ABSTRACT

The use of organic fertilizers can increase the production of forest species for the extraction of wood from monoculture stands or integrated systems. This study aimed to evaluate the effect of applying doses of sheep manure on the biometric traits of Mimosa caesalpiniifolia (‘sabiá’) in a silviculture system in an area previously occupied by native degraded pasture in an Albaquult. The experimental design was randomized blocks with four repetitions, with treatments corresponding to five doses of sheep manure per plant: 0, 2, 4, 8, and 12 kg in the first year, while in the second year the double of the doses (0, 4, 8, 16 and 32 kg per plant) were applied as topdressing under the canopy. The following biometric variables were evaluated: height (H); root collar diameter (RCD); diameter at breast height (DBH); above-ground dry weight (AGDW); accumulation of nutrients (aerial part); and soil fertility. The plants were responsive to the organic fertilization regarding the variables H, DBH, and AGDW. The sheep manure increased the mean values of pH, P, K, Ca, Mg, SB, CEC, BS, S-SO₄ ^2- and Zn, and reduced the potential acidity in the 0-0.20 m soil layer. The organic matter variable increased up to the dose of 13.70 kg per plant. The accumulation rates of macro and micronutrients in the ‘sabiá’ plants were N > Ca > K > Mg > P > S and Fe > Mn > B > Zn > Cu, respectively.

Key words:
organic fertilizers; soil fertility; semiarid region

RESUMO

O uso de adubos orgânicos pode incrementar a produção de espécies florestais, as quais podem ser usadas para extração de madeira em monocultivos ou em sistemas integrados. Objetivou-se neste estudo, avaliar a aplicação de doses de esterco de ovino na implantação de Mimosa caesalpiniifolia (sabiá) em sistema silviagrícola, de uma área anteriormente ocupada por pastagem degradada em um Albaquult (Planossolo Háplico). O delineamento experimental foi em blocos casualizados, com quatro repetições, e os tratamentos corresponderam às seguintes doses: 0, 2; 4; 8 e 12 kg de esterco de ovino por planta no primeiro ano, cujas quantidades empregadas foram reaplicadas em dobro (0, 4, 8, 16 e 32 kg por planta) no ano seguinte na projeção da copa. As variáveis avaliadas corresponderam aos atributos biométricos: altura (ALT); diâmetro do colmo ou coleto (DC) e diâmetro na altura do peito (DAP); massa seca da parte aérea (MSPA); acúmulo de nutrientes (parte aérea); e fertilidade do solo. As plantas de sabiá foram responsivas à adubação orgânica com incrementos nas variáveis ALT, DAP e MSPA. O esterco de ovino aumentou os valores médios na camada de 0-0,20 m para pH, P, K, Ca, Mg, SB, CTC, V, S-SO₄ ^2- e Zn; com diminuição da acidez potencial. Para a variável matéria orgânica o incremento ocorreu até à dose de 13,70 kg por planta. O acúmulo de macro e micronutrientes, em plantas de sabiá foi N > Ca > K > Mg > P > S e Fe > Mn > B > Zn > Cu, respectivamente.

Palavras-chave:
adubos orgânicos; fertilidade do solo; região semiárida

Introduction

The use of organic inputs is essential to assure the full development of perennial crops by acting as a source of nutrients, principally in areas with low soil fertility and/or small use of conventional fertilizers. Studies have shown that the long-term use of organic fertilizers improves soil fertility in semiarid regions (García-Orenes et al., 2016García-Orenes, F.; Roldán, A.; Morugán-Coronado, A.; Linares, C.; Cerdà, A.; Caravaca, F. Organic fertilization in traditional Mediterranean grapevine orhards mediates changes in soil microbial community structure and enhances soil fertility. Land Degradation & Development, v.27, p.1622-1628, 2016. https://doi.org/10.1002/ldr.2496
https://doi.org/10.1002/ldr.2496... ; Souza et al., 2016Souza, H. A. de; Melo, M. D.; Primo, A. A.; Vieira, L. V.; Pompeu, R. C. F. F.; Guedes, F. L.; Natale, W. Use of organic compost containing waste from small ruminants in corn production. Revista Brasileira de Ciência do Solo , v.40, p.1-16, 2016. https://doi.org/10.1590/18069657rbcs20150385
https://doi.org/10.1590/18069657rbcs2015... ).

