Beetroot and radish production under different doses of green manures

Green manuring with spontaneous species from Caatinga biome has become an important strategy in production vegetables. One of the great challenges in tuberous vegetables production is to define an optimized quantity that provides a high productive yield with economic efficiency of production system. The objective of this study was to optimize agronomically and economically the production and its components of tuberous crops of beetroot and radish when manured with different amounts of green manures biomass, Merremia aegyptia and Calotropis procera from Caatinga biome, in two cropping seasons. The experimental design was a randomized complete block with five treatments and five replications. Treatments consisted of green manures amounts (16, 26, 36, 46, 56 t ha). The maximum agronomic efficiency of beetroot and radish was obtained with incorporation of 49.87 and 39.43 t ha -1 of M. aegyptia and C. procera, respectively, and the production maximum economic efficiency was reached when 36.14 and 36.48 t ha, respectively, of biomass of these green manures were added to the soil. The returns rate obtained in Research, Society and Development, v. 10, n. 16, e66101623205, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23205 2 beetroot and radish cultivation using the manures optimized amounts were 1.42 and 1.32 reais obtained for each real invested in the production of these tuberous.


Introduction
In Brazil, the area planted with beet is 18,000 hectares , and with radish is not very expressive, planted mainly in the green belts of the large cities, with production in 2017 of 14,937 and 118 t, respectively for beet and radish (IBGE, 2021). The production costs in 2017 were 13,850.00 R$ ha -1 for beet and 17,472.94 R$ ha -1 for radish (EMATER-DF, 2021), and their mean productivities are 40.94 and 16.60 t ha -1 for beetroot and radish (Martins et al., 2017;Aguiar et al., 2021). The correct use of fertilization corrects the soil deficiency and provides nutrients for plants (Batista et al., 2016).
Chemical fertilization and with animal manure are techniques commonly used in the vegetables production (Souza, 2018). But, as these inputs are expensive, producers have opted for the use of green manures. However, there is a lack of technical information on the use of these manures in vegetable production systems, especially in the Brazilian semi-arid region.
An alternative in the cultivation of tuberous crops in a semi-arid environment has been the use of spontaneously growing species that are easily available in the region's biome .
Some species of the Caatinga biome are alternatives for fertilizing vegetables, due to their qualities as "good fertilizers". They provide nutrients, and have excellent biomass with low C/N ratio, which provides faster decomposition and release of nutrients for the plants . Hairy woodrose can produce 36 t ha -1 of green biomass containing on dry basis 2.62% N, 0.17% P, 1.20% K, 0.90 Ca and 1.08 Mg. The roostertree can produce 51 t ha -1 of green biomass containing on dry basis 1.53% N, 4.0% P, 1.57% K, 0.93% Ca and 0.73 % of Mg .
Among these species are Merremia aegyptia and the Calotropis procera. There are few works with these species, but they show positive results in terms of increased productivity. Bezerra , using C. procera in the fertilization of carrot and cowpea intercropping, obtained a productivity of 17.31 t ha -1 and 1.29 t ha -1 for carrot and cowpea beans, respectively, by using 48.05 and 45.51 t ha -1 of C. procera, respectively. In turn, Silva et al. (2020), also working with carrot and cowpea intercropping fertilized with M. aegyptia, obtained a productivity of commercial roots of 29.47 t ha -1 and productivity of green grains of 3.13 t ha -1 using 32.69 and 50.17 t ha -1 of M. aegyptia, respectively.
The main problem surrounding the use of these species as green manure is to obtain quantities that optimize the production and its components of the tuberous crops, in order to achieve the maximum agronomic and economic efficiency in their cultivation. The objective of this work was to optimize agronomically and economically the production and its components of the radish and beetroot cultures, manured with different green manures biomass amounts, Merremia aegyptia and Calotropis procera from Caatinga biome, in two cropping seasons.

