Influence of phosphorus on initial growth and production of fresh biomass of legumes . ABSTRACT Aims: To evaluate whether the initial growth and production of green biomass of the legume species Crotalaria juncea L. and Canavalia ensiformis (L.) DC. are influenced by phosphate fertilizer. Study design: A completely randomized design was used in a scheme 05 treatments x 02 cultures, with 3 replications, totaling 30 vessels in the experiment. Place and Duration of Study: Forest nursery the Federal University of Campina Grande, campus of Patos-PB, between April 2018 and May 2018. Methodology: The treatments consisted of two legumes (C. juncea and C. ensiformis) and -1 five doses of phosphorus (00-50-100-150-200 mg kg of P2O5) through Simple Superphosphate. Fortnightly measurements of height and diameter were performed for 60 days. Fresh biomass of the shot and root was obtained at the end of the evaluations. Results: There is a higher growth in height for individuals of C. ensiformis when cultivated in doses of 150 mg kg-1, with an average of 30.68 cm. For C. juncea, the treatments were similar. For the stem diameter, there was significant interaction (p <0.05) only for C. juncea, in which, unlike the results obtained for height, this variable grew linearly with increased phosphorus doses. Regardeless of the P doses fresh biomass production of C. ensiformis was higher than to C. juncea. When analysing the unfolding unfolding of P at each legume level, there is an influence of nutrient levels only for C. ensiformis, with higher total biomass -1 production and when cultivated with 100 mg kg of P2O5. Conclusion: Regardless of the cultivated species phosphorus influences the initial growth and production of fresh biomass. In general, it is recommended to cultivate the legumes -1 studied with doses of 100 mg kg of P2O5 through simple super phosphate for a higher production of total fresh biomass. Keywords: Irrigated Perimeters; Recovery of Degraded Areas; Sustainability; Green Manure; Crotalaria juncea; Canavalia ensiformis. 1. INTRODUCTION The implementation and development of irrigated agriculture in the country is a common and growing practice, but when performed inadequately it promotes several environmental impacts, especially those related to the salinity and sodicity soil [1, 2]. Most of these problems occur in arid and semi-arid regions, because in addition to most agricultural activities being irrigated, annual rainfall does not ensure the washing of mineral salts accumulated in the soil [3, 4]. According to Lima Jr and Silva [5] in the semi-arid region of northeastern Brazil, the highest incidences of areas with salinization are concentrated in the most intensively cultivated lands with the use of irrigation, in the so-called Irrigated Perimeters. Over the years, these areas tend to be abandoned due to reduced soil fertility and agricultural productivity. It is important to study techniques that improve the chemical, physical and biological properties of the soil, and consequently raise the productivity of the species cultivated there. Siqueira et al [6] also comment on the need for intervention through conservation practices and Nogueira et al [7] mention green manure as one of the most prominent practices. Green manure is a vegetative practice that consists of incorporating of non-decomposed plant material into the soil. It is considered a sustainable option for the reestablishment of soil conditions, because in addition to improving the properties of the soil, it provides nutrients to plants, assists in water retention and also reduces the use of chemical fertilizers [8, 9, 10]. Legumes are the most used groups of plants used when working with green manure. According to Massadah et al [11] these species provide several benefits to the soil, such as for the cultivated species, in general they are able to perform the biological fixation of N2 through nitrogen-fixing bacteria associated with its root system. Among the numerous species that can be used as green fertilizer, Crotalaria juncea L. and Canavalia ensiformis (L.) DC. has been standing out. According to Araújo [12] C. juncea is an exotic species of Asian origin, of annual cycle, shrubby legume and belonging to the family Fabaceae, Faboideae (Papilionoideae). Garcia et al [13] comment that the species stands out for its rapid growth and easy adaptation to adverse conditions, besides its great nitrogen-fixing potential. C. ensiformis is a legume used under various edaphoclimatic conditions, being adapted to regions of arid and semi-arid, or even tropical. With great potential for biomass and nitrogen supply, this species is still widely used in consortia with other crops. Gebauer [14] also comments that the species also has properties used in the control of phytopathogens present in the soil. Raij [15] explains that phosphorus (P) is one of the macronutrients with low natural availability in most soils from throughout the Brazilian territory, being the nutrient, most used in the fertilization process. In addition to participating in several compounds in the vegetables fundamental to various metabolic processes, in its absence, the plant becomes unable to complete its life cycle. [15]. Considering these characteristics, it is important to analyze these species, as well as their relationship with nutritional sources, in order to provide information about their potential use to reintegrate degraded soils from Irrigated Perimeters to the farm. Based on the above, the study aims to evaluate whether the initial growth and production of green biomass of the legume species C. ensiformis and C. juncea are influenced by phosphate fertilizer. 