Although the information is spotty about the general soil fertility in Brazil’s semiarid Northeast region, some studies have indicated that phosphorus and nitrogen are the main limiting elements for plant nutrition (Salcedo, 2006Salcedo, I. H. Biogeoquímica do fósforo em solos da região Semi-árida do NE do Brasil. Revista Geografia, v.23, p.159-184, 2006.; Menezes et al., 2012Menezes, R. S. C.; Sampaio, E. V. S. B.; Giongo, V.; Pérez-Marin, A. M. Biogeochemical cycling in terrestrial ecosystems of the Caatinga Biome. Brazilian Journal of Biology, v.72, p.643-653, 2012. https://doi.org/10.1590/S1519-69842012000400004
https://doi.org/10.1590/S1519-6984201200... ). On the other side, the continuous use of organic fertilizers could improve the concentration of P in soil, but the most important is the chemical form of P that comes from organic fertilizer (Komiyama & Ito, 2019Komiyama, T.; Ito, T. The caracteristics of phosphorus in animal manure composts. Soil Science and Plant Nutrition, v.65, p.281-288, 2019. https://doi.org/10.1080/00380768.2019.1615384
https://doi.org/10.1080/00380768.2019.16... ).

The manure of goats and sheep has larger concentrations of nitrogen, calcium, and manganese; specifically, sheep manure contains higher phosphorus and potassium concentrations than the manure from other animals, such as donkeys and cattle (Souto et al., 2005Souto, P. C.; Souto, J. S.; Santos, R. V.; Araújo, G. T.; Souto, L. S. Decomposição de estercos dispostos em diferentes profundidades em área degradada no semi-árido da Paraíba. Revista Brasileira de Ciência do Solo , v.29, p.125-130, 2005. https://doi.org/10.1590/S0100-06832005000100014
https://doi.org/10.1590/S0100-0683200500... ; 2013Souto, P. C.; Souto, J. S.; Nascimento, J. A. M. do. Liberação de nutrientes de estercos em Luvissolo no Semiárido paraibano. Revista Caatinga, v.26, p.69-78, 2013.).

Crops propagated from seedlings customarily receive more attention when employing organic fertilizers, principally because they exploit the same soil volume for the long-term, considering improving the physical and chemical properties (Rós et al., 2013Rós, A. B.; Hirata, A. C. S.; Narita, N. Produção de raízes de mandioca e propriedades químicas e físicas do solo em função de adubação com esterco de galinha. Pesquisa Agropecuária Tropical, v.43, p.247-254, 2013. https://doi.org/10.1590/S1983-40632013000300001
https://doi.org/10.1590/S1983-4063201300... ).

The nutritional state and nutrient cycling of ‘sabiá’ (Mimosa caesalpiniifolia) have been evaluated to produce seedlings, as well as fertilization in shrubland areas, and measurement of the production of leaf litter (Lacerda et al., 2006Lacerda, M. R. B.; Passos, M. A. A.; Rodrigues, J. J. V.; Barreto, L. P. Características físicas e químicas de substratos à base de pó de coco e resíduo de sisal para produção de mudas de sabiá (Mimosa caesalpiniaefolia Benth). Revista Árvore , v.30, p.163-170, 2006. https://doi.org/10.1590/S0100-67622006000200002
https://doi.org/10.1590/S0100-6762200600... ; Caldas et al., 2009Caldas, G. G.; Santos, M. V. F. dos; Ferreira, R. L. C.; Lira Júnior, M. de A.; Saraiva, F. M. Efeito da fertilização fosfatada na produção de raízes, liteira e nodulação de Mimosa caesalpiniifolia Benth. Revista Árvore, v.33, p.237-244, 2009. https://doi.org/10.1590/S0100-67622009000200005
https://doi.org/10.1590/S0100-6762200900... ; Freire et al., 2010Freire, J. de L.; Dubeux Júnior, J. C. B.; Lira, M. de A.; Ferreira, R. L. C.; Santos, M. V. F. dos; Freitas, E. V. de. Deposição e composição química de serapilheira em um bosque de sabiá. Revista Brasileira de Zootecnia, v.39, p.1650-1658, 2010. https://doi.org/10.1590/S1516-35982010000800005
https://doi.org/10.1590/S1516-3598201000... ).

