Organic cabbage growth using green manure in pre-cultivation and organic top dressing fertilization

The experiment was conducted in (Integrated Agroecological Production System in Seropedica-RJ) Sistema Integrado de Produção Agroecológica (SIPA), Seropédica-RJ, to evaluate the effect of two maize populations in relation to baby corn productivity and shoot mass, to determine the contribution of pre-cultivated maize, green velvet and organic topdressing fertilization in the agronomic performance of cabbage (Brassica oleracea var. capitata). The experimental design consisted of randomized blocks with three treatments (maize population of 100,000 and 200,000 plants ha-1 and green velvet at 100,000 plants ha-1) and eight replicates. After that, cabbage was transplanted in the straw of these species, adopting a randomized block design allocated in split plots, totalizing six treatments, being three pre-cultivation practices and two organic topdressing fertilization doses (with or without 50 g fermented organic compost per planting hole). Considering “baby corn” productivity, no differences were observed compared to maize populations, with an average productivity of 822.5 kg ha-1. Green velvet pre-cultivation obtained the highest shoot dry mass (8.4 t ha-1). Cabbage crop was improved by green velvet pre-cultivation, reaching 60.7 t ha-1 and organic topdressing fertilization, reaching 60.4 t ha-1; however, in the presence of green velvet straw, topdressing fertilization did not promote additional yield benefit of this crop. Thus, we noticed that green manure using green velvet increased cabbage productivity, submitted to organic management, when compared to maize precultivation, making it able to replace organic topdressing fertilization.


Scientific communication
Hortic.bras., Brasília, v.36, n.4,October-December 2018 A strong appeal for sustainable agriculture has forced the search for new production systems, which include the replacement of synthetic fertilizers by organic ones.This practice promotes benefits to chemical, physical and biological soil characteristics, resulting in higher productivities (Sediyama et al., 2014).The evolution of the production process led to the substitution of agricultural management practices, in which plant and animal farms were integrated, for specialized systems.That is the reason why local availability of organic matter for fertilization had been reduced.
Alternatively to manures, the use of fermented "Bokashi" compost,
In tropical conditions, few scientific studies are related to the benefits of these fermented composts for plant mineral nutrition, though.Oliveira (2015) observed that the application of this compost resulted in an increase in number of leaves and fresh mass production of lettuce shoots (cv.Vera).
A n o t h e r a l t e r n a t i v e t o s o i l fertilization is the green manure.Silva et al. (2011b), studying succession of organic maize and kale cultivations under no-tillage system, verified that kale showed higher productivity, when intercropped with vegetables Crotalaria spectabilis and Mucuna deeringiana.Silva et al. (2011a) estimated that, in average, 67% of N in green velvet tissues is derived from the biological nitrogen fixation (BNF).
Using grass mulch has many advantages such as high capacity of mass production and nutrient cycling, mainly K. Decomposition of the mulching with grass straw is lower than the mulching with vegetables (Silva, 2002).The decomposition rate of straw, in general, is inversely proportional to the C/N ratio (Doneda, 2010), favoring the maintenance of mulching for a longer period of time.
Considering the maize shoot production, this species presents potential to be used as mulching.One alternative is producing straw and mini corn (baby corn) in situ.Baby corn is the female inflorescence harvested prior to fertilization (Barbosa, 2009), being processed as industrialized food, being source of additional cash income.Stigma (corn hair) is recommended by popular medicine to treat edema, cystitis, gout and kidney stones (Li & Yu, 2009).However, no results in relation to stigma production in maize fields in Brazil were found.
Many studies on management of Brassicacea in organic farming production have been carried out (Santos, 2009;Corrêa et al. 2014).This botanical family is a widely consumed food and has great socioeconomic importance (Filgueira, 2008) and also presents high nutrient extraction capacity (Silva et al., 2012).In conventional management, cabbage (Brassica oleracea var.capitata) is generally fertilized using high doses of soluble fertilizers (Aquino et al., 2005); however, in organic cultivation the green manure associated with organic fertilization provides good productivity levels for this vegetables (Pereira, 2007).
