Biological and economic efficacy of cowpea-radish association fertilized with organic manure in diverse planting arrangements

Green manuring and the spatial arrangement of planting intercropped crops are manageable factors to increase the bioeconomic effectiveness of intercropped systems. Therefore, the object of this study was to work out the bioeconomic efficacy in cowpea-radish association under diverse Calotropis procera biomass amounts and planting arrangements in two cultivation seasons through biological and economic indices. The research was conducted in a design of randomized complete blocks with four repetitions. The treatments were made of combination of four C. procera biomass amounts placed into the soil (20, 35, 50 and 65 t ha) with three cowpea-radish planting Research, Society and Development, v. 10, n. 11, e133101119298, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i11.19298 2 arrangements (2:2, 3:3 and 4:4). The biological indices, land equivalent ratio (LER), area-time equivalency ratio (ATER), actual yield loss (AYL), and system productivity index (SPI) and the economic indicators gross revenue (GR), net revenue (NR), rate of return (RR) and profit margin (PM) were evaluated to express the bio-economic efficacy of the cowpea-radish association. The greatest biological efficiencies of the cowpea-radish association were attained with LER and ATER of 1.75 and 1.25; AYL and SPI of 1.48 and 13.15 t ha, respectively, in the amount of 62 t ha of C. procera biomass in the planting arrangements 2: 2 and 3: 3. The largest net economic revenue (NR) of 16,382.85 R$ ha was attained in the amount of 52 t ha of C. procera in the planting arrangement 3: 3.

arrangements (2:2, 3:3 and 4:4). The biological indices, land equivalent ratio (LER), area-time equivalency ratio (ATER), actual yield loss (AYL), and system productivity index (SPI) and the economic indicators gross revenue (GR), net revenue (NR), rate of return (RR) and profit margin (PM) were evaluated to express the bio-economic efficacy of the cowpea-radish association. The greatest biological efficiencies of the cowpea-radish association were attained with LER and ATER of 1.75 and 1.25; AYL and SPI of 1.48 and 13.15 t ha -1 , respectively, in the amount of 62 t ha -1 of C. procera biomass in the planting arrangements 2: 2 and 3: 3. The largest net economic revenue (NR) of 16,382.85 R$ ha -1 was attained in the amount of 52 t ha -1 of C. procera in the planting arrangement 3: 3. Keywords: Vigna unguiculata; Raphanus sativus; Calotropis procera; Biological índices; Economic indicators.

Introduction
Association of cowpea [Vigna unguiculata L. (Walp.)] with radish (Raphanus sativus L.) is beginning to be practiced in the northeast of Brazil (Pereira et al., 2016). These two crops are considered two companion crops of economic and nutritional value that can complement each other in an intercrop (Chaves et al., 2020). When associated they can increase the total yield per unit of land and of time, increase the diversity of products, reduce the economic risks of the producer and help to use the land, labor and other environmental recourses of the rural land efficiently and judiciously (Nunes et al., 2018).
The intercrop with these two crops has not been investigated in regard to the management factors green fertilizing and planting arrangements of cultures. The green manuring practice can provide a lot of benefits for improving the bio-economic efficacy of intercrops. It increases the organic matter quantity and provides higher nutrients availability; provides higher effective cation exchange capacity of soil; decreases the Al contents exchangeable for its complexation; and increases the capacity of recycling and mobilization of leached or poorly soluble nutrients that are in the deepest layers of the profile (Valadares et al., 2016).
Planting arrangement as a management factor in intercrops can be manipulated to enhance the usage of ambient recources and efficiency of these associations, thus defining the pattern of plants distribution in the soil, determining the area shape available for each plant individually. Thus, it constitutes an important production factor in the competition between crops, consequently, in the bio-agronomic efficacy of the intercrops (Chaves et al., 2020). Intra and interspecific competition in the intercrop is established by the plants disposition and by the spacing between and within planting lines. When the competition starts, the plants distribution pattern regarding the soil is defined and the area available for each individual plant in the usage of ambient recources is determined. Therefore, to maximize the crops yield in intercrop, competition between and/or within the intercropped crops must be reduced, organizing them so that they can better use ambient recourses, and thus increase production and improve product quality (Schons et al., 2009). Researching the planting arrangements effect on cowpea-carrot intercrops in northeastern Brazil, Favacho et al. (2017), observed that planting arrangement 2: 2 provided greater producing and economic efficacy of intercrops.
Conversely, researching the planting arrangements effect (2: 2, 3: 3 and 4: 4) in the beet intercrop with two successive lettuce crops in a semiarid environment, Silva et al. (2018) did not observe effect of these planting arrangements on production and economic efficacy of the intercrops.
Thus, the object of this study was to work out the cowpea-radish intercrop bio-economic efficacy under different C. procera biomass amounts in diverse planting arrangements in two cultivation seasons.