Since organic fertilization improves the chemical properties of the soil, this study aimed to evaluate the effect of sheep manure doses on the biometric traits of ‘sabiá’ grown and the chemical attributes in an area previously occupied by native degraded pasture in an Albaquult located in a semiarid region of the state of Ceará, Brazil.

Material and Methods

The experiment was conducted from June 2014 to March 2016 on the Triunfo Farm in Ibaretama, Ceará, Brazil, in an Albaquults area. The soil was analyzed beforehand in the surface (0.0-0.2 m) and subsurface (0.2-0.4 m) layers (Table 1).

The variables P, K, Al, and OM had concentrations considered low, while Ca was medium and Mg high, according to the classification proposed by Fernandes (1993Fernandes, V. L. B. Recomendações de adubação de calagem e adubação para o Estado do Ceará. Fortaleza: Imprensa Universitária, 1993. 248p.). Thus, no lime was applied for pH correction. During the period of the experiment, it rained 1,207 mm. Figure 1 presents the monthly distribution of rainfall during the experimental period.

The experimental area was formerly used for extensive grazing of cattle and sheep and was mainly composed of native Caatinga pasture.

The experimental design was randomized blocks with five sheep manure doses and four repetitions, where the experimental unit was composed of six plants. The block was composed of each double row of ‘sabiá’, spaced to provide room for the cultivation of annual crops.

The seedlings were produced in a nursery installed at the Quixadá Campus of the Federal Institute of Education, Science, and Technology of Ceará (IFCE). They were transplanted in June 2014 into pits with dimensions of 0.4 x 0.4 x 0.4 m. At the time of planting, 2.0 L of hydrogel was applied per pit. The seedlings were planted with a spacing of 3.0 x 2.0 m in double rows, in turn, spaced 10 m apart, with annual crops (corn, millet, sunflower, cowpea) grown between the double rows in the agricultural years of 2015 and 2016.

The sheep manure was applied directly in the pits with doses of 0, 2, 4, 8 and 12 kg per pit (dry base) (June/2014). The sheep manure was obtained in the farm itself and presented the following chemical characteristics: N, P, K, Ca, Mg, S, Cu, Fe, Zn, Mn, B, cellulose, lignin, and pH_H20: 12.6 (g kg^-1), 3.2 (g kg^-1), 8.4 (g kg^-1), 16.6 (g kg^-1), 8.4 (g kg^-1), 3.1 (g kg^-1), 22 (mg kg^-1), 3920 (mg kg^-1), 91 (mg kg^-1), 550 (mg kg^-1), 18 (mg kg^-1), 95 (g kg^-1), 130 (g kg^-1), and 8.7, respectively.

After planting, the plants were irrigated manually with 10.0 L of water per plant per week until December 2014. The other crop managements/15, manure was applied as topdressing under the canopy projection, approximately 0.3 m from the trunk, at twice the initial doses: 0, 4, 8, 16, and 24 kg per plant (dry base). The total manure applied in 2014/2015 was: 0, 6, 12, 24, and 36 kg per plant (dry base).

The following agronomic variables were evaluated in two plants per plot (6 m² of useful area/plot), nine months after planting: height - H (cm) and root collar diameter - RCD (cm) measured at the height from 5 to 8 cm from the soil.