The aim of this study was to evaluate the effect of green manure, in precultivation with green velvet and corn in two population densities, associated with fermented organic compost "bokashi", on agronomic performance of cabbage submitted to organic cultivation.
Cover crops were sown on February 22, 2011.Maize, cultivar Eldorado, was grown in a 1.0-m spacing between furrows and 10 plants per linear meter (100,000 plants ha -1 ), 0.5 m between furrows and 10 plants per linear meter (200,000 plants ha -1 ).The green velvet (Mucuna pruriens cv.Utilis) was planted in 0.5-m spacing between furrows and 5 plants per linear meter (100,000 plants ha -1 ).The useful area consisted of 4 m 2 of central green velvet plots, for corn (100,000 plants ha -1 ) 2 central rows measuring 2 meters long were delimited and for maize (200,000 plants ha -1 ) 4 central rows measuring 2 meters long were delimited.
Baby corn ears were harvested between 56 and 75 days after sowing.
Those ears, measuring diameters from 0.8 to 1.8 cm (desired diameter) and with no deformations, were classified as marketable; the ones which were out of the desired diameter were classified as unmarketable (Pereira Filho & Cruz, 2001) and mini corn with deformations were classified as unmarketable due to deformation.After determining fresh mass, subsamples of baby corn and stigmas were taken to be dried in forced air circulation at 65°C for 72 hours.Then, dry mass was quantified, ground and taken to Laboratório de Química Agrícola of Embrapa Agrobiologia to determine N, P, K, Ca and Mg contents.
Cutting of corn and green velvet plants, in order to make straw mulch, was carried out during the green velvet flowering, at 144 days after sowing and kept on the soil.We quantified phytomass samples and took subsamples, then dry mass was quantified and macronutrients contents were analyzed, as it was done for baby corn.
Non-leguminous species were used as reference for natural abundance of 15 N in soil.False-milkweed (Emilia sonchifolia), wandering-jew (Commelina erecta) and maize (Zea mays) were collected in the experiment area and analyzed, showing the following δ 15 N values: 10.60; 9.32 and 8.06, respectively.The contribution of BNF was estimated using 15 N or δ 15 N abundance technique (Shearer & Kohl, 1988), with the aid of a mass spectrometer (Finnigan MAT, model Delta Plus).The percentage contribution of N derived from BNF was calculated using the formula: % BNF = 100 (δ 15 N of control plant -δ 15 N of fixing plant) / (δ 15 N of control plant -B), being B = -1.54,value corresponding to the isotopic discrimination of δ 15 N by Mucuna pruriens, according to that described by Okito et al. (2004), adopted to estimate all the other species.
Five days after the mulching species cutting, cabbage seedlings, cultivar Seicho, 32-day old, were transplanted into no-tillage system.The holes were arranged in double rows, spaced 0.4x0.3x0.7 m, totalizing 64 plants per subplot and were fertilized using planting fertilizer at a rate of 6.536 t ha -1 of tanned bovine manure presenting the following chemical analysis: 15.0; 3.5; 12.0; 14.4 and 6.2 g kg -1 , respectively of N, P, K, Ca and Mg.
The experiment design was in randomized blocks, with four replicates, arranged in split plot scheme, consisting of six treatments; plots consisted of three pre-cultivations (mulching species) and subplots with and without organic topdressing made from fermented compost (0 t ha -1 and 2.28 t ha -1 , and the last dose equivalent to 100.0 kg ha -1 N).This compost was prepared using a mixture of wheat bran (60%) and castor cake (40%), 200 L of water, 2 L of effective microorganisms solution and 1.5 kg of crystal sugar; the compost was kept in plastic buckets and hermetically sealed and left to stand for 1 month for fermentation.Chemical analysis showed: 44.3; 4.2; 11.5; 3.3 and 3.5 g kg -1 , respectively N, P, K, Ca and Mg.
Cabbage harvest was performed on October 20, 2011, at 89 days after transplanting.The following agronomic traits were evaluated: whole plant fresh mass, head fresh mass, head weight.Then, subsamples of each subplot were taken.These subsamples have undergone the same steps cover crop mass has (as it was mentioned above), in order to determine dry mass and the chemical analysis of plant material.
The obtained results were submitted to statistical analysis using F test, with the aid of SAEG Program and Scott-Knott test at 5% significance level.

