Phosphorus cycling byUrochloa decumbensintercropped with coffee

Abstract

Summary Phosphorus (P) is a limiting resource for agricultural production in the tropics. Urochloa spp. is commonly used as a cover crop and has mechanisms to mobilize partially the nonavailable P forms from the soil. The use of Urochloa intercropped with Arabica coffee (Coffea arabica L.) is increasing in Brazil, but P cycling has been overlooked in this system. Here, we proposed two experiments to test the hypothesis that Urochloa decumbens could mobilize and absorb P from deep soil layers and increase overall P cycling of the intercrop system. We measured U. decumbens root and shoot dry mass (SDM), root morphology and activity, nutrient uptake, soil nutrient availability, and soil P fractionation in both experiments. To better understand P cycling by Urochloa alone, in the first experiment, U. decumbens was cultivated in rhizotrons where adequate P was supplied in distinct soil layers – 0.0 to 0.3 m, 0.3 to 0.8 m, 0.8 to 1.3 m, and 1.3 to 2 m. Root dry mass (RDM) and morphology were not affected by P availability. Moreover, total biomass production (root plus shoot) and P uptake were higher when P was available in the superficial top soil layer compared to P availability in more than one layer or only in the bottom layer. Nevertheless, U. decumbens was able to reach and acquire P from depth. Correlation analysis showed that P cycling was strongly dependent on SDM, labile, and moderately labile fractions of soil P and was not significantly correlated with RDM. The second experiment aimed at verifying P uptake and mobilization from different soil depths in field conditions. P was supplied in different depths of the soil profile – 0.3 m, 0.6 m, and 0.9 m – in the field with preestablished U. decumbens intercropped with Arabica coffee plants. Shoot P content was higher at the first sample date when P was supplied at 0.3 m, compared to 0.6 m, 0.9 m, and control with no P. Soil P fractionation showed that there was no P mobilization of less labile forms by U. decumbens during the evaluated time. Our results showed that P fertilization in the top layer rather than suppling P trough the soil profile can maximize U. decumbens growth. Also, Urochloa P accumulation was enough to support coffee demand even in high yields and can be an alternative to increase P use efficiency in coffee production systems, being an effective recycler of P.

Arbuscular Mycorrhizae for Sustainable Cultivation of Grasses

“…Different AMF species (Acaulospora longula and Acaulospora colombiana) were previously reported by Barbosa et al [8] as associated to U. brizantha in greenhouse, also in Minas Gerais, Brazil Table 1 shows limited available reports on Urochloa species and their associated microbiomes in Brazil. In the present study, the AMF community structure was studied in a grassland in Brazil, The AMF community structure in the U. brizantha experimental plot showed dominance of Glomeraceae, compared to other reports (Table 1) where Acaulospora and Gigaspora were inoculated and, thus, theoretically occurred, such as in the reports by Baptistella et al [6,7]. In the present work, five genera of Glomeromycota, four species and four unidentified morphotypes were detected in the U. brizantha grassland.…”

“…Furthermore, AMF secret a protein (glomalin), which favors soil aggregation, improving soil quality. In this sense, only one report showed the soil glomalin content in U. brizantha, which, varied from 3.30 to 3.74 mg. g soil −1 when inoculated with G. margarita and A. longula, respectively [6]. The low glomalin content when inoculated with Gigaspora sp.…”

“…Urochloa roots also improve soil physical characteristics and influence soil nutrient dynamics, reducing nutrient losses and enhancing their cycling, which is benefic for nutrient use efficiency in sustainable agriculture. Furthermore, these cover crops are commonly employed in coffee trees [6] and in many orchards. Thus, meliorating the U. brizantha culture via benefits from AMF and increasing research on the symbionts and related microbiota, will favor sustainable grassy ecosystems destinated to forage, which can also provide sustainable plant systems to reproduce AMF propagules.…”

“…Thus, Urochloa decumbens is also used for arbuscular mycorrhizae multiplication, in addition to its cultivation for ensuring the sustainability of livestock systems. Moreover, these grass species is increasingly used in no-tillage ecosystems as cover crops [5], such as in coffee trees [6]. Some grass species actively propagate benefic microsymbionts after their roots are colonized by the soil microbiota.…”

Agronomic practices toward coffee sustainability. A review

“…This characteristic is exciting since coffee is also quite colonized and depends on mycorrhizas to acquire nutrients, mainly P, and contributes to the positive water status of coffee plants (Andrade et al, 2009(Andrade et al, , 2010. Moreover, several authors have shown that the roots of Urochloa were active and capable of absorbing nutrients even at a depth of 1m in the interrow of coffee and that they were capable of mobilizing part of the non-readily available P, recycling enough P to satisfy the demand for high coffee yields (Baptistella et al, 2022).…”