The same variables were measured 22 months after planting, along with diameter at breast height - DBH (cm) and above-ground dry weight - AGDW (grams per plant), in this case, based on one plant per plot. The dry weight was measured after drying the sample material in a forced-air oven at 60 ºC until reaching constant weight. The dried samples were then milled to analyze the macro (N, P, K, Ca, Mg and S) and micronutrients (B, Cu, Fe, Mn and Zn), as described by Miyazawa et al. (2009Miyazawa, M.; Pavan, M. A.; Muraoka, T.; Carmo, C. A. F. S. do; Melo, W. J. de. Análise química de tecido vegetal. In: Silva, F. C. Manual de análises químicas de solos, plantas e fertilizantes. Brasília: Embrapa Informática Tecnológica, 2009. p.191-233.). The data on nutrient concentrations and dry weight were used to calculate the accumulation of nutrients.

The soil fertility was analyzed in single samples (five per plot), in the 0-0.20 and 0.20-0.40 m layers under the canopy projection, always at the start of the rainy season. The samples were collected before fertilization, in 2015 and 2016, to evaluate the following variables: pH; organic matter (OM); phosphorus (P); potassium (K); calcium (Ca); magnesium (Mg); potential acidity (H+Al); sum of bases (SB); cation exchange capacity (CEC); base saturation (BS); sulfur (S-SO₄ ^{2 -}); sodium (Na); boron (B); copper (Cu); iron (Fe); manganese (Mn); and zinc (Zn), according to Donagemma et al. (2011Donagema, G. K.; Campos, D. V. B. de; Calderano, S. B.; Teixeira, W. G.; Viana, J. H. M. Manual de métodos de análise de solo. Rio de Janeiro: Embrapa Solos, 2011, 230p. Documentos, 132).

The data were submitted to analysis of variance using the SISVAR software (Ferreira, 2011Ferreira, D. F. Sisvar: A computer statistical analysis system. Ciência e Agrotecnologia, v.35, p.1.039-1.042, 2011. https://doi.org/10.1590/S1413-70542011000600001
https://doi.org/10.1590/S1413-7054201100... ) and regression analysis.

Results and Discussion

In the first year (2015), there were significant differences in the chemical attributes in the surface layer (0-0.20 m) for pH (p < 0.05) and Zn (p < 0.01); and in the subsurface layer (0.20 - 0.40 m) for pH (Table 2). In both layers, the pH increased with rising doses of sheep manure, as was also the case of zinc, but only in the surface layer (Table 3).

In the subsurface layer in the first evaluation year (2015), the pH increased with rising sheep manure doses in the pits, which can be related to the complexation of H⁺ ions.

In the second evaluation year (2016), in the surface layer, there were significant differences (p ≤ 0.01) due to organic fertilizer doses for most variables, except for Na and the micronutrients B, Cu, Fe, and Mn (Table 2). There were significant differences in the 0.20-0.40 m layer (p ≤ 0.01) only for P and Fe (Table 2).

In the surface layer, there was a linear increase with rising sheep manure doses for the variables pH, P, K, Ca, Mg, SB, CEC, BS, S-SO₄ ^2-, and Zn, and a decline of the concentrations for potential acidity in 2016. For organic matter (OM), the best response model was quadratic, with a maximum value at the dose of 13.7 kg per plant (Table 3).

In the subsurface layer, there was a linear increase in phosphorus concentration with rising manure doses. For Fe, the response was quadratic, with a maximum value at the manure dose of 9.9 kg ha^-1, followed by a decline in concentration after this dose (Table 3).

In the second evaluation (2016), the variables pH, Ca, and BS were still below the critical levels despite the increase of the averages compared to the previous year. The content of OM was below the value obtained in 2015, which can be possibly be explained by its mineralization. On the other hand, the average P, K, and Mg concentrations were above the critical levels.

Regarding agronomic evaluation, in the first year (2015), there were significant differences for the parameters height (H) and root collar diameter (RCD) according to the doses of organic fertilizer applied (Table 4). The doses of 7.1 and 6.5 kg of manure per pit increased the mean values of the two variables, respectively (Table 4).