RESULTS AND DISCUSSION
No significant differences were observed for baby corn productivity in population densities from 100,000 to 200,000 plants ha -1 (Table 1).Average values for marketable baby corn productivity were 822.5 kg ha -1 .Similar values for mass of marketable fresh baby corn were found by Corrêa et al. (2014) in the same experimental area and by Jesus (2009) in the North Fluminense Region.
In relation to baby corn stigmas, the authors did not observe any significant difference between the two plant population densities (Table 1).The average productivity reached 66 kg ha -1 ; despite of the fact that yield was not high, the high monetary value added to this by-product of baby corn harvest should be highlighted.Experimental results on stigma production were not found in literature, so that no discussion in relation to productivity reached using the adopted organic management was possible.
Productivity of shoot dry mass of green velvet was superior and was different from shoot dry mass of maize (Table 2).Productivity of shoot dry mass equivalent to 6.0 t ha -1 is considered an appropriate amount of straw for mulching, in no-tillage system (Darolt, 1998), in tropical conditions.On the other hand, in the Atlantic forest biome, this shoot productivity cannot be found.
Shoot dry mass of green velvet in this study was higher than the one found by Silva et al. (2011a) in similar weather conditions.However, in spite of producing greater amount of shoot phytomass, equivalent to 8.4 t ha -1 , this leguminous plant has a low C/N ratio, decomposing faster.Oliveira et al. (2008), analyzing different mulching decomposition, observed that C/N ratios were lower in leguminous C. juncea, velvet bean (Mucuna pruriens) and gliricidia (Gliricidia sepium) comparing with sugar cane grass (bagasse) and Cameroon grass.Percentage value of dry mass remaining in grass was superior to leguminous plants, which showed low contents of remaining N, showing faster release of this nutrient.
The authors observed that the population density of 100,000 maize plants ha -1 was higher and different from the population density of 200,000 corn plants ha -1 when analyzing mass productivities of maize shoots.In the lowest population density, productivity was similar to the value found, in similar weather conditions, by Corrêa et al. (2014) with the same cultivar.The lowest productivity reached in the highest population density allowed to verify a possible occurrence of intraspecific competition (Table 2), which did not influence in baby corn productivity, since the ears were early-harvested.For Andrade et al. (1999), this crop show low plasticity of growth when compared to other species of Poaceae family, due to its limited capacity of leaf expansion and prolificity.This botanical family produces a mass with high quality and volume (Andreola et al., 2000) and usually presents a decomposition rate inversely proportional to its C/N ratio (Doneda, 2010), favoring the establishment of mulching.
S o m e s t u d i e s s u g g e s t t h a t the efficiency of grass cultivation intercropped with leguminous plants produces straw with C/N ratio intermediate to that of the species in isolated crops, resulting in the lowest decomposition rate in relation to the phytomass when using leguminous plants exclusively, favoring the maintenance of mulching longer and synchronizing the supply stages and increased demand for N by crops (Corrêa et al., 2014).
The amount of N, K, Ca and Mg accumulated in shoot area of organic management, pre-cultivation with green velvet shows potential to provide significant amount of N to reach productivity levels similar to the ones obtained under conventional management.
Evaluating N contents in cabbage heads (Table 3), the authors observed that in green velvet straw cultivation N content was higher, differing significantly from the other treatments.This is due to the fact that this species performs biological fixation with atmospheric N 2 fixing bacteria.
Using the results, the authors concluded that cabbage which had been organically cultivated, under notillage system using green velvet, in the absence of topdressing application, with fermented organic compost, did not show any mass productivity decrease when compared with organic fertilized treatment (Table 3).These results show the contribution of BNF through the use of green velvet, after straw decomposition, as an effective source of N supply for the crop.Thus, organic topdressing can be replaced by precultivation with this leguminous plant, showing advantage of soil protection and, also monetary-cost benefits.Thus, this system can be an alternative for organic production systems, in which the use of synthetic N fertilizers is not allowed, as well as in conventional production systems.
In this context, Pereira (2007) suggests replace supplementary organic fertilization by pre-cultivation with C. juncea, since the productivity of cabbage grown on the straw of this leguminous plant, without topdressing application, did not differ from the productivity of cabbage with poultry litter, 200 kg ha -1 N.
In relation to the amount of nutrients accumulated in cabbage shoots, the authors observed that the topdressing with fermented organic compost resulted in an increase of N, P, K and Ca (Figure 2) when compared to the absence of this organic fertilization.Similarly, Oliveira et al. (2003) reported that supplementary topdressing with poultry litter, in cabbage cultivation, provided an increase in nutrient accumulation in the shoot area.
The authors concluded that population density of 100,000 maize plants ha -1 provided the same productivity of baby corn fresh mass and maize stigma dry mass, as density of 200,000 maize plants ha -1 .However, in the lower population density, shoot productivity is higher than the productivity found in the higher density, making it the best alternative, considering productivity indexes, seed economy and ease of crop management.
Pre-cultivations with maize and green velvet resulted in high productivity of dry shoot phytomass, which shows that a strategy favoring the use of these species can provide the production of straw produced in situ aiming to cabbage minimal cultivation under organic production systems.
Productivity of cabbage on green velvet straw was higher than the productivity of cabbage grown on maize straw, considering that topdressing with the compost did not result in an additional gain in relation to this  vegetable yield, this system showed to be unnecessary.Even cabbage being cultivated on the maize straw showed satisfactory productivity, above national average, and increased in the presence of topdressing fertilization with the organic compost "bokashi" obtained from wheat fermentation and cake.

Figure 1 .
Figure 1.Accumulated amount of nutrients in shoots of cabbage, cultivated on the mulching straw; 1 Bars with the same letters do not differ among themselves by Scott-Knott test, 5% probability; M100 and M200= Maize grown in the population density of 100,000 and 200,000 plants ha -1 , respectively; MV100= Green velvet cultivated in the population density of 200,000 plants ha -1 .Seropédica, UFRRJ, 2011.

Table 1 .
Fresh and dry mass (kg ha -1 ) of marketable and non-marketable husked baby corn per diameter and by deformations, dry straw mass and corn stigma dry mass, in two corn population densities.Seropédica, UFRRJ, 2011.Averages followed by same letter in the column do not differ from each other by Scott-Knott test, 5% probability level; MDC= marketable husked baby corn; NCBCD= Non-marketable baby corn by diameter; MDNDef= Non-marketable husked baby corn, by deformations; EEC= Stigmas of harvested ears; M100 and M200= Respectively, maize grown in the density population of 100,000 and 200,000 plants ha -1 .