Locations and environmental conditions
Experiments were conducted from August to September 2016 and 2018, at the Experimental Farm 'Rafael Fernandes' of Universidade Federal Rural do Semi-Árido (UFERSA), located in the district of Lagoinha, 20 km from the municipality of Mossoró, RN, in geographic coordinates 5 ° 03 '37 " S, 37 ° 23' 50" W, altitude of 80 m.
The region's climate according to the Köppen classification is (BSh), dry and very hot, with two seasons: a dry season, which usually occurs from June to January, and a rainy season from February to May (Beck et al., 2018). Climatic data during the experimental period are shown in Table 1 (INMET, 2019). The soils in the experimental areas are classified as vermeho-amarelo distrófico with sandy-loam texture (Santos et al., 2018). In each experimental area, soil samples of 0-20 cm surface layer were collected, and analysed some chemical chacteristics. The results of these analyses are shown in Table 2.  Research, Society andDevelopment, v. 10, n. 16, e66101623205, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23205

Experimental design and treatments
The experimental design used in both experiments of each crop was in complete randomized blocks, with five treatments and five repetitions. The treatments consisted of mixtures of equal amounts of Merremia aegyptia (Convolvulaceae) and Calotropis procera (Apocynaceae) biomass in the following amounts (16,26,36,46 and 56 t ha -1 on a dry basis). These quantities were defined based on the quantities tested in researches with carrot and beetroot carried out in a semiarid environment by Favacho et al. (2017) and Morais et al. (2018). A treatment without fertilization (control) was used in each experiment.
The total area of the experimental plots was 1.44 m² with a useful area of 0.80 m², containing 80 plants of beetroot or of radish in the spacing of 0.20 m x 0.05 m. Each experimental plot was formed of six rows, containing 24 plants per linear meter of beetroot or radish. The beetroot cultivar used in the experiment was 'Early Wonder', and the radish cultivar was 'Crimson Gigante'.

Experiments conducting and green manure
The soil preparation consisted of plowing and harrowing, followed by raising the beds with the aid of a backhoe.
The green manures (M. aegyptia and C. procera) were collected from native vegetation in several locations in the rural area of Mossoró, RN, before the beginning of their blooms. The plants were crushed in a conventional forage machine into pieces of two or three centimeters, which were dehydrated at room temperature until reaching a moisture content of 10% and then subjected to laboratory analysis, obtaining the following chemical compositions, shown in Table 3.  Irrigations were carried out daily using a micro sprinkler irrigation system, provided in two shifts, morning and afternoon, during the experiment period, with an 8 mm blade applied each day, in order to maintain the soil in its field capacity.
The plantings in the first and second season were carried out by direct sowing radish (06/20/2016) and beetroot (06/13/2016), leaving only one plant per hole. Manual weeding was carried out whenever necessary. The radish and beetroot were harvested at 29 and 70 DAS, respectively. In the second season, the same procedures were followed for the cultivation of the radish (08/15/2018) and beetroot (08/01/2018).

Evaluated parameter and economic efficiency indicators
In the radish culture, the following characteristics were evaluated: plant height (measured with a ruler, from the ground level to the highest leaf, values expressed in cm), number of leaves per plant (obtained by counting), DM of shoots and roots (obtained by weighing the leaves and roots, respectively, values expressed in t ha -1 ), total and commercial productivity, and scrap root productivity.
For the cultivation of beetroot, the following determinations were made: plant height, number of leaves per plant, DM of shoots and roots, total and commercial productivity, and classification according to root diameter (DR): extra (DR> 4 and <5 cm), extra A (DR≥5 and <6 cm), extra AA (DR≥6 and <7 cm) and great (DR> 7 cm); cracked, bruised, forked roots or roots smaller than 4 cm are classified as scrap .
The indicators of economic efficiency, gross and net income, rate of return and profitability index were determined in both cultures. Gross income (RB) was obtained by multiplying the production per hectare by the value of the product (R$ 1.53 kg -1 for beetroot and R$ 4.08 kg -1 for radish) paid to the producer at market level in the region in October 2016 and 2018, expressed in R$ ha -1 . Net income (RL) was calculated by the following expression: RL = RB -TC, where TC is the total cost of production, resulting from the sum of all expenses with inputs and labor in each treatment, also expressed in R$ ha -1 . The rate of return (TR) was obtained by the expression: TR = RB/TC. The profit margin was obtained from the ratio between RL and RB, expressed as percentage.

Statistical analysis
A joint analysis of variance covering the two cropping seasons was performed for beetroot and radish variables, using the Sisvar software (Ferreira, 2019). When a significant interaction between the amounts of the M. aegyptia and C. procera mixture and the cropping seasons was recorded, it was partitioned and a polynomial or exponential model response function was adjusted to each variable, using Systat Software, 2021, where the point of maximum physical (agronomic) or economic efficiency was estimated.
The response function was obtained based on the follo wing criteria: biological logic of the variable, significance of the mean square of the regression residue (MSRR), high determination coefficient (R 2 ) and significance of the parameters of the regression function. The F test at 5% probability was used to compare the average values between the cropping seasons, and between the average value of the maximum physical or economic efficiency and the average value of the control treatment that did not receive green manure.