In the second evaluation year (2016), the variables height (H), diameter at breast height (DBH), and above-ground dry weight (AGDW) differed according to the organic fertilizer doses, with linear increases with rising doses in all cases (Table 4). For this evaluation (2016), for each kilogram of manure applied, the AGDW increased by 7.05 g per plant (Figure 2).

The doses of manure applied caused differences in the contents of nutrients (Table 5), except for Cu, Fe, Mn, and Zn. The average values of content of macro and micronutrients in decreasing order were N > Ca > K > Mg > P > S and Fe > Mn > B > Zn > Cu, respectively.

The average values for pH, P, K, Ca, Mg, and BS in the surface layer obtained in 2015 were below the critical values for subsistence farming in smallholdings, as described by Souza et al. (2014Souza, H. A. de; Cavalcante, A. C. R.; Tonucci, R. G.; Pompeu, R. C. F. F.; Souza, M. C. M. R. de; Maia, C. E. Níveis críticos para atributos do solo pela distribuição normal reduzida em culturas anais de subsistência. Revista Brasileira de Engenharia Agrícola e Ambiental , v.18, p.425-430, 2014. https://doi.org/10.1590/S1415-43662014000400010
https://doi.org/10.1590/S1415-4366201400... ) in the Sertão dos Inhamuns region of Ceará State, Brazil. Only the OM concentration was considered adequate, as indicated by those authors. These authors obtained for areas cultivated with maize and cowpea in the semiarid region the values: OM (g kg^-1): 7.3 and 7.5; pH: 6.6 and 6.5; P (mg dm^-3): 8.6 and 8.2; K (mmol_c dm^-3): 2.8 and 2.7; Ca (mmol_c dm^-3): 33.3 and 22.4; Mg (mmol_c dm^-3): 11.2 and 9.9; and base saturation (%): 73 and 71, respectively (Souza et al., 2014).

The results reported in Table 3, obtained during the two years, show increases in pH and zinc concentration in the surface layer. The higher pH can be associated with the increased organic matter content in the second year since, among other attributes, OM can absorb H⁺ (Lourenzi et al., 2011Lourenzi, C. R.; Ceretta, C. A.; Silva, L. S. da; Trentin, G.; Girotto, E.; Lorensini, F.; Tiecher, T. L.; Brunetto, G. Soil chemical properties related to acidity under successive pig slurry application. Revista Brasileira de Ciência do Solo , v.35, p.1827-1836, 2011.https://doi.org/10.1590/S0100-06832011000500037
https://doi.org/10.1590/S0100-0683201100... ).

The reduction of aluminum due to the application of organic fertilizers and the consequent increase of base saturation can be attributed to the complexing effect of organic matter, which keeps the Al concentrations low (Naramabuye & Haynes, 2006Naramabuye, F. X.; Haynes, R. J. Short-term of three animal manures on soil pH and Al solubility. Australian Journal of Soil Research, v.44, p.515-521, 2006. https://doi.org/10.1071/SR05062
https://doi.org/10.1071/SR05062... ).

There are no reports in the literature of soils in Brazil’s Northeastern semiarid region with high availability of Zn. However, it is logical to expect that increasing pH reduces these micronutrient concentrations (Nachtigall et al., 2009Nachtigall, G. R.; Nogueirol, R. C.; Alleoni, L. R. F. Extração seqüencial de Mn e Zn em solos em função do pH e adição de cama-de-frango. Revista Brasileira de Engenharia Agrícola e Ambiental, v.13, p.240-249, 2009. https://doi.org/10.1590/S1415-43662009000300004
https://doi.org/10.1590/S1415-4366200900... ).