Methodology
In the field experiments, it followed the Bhatt (2011)

Locales, weather and soils
The The soils of these sites were a typical Dystrophic Red Argisol , whose chemical analysis results are exposed in Table 1.

Experimental layout and treatment
The research was conducted in a randomized blocks design with four repetitions. The treatments were made of combination of four C. procera biomass amounts placed into the soil (20, 35, 50 and 65 t ha -1 ) with three planting arrangements of cowpea-radish (2:2, 3:3 and 4:4) in two cultivation seasons, 2015 and 2017.
The intercrops were performed with the cultures alternate-strips, with 50% of planted area with radish and 50% with cowpea. Each plot was constituted by radish alternated-rows at the same number of cowpea rows, according to planting arrangement in study, edged by two radish rows bordering one side and two cowpea rows the other side, forming the lateral borders. The total plots areas in the planting arrangements 2:2, 3:3, and 4:4 were 2.40, 3.00, and 3.60 m², respectively, with

Culture management and practices
On the cropping sites, were accomplished in the soils plowing, harrowing, and beds lifting. After this, it was accomplished a solarization of 45 days on the beds with the purpose to reduce the soil phytopathogen population.
The green manure C. procera for fertilizing of the essays was harvest in sites nearby Mossoró city two months before crops planting of radish and cowpea. In the 2015 experiment, this material was collected on June 29 and in the 2017 experiment on June 19. After this, this material was crushed in small pieces of 2 or 3 centimeters where they put to dry up to get the humidity of 10%. Samples of these materials were sent to the laboratory for macro and micronutrients analyses whose results are in Table 2. This fertilizer was placed into the soil at 20 days before crops sowing, on August 8, 2015 and July 28, 2017 at 0-20 cm depth. Fertilizer incorporation in radish and cowpea monocrops was accomplished in the 18 and 59 t ha -1 amounts, respectively, build on previous researches conducted by Batista et al. (2013) and .
Daily irrigation was accomplished by micro-sprinkler in two turns to favoring soil microbial activity and mineralization process of the organic matter. The plantings of cowpea and radish crops were made on August 28, 2015 (first season) and August 18, 2017 (second season), in direct sowing at the depth of two centimeters. After the plants emergence of radish and cowpea, at 7 and 10 days, they were thinned, leaving a plant per hole. Hand weeding was made where necessary.
The radish was harvested at 30 days after sowing (DAS) on September 27, 2015 and on September 17, 2017, while cowpea was harvested in four passes through in the interval of 51-65 and 50-62 DAS, in cultivation years.

Evaluated indices and indicators
The bio-economic efficacy of cowpea-radish intercrops was computed by biological indices and economic indicators. The SPI main advantage is that it expressed in t ha -1 , that is, it standardizes the secondary crop productivity (cowpea) in respect of main crop (radish). This index also identifies the combination that uses growth resources more effectively and also characterizes the performance of productive stability.
e) The production total costs (TC) per hectare were quantified in each treatment. Based upon these values, the indicators NR, RR, and PM were determined.
f) GR was computed by multiplying the productivities values per hectare by current price paid to the farmer. g) NR of each treatment was obtained subtracting from GR per hectare, the production TC involved in obtaining the same.

Statistical analysis
The bio-economic indices were analyzed using univariate analysis of variance for a randomized block design, using the SISVAR program (Ferreira, 2011). After that, a combined analysis was accomplished for each indice or indicator over cultivation years of 2015 and 2017. F of Fisher and Tukey tests were used to compare years of cultivation and planting arrangements. A regression curve was estimated for each indice or indicator with the C. procera amounts, through Table Curve program (Systat Software, 2021). The response functions obtained were evaluated based on the following criteria: biological logic, significance of the mean square of the regression residual (QMRr), high value of the coefficient of determination (R 2 ) and significance of the regression parameters, using the t test to 5% probability level.

Results and Discussion
It was not observed interaction between C. procera amounts and planting arrangements for no biological index assessed (Table 3). However, an interaction was registered between these C. procera amounts and cultivation seasons for SPI (Table 3). Table 3. Land equivalent ratio (LER), area time equivalency ratio (ATER), actual yield loss (AYL) and system productivity index (SPI) of the cowpea-radish intercropping in response to Calotropis procera biomass amounts placed into the soil, planting arrangements and cultivation seasons. * Means followed by the same lowercase letter in the row or uppercase letter in the column do not differ by F test or Tukey, respectively, at 5% probability. Source: Authors SPI of the cultivation second season (S2) and of intercropped system (S) increased with C. procera amounts placed into the soil until the highest values of 18.80 and 13.15 t ha -1 in the amounts of 62.09 and 62.51 t ha -1 of green fertilizer, decreasing until the application of the last amount ( Figure 3D). This index in the first cultivation season (S1) only had an increase of 1.29 between the smaller and greater amount of applied green manure. Increase in this index in S1 and S2 suggests that the green fertilizer is an important factor in economic feasibility of the intercrops (Pinto et al., 2012). Conversely, the SPI mean values in S2 within C. procera amounts and within planting arrangements differed significantly from those of S1. These results are partly by cause of radish productivity in single crop in S2 that reached higher values (Table 3). to Calotropis procera biomass amounts and the system productivity index, SPI (D) of radish-cowpea intercrop in response to Calotropis procera biomass amounts placed into the soil and cultivation seasons (S1 and S2).