Results and Discussion
The results of the analyses of variance for the beetroot agronomic characteristics and economic indicators are presented in Table 1. Significant interactions were detected between amounts of the Merremia aegyptia and Calotropis procera biomass and cropping seasons for the most of agronomic characteristics and all economic indicators evaluated in beetroot, except for the total and commercial productivity of roots, and the productivity of scrap roots (Table 4). * Means followed by the same small letter in the column and capital letter in the row do not differ by F test at the 5% probability. + Mean of manured treatments is significantly different from the control treatment mean by the F test at the 5% probability level.

Agronomic characteristics of beetroot culture
The total and commercial beet roots productivities increased with the increase in the amounts of M. aegyptia and C.
procera biomass incorporated into the soil, in a polynomial model, reaching the maximum values of 18.40 and 17.58 t ha -1 for amounts of 48.55 and 49.87 t ha -1 of green manures biomass ( Figure 1A). Partitioning the interactions that occurred in the productivity of scrap roots and in the dry mass of beet roots, it was observed that there was a decrease in these characteristics with the increase in the green manures biomass amount incorporated in the soil, in exponential or polynomial model. The maximum values of scrap roots productivity of 1.38 and 0.96 t ha -1 was obtained in the first and second cropping season, respectively, in the green manures amount of 16.00 t ha -1 , according to equations shown in the Figure 1B. On the other hand, the optimized productivity of scrap roots of 1.14 t ha -1 was observed in the green manures amount of 16.00 t ha -1 ( Figure 1B). Research, Society and Development, v. 10, n. 16, e66101623205, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23205 Morais et al. (2019) studying beetroot intercropping with cowpea fertilized with spontaneous Caatinga species obtained total and commercial productivities of beet roots of 15.74 and 12.96 t ha -1 , respectively, when using amounts of C. procera biomass proceeding from 65 t ha -1 . These productivity values were lower than those obtained by beetroot in monocropping, which were 18.40 and 17.58 t ha -1 manured with the amounts of 48.55 and 49.87 t ha -1 of the green manures biomass, M. aegyptia and C. procera. These differences in productivity are due to the type of cultivation system used, which in the present study was monocropping. In terms of the amounts of green manures that obtained these productivities, they were also lower in monocropping than in intercropping.

Source: Authors
On the other hand, a decrease was registered in the productivity of extra and extra AA roots with an increase in the amounts of biomass of green manures, reaching a maximum value of 2.87 t ha -1 in the productivity of extra roots with 16 t ha -1 of green manures in the second season, and 3.02 t ha -1 in the productivity of roots extra AA in the first cropping season, also with 16.00 t ha -1 of the biomass (Figures 2A and 2C). The optimized productivities of extra A and extra AA roots in the two seasons grew with the amounts of green manures biomass, reaching maximum values of 2.59 and 4.31 t ha -1 with biomass amounts of 26.37 and 52.64 t ha -1 , respectively, while the optimized productivity of extra roots decreased with the quantities of green manures, reaching the maximum value of 1.67 t ha -1 with 16.00 t ha -1 of biomass ( Figures 2B, 2C and 2A).
The productivity of great roots increased with the increase of the amounts of biomass of M. aegyptia and C. procera  (Figures 2A, 2B and 2C), for that same root classification with the amounts of the biomass mixture of C. procera and M. aegyptia of 16; 26.37 and 49.51 t ha -1 . These differences between productivities are possibly due to the complementarity of the green manures, which provided better nutritional conditions for tuberoses and consequently a higher crop productivity.
The mean values of maximum physical efficiency (MPE) and of the treatments that received the M. aegyptia and C. procera manure (Tm) differed statistically from the values of the control (Tc) ( Table 4). In the production of dry masses of shoots and roots, these MPE values were 2.82 and 2.55 higher than the value of Tc, respectively.
In the productivity of total and commercial roots and in the classified productivity of great, extra A, extra AA and scrap roots, the MPE values were respectively 2.56; 2.29; 1.46; 1.44 and 2.77 higher than the value of the Tc. In the productivity of beetroot extra roots, the MPE value was 1.12 times lower than that of the control treatment.