Results of studies of fertilization using wastes from hog breeding indicate that there is an increase in pH and zinc in the soil. Still, the diets typically given to these animals contain high levels of this micronutrient, explaining increases in the soil by applying these waste materials (Ernani et al., 2001Ernani, P. R.; Bittencourt, F.; Valmorbida, J.; Cristani, J. Influência de adições sucessivas de zinco, na forma de esterco suíno ou de óxido no rendimento de matéria seca de milho. Revista Brasileira de Ciência do Solo , v.25, p.905-911, 2001. https://doi.org/10.1590/S0100-06832001000400013
https://doi.org/10.1590/S0100-0683200100... ). In the present study, the sheep manure employed came from animals of Triunfo Farm, in an extensive grazing system (with native Caatinga pasture), without feed supplementation.

Applications of organic compost made from wastes from small ruminants (goat and sheep slaughterhouse wastes and manure) were able to increase the concentration of zinc in the soil, rising with increased doses (Souza et al., 2016Souza, H. A. de; Melo, M. D.; Primo, A. A.; Vieira, L. V.; Pompeu, R. C. F. F.; Guedes, F. L.; Natale, W. Use of organic compost containing waste from small ruminants in corn production. Revista Brasileira de Ciência do Solo , v.40, p.1-16, 2016. https://doi.org/10.1590/18069657rbcs20150385
https://doi.org/10.1590/18069657rbcs2015... ), indicating that even the dung from sheep with diets not rich in zinc can be a source of this nutrient. Nachtigall et al. (2009Nachtigall, G. R.; Nogueirol, R. C.; Alleoni, L. R. F. Extração seqüencial de Mn e Zn em solos em função do pH e adição de cama-de-frango. Revista Brasileira de Engenharia Agrícola e Ambiental, v.13, p.240-249, 2009. https://doi.org/10.1590/S1415-43662009000300004
https://doi.org/10.1590/S1415-4366200900... ) evaluated the concentrations of zinc fractions due to the addition of poultry litter in the soil, concluding that despite the increase in OM, the added material had low complexation, so it did not contribute to increasing adsorption of this element.

The results for the variables P, K, Ca, and Mg concentrations in the soil have also been reported in other studies of the use of organic fertilization (Oliveira et al., 2014Oliveira, L. B. de; Accioly, A. M. A.; Santos, C. L. R. dos; Flores, R. A.; Barbosa, F. S. Características químicas do solo e produção de biomassa de alface adubada com compostos orgânicos. Revista Brasileira de Engenharia Agrícola e Ambiental , v.18, p.157-164, 2014. https://doi.org/10.1590/S1415-43662014000200005
https://doi.org/10.1590/S1415-4366201400... ; Silva et al., 2015Silva, A. A.; Lana, A. M. Q.; Lana, R. M. Q.; Costa, A. M. da. Fertilização com dejetos suínos: Influência nas características bromatológicas da Brachiaria decumbens e alterações no solo. Engenharia Agrícola, v.35, p.254-265, 2015. https://doi.org/10.1590/1809-4430-Eng.Agric.v35n2p254-265/2015
https://doi.org/10.1590/1809-4430-Eng.Ag... ; Souza et al., 2016Souza, H. A. de; Melo, M. D.; Primo, A. A.; Vieira, L. V.; Pompeu, R. C. F. F.; Guedes, F. L.; Natale, W. Use of organic compost containing waste from small ruminants in corn production. Revista Brasileira de Ciência do Solo , v.40, p.1-16, 2016. https://doi.org/10.1590/18069657rbcs20150385
https://doi.org/10.1590/18069657rbcs2015... ).

The reduction of the potential acidity can be explained by analogous reasoning to that involving pH. The increase of the CEC can be attributed to the rise of organic matter from the sheep manure. Similar results were observed by Oliveira et al. (2014Oliveira, L. B. de; Accioly, A. M. A.; Santos, C. L. R. dos; Flores, R. A.; Barbosa, F. S. Características químicas do solo e produção de biomassa de alface adubada com compostos orgânicos. Revista Brasileira de Engenharia Agrícola e Ambiental , v.18, p.157-164, 2014. https://doi.org/10.1590/S1415-43662014000200005
https://doi.org/10.1590/S1415-4366201400... ).