2. MATERIAL AND METHODS The experiment was conducted in the forest nursery of the Center for Health and Rural Technology (CSTR) of the Federal University of Campina Grande (UFCG), Patos-PB campus, in an environment with solar reduction factor and protection against rain. According to the classification of Köppen [16] the climate is of type BSh, considered semi-arid hot and dry. The soil was collected in the irrigated perimeter known as Engenho Arco verde, located in the municipality of Condado-PB. To characterize the physicalchemical attributes of the soil (presented in Tables 1 and 2) samples were collected at a depth of 0-20 cm, sent to the Soil and Water Laboratory (LASAG) of CSTR/UFCG and analyzed according to the methodologies proposed by Raij et al [17] and Amaro Filho, Assis Jr and Mota [18]. Table 1. Chemical attributes of the soil collected in the irrigated perimeter Engenho Arco Verde located in Condado-PB. pH P Ca Mg K Na H+Al CTC V mg kg-1 ------------------------------- cmolc dm-3 ----------------------------- % 6.50 25.40 6.00 3.60 0.38 0.26 1.20 11.44 89.51 *Hydrogenionic Potential (pH), Phosphorus (P), Calcium (Ca), Magnesium (Mg), Potassium (K), Sodium (Na), Total Acidity (H + Al), Cation Exchange Capacity (CTC pH 7.0) and Base Saturation (V%) Table 2. Physical attributes of the soil collected in the irrigated perimeter Engenho Arco Verde located in Condado-PB. Granulometry Textural class -------------------------g kg-1------------------------ SBCS SAND SILT CLAY 765 137 98 Light sandy *SBCS - Brazilian Society of Soil Science The seeds of C. juncea (Crotalária) and C. ensiformis (Feijão-de-porco) were provided by the Agroecology course of the Semiarid Development Center (CDSA) of UFCG, Sumé-PB campus, followed by their selection, removing the damaged ones and with injuries. No-tillage was performed, placing five seeds per pot, and after eight days thinning was done, leaving the two plants with greater vigor. The soil was maintained at 70% of the field capacity. The treatments were composed of two legumes (C. juncea and C. ensiformis) and five doses -1 of phosphorus (00-50-100-150-200 mg kg of P2O5) via Simple Superphosphate (SS). The SS was previously ground and homogenized with the soil. Thus, the IHD (completely randomized design) was used in a scheme 05 treatments x 02 cultures, with 3 replications, totaling 30 vessels in the experiment. Fortnightly measurements of height and diameter were performed using a ruler graduated in centimeters (cm) and a digital caliper in millimeters (mm) respectively for 60 days. At the end of the evaluations, fresh biomass was obtained from both shoots and root. For this procedure, steel stiletto was used to separate the shoot from the root and trays to separate the soil from the roots. Subsequently, the material was weighed with the aid of the precision electronic scale. After tabulating the data, statistical analysis was performed using the SISVAR 5.7 software [19]. For the comparative effect of green manure, the Tukey test was applied at 5% and for the dose effect, grade 2 polynomial regression was applied. 3. RESULTS AND DISCUSSION There is a higher growth in height for individuals of C. ensiformis cultivated at doses of 150 mg kg-1, with an average of 30.68 cm. When comparing this result with the treatment without the addition of P2O5 (control), a difference of 6.53 cm is observed, indicating that phosphorous is fundamental for the initial growth of this species. There is also a reduction in plant height at doses higher than 150 mg kg-1 (Figure 1), demonstrating the importance of applying correct amounts of nutrients in the soil, because excessive levels in besides causing problems in plant development, can harm the environment and bring unnecessary economic damage. Coutinho et al [20] also verified a negative effect of the excess availability of P to the Vigna unguiculata (L.) Walp crop. For C. juncea, the treatments were similar, in which there was a difference of smaller than 3 cm from the dose with the highest mean in relation to the lower. It is also possible to observe a decreasing linear behavior, indicating that the height of the plants decreased with the addition of phosphorus (Figure 1).