Beetroot culture economic indicators
Significant interactions were also recorded between the factors, amounts of the biomass mixture of M. aegyptia and C. procera and cropping seasons for all economic indicators evaluated on beetroot ( Figure 3, Table 4). Source: Authors Research, Society andDevelopment, v. 10, n. 16, e66101623205, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23205 Partitioning the interactions between the factors, amounts of M. aegyptia and C. procera biomass and cropping seasons, an increase was observed in all economic indicators of beetroot, in the polynomial or exponential model, up to the maximum values of gross and net incomes, rate of return and profit margin of 28,545.39 and 11,202.16 Figures 3A, 3B, 3C and 3D).
Estimating the values of the maximum economic efficiency of the indicators over the cropping seasons, a behavior similar to those found within each growing season was also observed, with the values increasing up to a maximum of 26,942.76 and 7,380.83 R$ ha -1 ; 1.44 and 28.63% for M. aegyptia and C. procera biomass amounts of 51.28; 36.14; 27.60; 28.40 t ha -1 , then decreasing until the incorporation of the last amount of these green manures (Figure 3). The types of polynomial or exponential models tested in the characteristics of the beetroot fulfilled the selection criteria used to express the behavior of each evaluated characteristic. These were the biological logic (LB) of the variable, that is, when it turns out that after a certain dose of fertilizer there is no increase in productivity, the significance of the mean square of the regression residue (QMRR), a high value of the determination coefficient (R 2 ), the significance of the parameters of the regression equation, and the maximization of productivity and profit.
The mean values of maximum economic efficiency (MEE) and of treatments that received the M. aegyptia and C. procera manure (Tm) differed statistically from the values of the control (Tc) ( Table 5). For gross income, net income, rate of return and profit margin of beetroot, these MEE values were 12.15; 41.65; 1.42 and 30.78 higher than the Tc value, respectively.

Agronomic characteristics of radish culture
The results of the analyses of variance for the radish agronomic characteristics and economic indicators are presented in Table 5. Significant interactions were recorded between the amounts of the biomass mixture of M. aegyptia and C. procera and the cropping seasons for the most agronomic characteristics evaluated in the radish, except for the productivity of scrap roots (Table 5). Table 5. Mean values for the control (Tc), the treatment of maximum physical or economic efficiency (MPE or MEE) and of the manured treatments (Tm) in the dry masses of shoots and roots, total and commercial productivities of roots, productivity of scrap roots, gross income, net income, rate of return and profit margin in the radish culture manured with M. aegyptia and C. procera biomass in two cropping systems.

Comparison treatments
Dry mass of shoots (t ha -1 ) * Means followed by the same small letter in the column and capital letter in the row do not differ by F test at the 5% probability. + Mean of manured treatments is significantly different from the control treatment mean by the F test at the 5% probability level.
Partitioning the interactions that occurred in the dry masses of the shoots and roots and in the total and commercial productivities of radish roots, it was observed that there was an increase in these characteristics with the increase in the M.  procera biomass in two cropping seasons (CS1 and CS2). ** = P < 0.01; * = P < 0.05; OT = Optimized.
The productivity of scrap roots increased with the increase in the amounts of M. aegyptia and C. procera biomass incorporated into the soil, in the exponential model, reaching the maximum value of 0.60 t ha -1 for 52.99 t ha -1 of green manures biomass (Figure 4).
The mean values of maximum physical efficiency (MPE) and the treatments that received the M. aegyptia and C.
procera manure (Tm) differed statistically from the values of the control (Tc) in the production of dry masses of shoots and roots, in the total and commercial productivities of roots and in the productivity of scrap roots. These MPE values were 2.81; 1.86; 2.60; 2.79 and 1.56 higher than the value of Tc, respectively (Table 2).