Concerning sulfur, Abreu Júnior et al. (2002Abreu Júnior, C. H.; Muraoka, T.; Oliveira, F. C. Carbono, nitrogênio, fósforo e enxofre em solo tratado com composto de lixo urbano. Revista Brasileira de Ciência do Solo, v.26, p.769-780, 2002. https://doi.org/10.1590/S0100-06832002000300022
https://doi.org/10.1590/S0100-0683200200... ) evaluated organic composts and observed higher S concentrations, mainly due to mineralization of organic matter, similar to our findings.

The organic matter concentration fitted to a quadratic model, being the possible explanation a priming effect, that is a stimulus to microbial activity by the additional source of organic matter (like sheep manure), and this stimulus increases the decomposition rate of the native organic matter (Kuzyakov et al., 2000Kuzyakov, Y.; Friedel, J. K.; Stahr, K. Review of mechanisms and quantification of priming effects. Soil Biology & Biochemistry, v.32, p.1485-1498, 2000. https://doi.org/10.1016/S0038-0717(00)00084-5
https://doi.org/10.1016/S0038-0717(00)00... ); thus, the priming effect and the organic matter protection depends on soil and native organic matter properties, including aspects related to texture and mineralogy (Pereira et al., 2018Pereira, M. S.; Blum, J.; Souza, H. A. de; Taniguchi, C. K. Organic carbon decomposition in soil amended with organic compost from slaughterhoue residues. Journal of Agricultural Science, v.10, p.7-14, 2018. https://doi.org/10.5539/jas.v10n8p7
https://doi.org/10.5539/jas.v10n8p7... ). On the other side, the soil texture is sandy (Table 1), corroborating this justified.

At the field conditions, the manure decomposition rate is strongly influenced by rain in the experimental period (Souto et al., 2005Souto, P. C.; Souto, J. S.; Santos, R. V.; Araújo, G. T.; Souto, L. S. Decomposição de estercos dispostos em diferentes profundidades em área degradada no semi-árido da Paraíba. Revista Brasileira de Ciência do Solo , v.29, p.125-130, 2005. https://doi.org/10.1590/S0100-06832005000100014
https://doi.org/10.1590/S0100-0683200500... ). About the priming effect, there are experiments in laboratory conditions that mention high doses of organic composts proportion to this stimulus of microbial activity (Pereira et al., 2018Pereira, M. S.; Blum, J.; Souza, H. A. de; Taniguchi, C. K. Organic carbon decomposition in soil amended with organic compost from slaughterhoue residues. Journal of Agricultural Science, v.10, p.7-14, 2018. https://doi.org/10.5539/jas.v10n8p7
https://doi.org/10.5539/jas.v10n8p7... ). The authors said that high doses would surpass the protection capacity of the soil, sharing the added organic material into two pools: protected and unprotected against microbial decomposition; thus, the greater the amount applied, the greater will be the share of the unprotected pool (Pereira et al., 2018). So, a higher decomposition rate at higher doses would be expected (Pereira et al., 2018).

With a dose of 25 Mg ha^-1 in lettuce, Figueiredo et al. (2012Figueiredo, C. C. de; Ramos, M. L. G.; McManus, C. C.; Menezes, A. M. de. Mineralização de esterco de ovinos e sua influência na produção de alface. Horticultura Brasileira, v.30, p.175-179, 2012. https://doi.org/10.1590/S0102-05362012000100029
https://doi.org/10.1590/S0102-0536201200... ) mention that sheep manure increases soil microbial activity.

The results obtained for P in the second evaluation (2016) in the subsurface layer corroborate those of Souza et al. (2016Souza, H. A. de; Melo, M. D.; Primo, A. A.; Vieira, L. V.; Pompeu, R. C. F. F.; Guedes, F. L.; Natale, W. Use of organic compost containing waste from small ruminants in corn production. Revista Brasileira de Ciência do Solo , v.40, p.1-16, 2016. https://doi.org/10.1590/18069657rbcs20150385
https://doi.org/10.1590/18069657rbcs2015... ), who noted increases in the concentration of this nutrient due to the surface application of organic fertilizers.