Source: Authors.
It was also not observed interaction between C. procera biomass amounts and cultivation seasons for LER, ATER, and AYL (Table 3). Although, LER, ATER and AYL increased with C. procera crescent amounts placed into the soil, until the highest values of 1.75, 1.25 and 1.48 in green fertilizer amounts of 59.97; 63.27 and 62.55 t ha -1 , then decreasing until the last amount ( Figures 3A, 3B and 3C).
Based upon in LER and ATER, it can infer that the monocropping would need 75% more area and 25% more areatime to produce the equivalent in the intercrop fertilized with C. procera in one hectare (Diniz et al., 2017;Gebru, 2015). Both indices can assess the biological benefits of an intercrop (Rana & Rana, 2011), and thus express whether the intercrop become economically viable and profitable to be implemented by farmers (Maduwanthi & Karunarathna, 2019).
The positive value for AYL indicates intercropping advantage and determines complementarity between cultures, thus expressing the grade of intra and interspecific competition by the ambient recources at the different cultivation seasons (Cecilio Filho et al., 2015).
Significant interactions were also recorded between cultivation seasons and planting arrangements for the indices LER, ATER, AYL and SPI (Table 3).
Studying the cultivation seasons within each arrangement was observed there were significant differences between SPI values. The values for S1 stood out from those of S2 in all planting arrangements (Table 3). Mean values for LER, ATER and AYL in S2 differed from those of S1 in the planting arrangement 2:2. Within 3: 3 and 4: 4 arrangements, LER and AYL means in S1 stood out from those of S2, while the ATER mean values showed opposite comportment of the LER and AYL within these planting arrangements.
Within S1, LER and AYL mean values in the 3: 3 and 4: 4 planting arrangements stood out from those in the 2: 2 planting arrangement. Within S2, mean values of LER and AYL were similar for planting arrangements. Within S1, ATER and SPI mean values had the same behavior as LER and AYL in S2. Conversely, within that same growing season, ATER and SPI average values in the 2: 2 planting arrangement stood out from those of 3: 3 and 4: 4 planting arrangements.
Significant interactions between cultivation seasons and C. procera biomass amounts in the GR, NR, RR and PM were observed (Table 4).  Figure 4A). Conversely, gross and net revenues in S1 only increased by about 17,106.61 and 6,968.72 R$ ha -1 between the lowest and highest amount of the fertilizer placed into the soil. can avoid problems in usage of ambient recources.
Studying the cultivation seasons within each C. procera biomass amount, they were observed that the mean values for GR, NR, RR, and PM in S2 stood out from those of S1 in the biomass amount of 20 t ha -1 of the green fertilizer. In the amounts of 35, 50 and 65 t ha -1 , there were no significant differences between mean values of economic indicators in the cultivation seasons (Table 4).
There were no significant differences between mean values for economic indicators in the planting arrangements of the cultures (Table 4).
Finally, values obtained in the biological indices agree with those reached in economic indicators. Thus, economic indicators values show that the intercrop as agricultural system is increasingly recognized as a farming practice for sustainable economic development in the family farming Bedoussac et al., 2015).

Conclusions
The cowpea-radish intercrop is highly viable, as it presents bio-economic and sustainable efficacy when properly fertilized with C. procera biomass and well managed in respect to its planting arrangement. The greatest biological efficiencies of the cowpea-radish association were attained with LER and ATER of 1.75 and 1.25; AYL and SPI of 1.48 and 13.15 t ha -1 , respectively, in the amount of 62 t ha -1 of C. procera biomass in the planting arrangements 2: 2 and 3: 3. The largest net economic return (NR) of 16,382.85 R$ ha -1 was attained in the amount of 52 t ha -1 of C. procera in the planting arrangement 3: 3. LER, ATER, AYL, SPI, GR, NR, RR, and PM indices assessed can help the farmer to make adequate decisions in the implantation of his intercropped production system concerning sustainability. For future research with intercrops of cowpea and tuberous vegetables, urges the urgent need to study the interactions between the following production factors: green manuring, cultures planting arrangement and plant population density besides the appropriate times to plant the cultures in intercrop.