Radish culture economic indicators
Regarding the economic indicators of the radish, there were significant interactions between the amounts of biomass mixtures of M. aegyptia and C. procera and the cropping seasons ( Figure 5, Table 5).  , then decreasing until the incorporation of the last quantity of these green manures ( Figure 5).
The mean values of maximum economic efficiency (MEE) and of the treatments that received the M. aegyptia and C.
procera manure (Tm) differed statistically from the values of the control (Tc) ( Table 5). For gross income, net income, rate of return, and the radish profit margin, these MEE values were 2.32; 16.40; 1.32 and 6.82 higher than the value of Tc, respectively.
The maximum physical efficiency (MPE) of the beetroot and radish treatments that received green manure were translated into economic terms in all the evaluated indicators, thus providing an optimized economic efficiency over the growing seasons (Tables 4 and 5). This behavior allows the beetroot grower to choose the optimum amount of green manure for incorporation and the economic indicator that best suits him in terms of productivity.
It is notable that the cultivation of beetroot and radish using a combination of two species of green manure provides a financial return that is compatible with the capital invested, thus becoming a viable alternative, especially for those small producers who do not have very high investment capital (Batista et al., 2016). In addition, it should be noted that spontaneous species for use in the manuring are readily available in the region.
The results obtained in these experiments are in agreement with those obtained by Silva et al. (2011) and Silva et al. (2019), working with the cultivation of beetroot in monocropping, as well as those obtained by Nunes et al. (2020) for radish monocropping.
The performance of the radish was similar to that of beetroot in terms of the regression models evaluated, where polynomial or exponential models were estimated to represent the agronomic and economic behavior of the performance of the characteristics evaluated in radish.
As in the culture of beetroot, the production of radish using two species of green manures provided good profitability, resulting in an economic return compatible with the capital invested, thus constituting a viable production alternative for tuberose vegetable producers.
The upward responses of the economic indicators evaluated in both tuberous crops in polynomial or exponential form and the economic optimizations as a function of the equitable amounts of the mixture of M. aegyptia and C. procera was because the tuberous crops responded very well to green manures. The environmental resources, provided by the quantities of the mixtures tested, were better used by beetroot and radish plants, whose use was translated into economic efficiency. Green manuring is known to improve fertility, increase organic matter content, decrease erosion rates, increase soil water retention and soil microbiota activity, increase nutrient availability, and reduce the amount of invasive plants (Pereira et al., 2016). Nunes et al. (2020), trying to optimize the radish productivity with applications of M. aegyptia in the semi-arid region of Rio Grande do Norte, obtained a commercial root productivity of 7.86 t ha -1 with an addition of 49.29 t ha -1 of this green manure, and an optimized maximum economic efficiency of 11,955.46 R$ ha -1 , when adding the dose of 46.00 t ha -1 of M.
aegyptia. In this research, a productive and economic efficiency of 6.21 t ha -1 and 8,857.20 R$ ha -1 was obtained with additions of 39.43 and 36.48 t ha -1 of the mixture of M. aegyptia and C. procera. This difference is due to the nutritional complementarity sponsored by the combination of green manures, which provides a satisfactory agronomic and economic efficiency and a decrease in the amount of green manures needing to be incorporated. Thus, these agroeconomic optimizations allow the producer of these tuberous cultures to decide on the recommendation of the amounts of the green manure mixtures of M. aegyptia and C. procera that best suits him in agronomic and economical terms.
Comparing the total yields of beet roots (18.40 t ha -1 ) and radish (7.47 t ha -1 ) fertilized with M. aegyptia and C.
procera obtained in this research with the average yields (40.94 and 16.60 t ha -1 ) of these tuberoses in the region, fertilized with chemical fertilizer, it was recorded that the yield of these crops obtained with green manures was about half of those obtained with chemical manure.

Conclusions
The maximum agronomic efficiency (commercial productivity) of beetroot and radish was possible with the incorporation of the doses of 49.87 and 39.43 t ha -1 of Merremia aegyptia and Calotropis procera, respectively, and the maximum economic efficiency of production of these tuberous vegetables was reached with the addition to the soil of 36.14 and 36.48 t ha -1 of the biomass of these green manures, respectively. The rates of return obtained in the cultivation of beetroot and radish with the optimized amounts of the manures combination were 1.42 and 1.32 reais obtained for each real invested in the production of these tuberous. The M. aegyptia and C. procera biomass use from Caatinga biome proved to be a viable technology for growers who practice the cultivation of beetroot and radish monocropping in semi-arid environment. This cultivation system should be recommended to family growers who produce tuberous vegetables in a sustainable form in semiarid ambient. Finally, there is an immediate need for investigate on the adequate management of production factors such as: organic fertilization type, mode and adequate time of application, as well as the ideal establishment of irrigation blade during the conduction of the cultures in the field.