When planting the ‘sabiá’ seedlings, the manure was mixed with the soil used to refill the pit, with a depth of 0.4 m. The second application was as topdressing on the surface under the projection of the canopy. According to Novais et al. (2007Novais, R. F.; Smyth, T. J.; Nunes, F. N. Fósforo. In: Novais, R. F.; Alvarez V., V. H.; Barros, N. F.; Fontes, R. L. F.; Cantarutti, R. B.; Neves, J. C. L. (eds.) Fertilidade do solo. Viçosa: Sociedade Brasileira de Ciência do Solo, 2007. p.276-374.), the addition of organic materials reduces the soil’s capacity to adsorb P, increasing its availability. Further, according to those authors, the organic matter blocks the adsorption sites of the Fe and Al oxides present in the soil, diminishing the phosphorus fixation capacity.

Another explanation for the increase of P in the subsurface layer is the slow release of this nutrient by mineralization from the manure applied in the pit (García-Orenes et al., 2016García-Orenes, F.; Roldán, A.; Morugán-Coronado, A.; Linares, C.; Cerdà, A.; Caravaca, F. Organic fertilization in traditional Mediterranean grapevine orhards mediates changes in soil microbial community structure and enhances soil fertility. Land Degradation & Development, v.27, p.1622-1628, 2016. https://doi.org/10.1002/ldr.2496
https://doi.org/10.1002/ldr.2496... ). For the increase of Fe in the subsurface layer, a possible explanation is related to the high concentration in the manure (3.9 g kg^-1).

In an experiment that studied the nutrient release during decomposition of different manures in the semiarid region of Paraíba State, Brazil, the sheep manure had the highest levels of N, P, Ca, and Mg (Souto et al., 2013Souto, P. C.; Souto, J. S.; Nascimento, J. A. M. do. Liberação de nutrientes de estercos em Luvissolo no Semiárido paraibano. Revista Caatinga, v.26, p.69-78, 2013.), which contributed with the results that showed increase in the attributes of soil fertility (Tables 3 and 4).

Even though ‘sabiá’ is a leguminous species, with the capacity for biological nitrogen fixation (BNF), according to García-Orenes et al. (2016García-Orenes, F.; Roldán, A.; Morugán-Coronado, A.; Linares, C.; Cerdà, A.; Caravaca, F. Organic fertilization in traditional Mediterranean grapevine orhards mediates changes in soil microbial community structure and enhances soil fertility. Land Degradation & Development, v.27, p.1622-1628, 2016. https://doi.org/10.1002/ldr.2496
https://doi.org/10.1002/ldr.2496... ), the sheep manure application increases the nitrogen present in the soil and plants.

It was not verified increases of B in the soil with rising doses of sheep manure. Still, there was higher content of this micronutrient in the plants, so organic fertilizers can be an excellent source to supply this nutrient, as reported by Dey et al. (2015Dey, A.; Dwivedi, B. S.; Datta, S. P.; Meena, M. C.; Agarwal, B. K. Soil boron status: Impact of lime and fertilizers in an Indian long-term field experiment on a Typic Paleustalf. Acta Agriculturae Scandinavica, v.65, p.54-62, 2015. https://doi.org/10.1080/09064710.2014.966142
https://doi.org/10.1080/09064710.2014.96... ).

Another impressive result was the content increase of all macronutrients and B in the plant with the rise of sheep manure doses (Table 2), which reinforce the results obtained in the soil.

Conclusions

Acknowledgments

The authors wish to thank the ‘Projeto Biomas’, Empresa Brasileira de Pesquisa Agropecuária (Embrapa), Confederação da Agricultura e Pecuária do Brasil (CNA) and Banco Nacional de Desenvolvimento Econômico e Social (BNDES) for supporting this research.

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