uptakes were significantly higher in T 2 (Table 5.). The variation in uptake was mainly due to variation in yield (grain and stover) in different intercropping systems in green gram crop. Similar findings were reported by Zheng et al. (2022) [13] .

Cowpea

Grain and stover nitrogen (57.4 kg/ha), phosphorus (16.1kg/ha), potassium (10.1 kg/ha), sulphur (16.5 kg/ha), zinc (174.4 g/ha), iron (335.6 g/ha), copper (83.4 g/ha) and manganese (72.1 g/ha) uptakes were significantly higher in T 3 (Table 6.). The variation in uptake was mainly due to variation in yield (grain and stover) in different intercropping systems in cowpea crop. Similar findings were reported by Yadav et al. (2022) [11] .

Conclusion

The present study demonstrated that crop geometry significantly influenced nutrient uptake in maize-legume intercropping systems under the eastern Indian conditions. Intercropping maize with cowpea, particularly under the Replacement Stand-II (RS-II) arrangement, enhanced the concentration and uptake of major nutrients (N, P, K and S) as well as micronutrients (Zn, Fe, Cu and Mn) in maize compared with sole maize. Although the highest nutrient concentration and uptake in green gram and cowpea were recorded under their respective sole cropping systems due to higher plant population, maize-cowpea intercropping exhibited superior nutrient acquisition by the maize component, reflecting efficient complementary resource use and improved rhizosphere interactions. Therefore, the maize + cowpea (RS-II) cropping geometry can be recommended as a sustainable intercropping strategy for improving nutrient-use efficiency and maintaining soil fertility in the resourceconstrained regions of Eastern India.

Acknowledgement

AcknowledgementThe authors gratefully acknowledge the facilities and technical support provided by the ICAR-Indian Agricultural Research Institute, Delhi and ICAR-Indian Agricultural Research Institute, Jharkhand.

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