Propriedades físico-hídricas de solo e rendimento de sorgo em cultivo de vazante

Abstract

In Northeast Brazil, more than 70.000 small dams retain superficial run off and underground water flow, creating small reservoirs. Flood recession agriculture consists of cropping the margins of the reservoirs, on slight slopes, while the water level progressively decreases, and it is a widespread cropping system in this region. It is characterized as a means of survival and self-sustenance that comes from the beginnings of agriculture, and that persists to this day, especially in semiarid. Few studies have been conducted on flood recession agriculture, particularly with regard characterization of hydraulic parameters and models that describe this specific condition of unsaturated soils. This proposed research aims to evaluate the physical-hydric characteristics of soil on flood recession agriculture cropped with sorghum and subjected to two ground cover conditions: with and without mulch. This study also sought to examine the behavior of four sorghum varieties (IPA 2502, IPA4202, IPA and IPASF 25467-4-2) submit them to the conditions of absence and presence of mulch. The sorghum crop was chosen for its ability to survive and produce under conditions of limited waters up plies over long periods of dry conditions usually found at the end of the flood recession agriculture. Cattail (Typha domingensis), plant of the flooded regions, typical of wetlands and floodplains, also found in semiarid, but is essentially cosmopolitan, was chosen as mulch depending on the availability of abundant biomass and by not being a food source human and / or animal of the region. The effects of flood recession agriculture on the physical - hydric properties of the soil, conserving water in the soil and consequently yield of sorghum were evaluated in 2012 at the Experimental Station of the Agronomic Institute of Pernambuco - IPA, region of Pajeú, semiarid of the Pernambuco. It was essential to the study and understanding of water dynamics in soils for proper management and obtaining better yields of crop cultivation ebb. Sorghum was cultivated with spacing of 0.8 m between rows and 0.15 m between plants. The design was a randomized block design with four replications arranged in a factorial design (4x2). The physical-hydric properties were evaluated water hydraulic conductivity, bulk density, resistance to penetration, porosity and water content in the soil. To determine the hydraulic conductivity was used infiltrometer with controlled suction disc 8 cm in diameter and the measurements soils penetration resistance (RP) was used impact penetrometer Model (IAA-Planalsucar). The measurements were performed between plants in the central rows of cultivation. Parallel data were evaluated for plant height, flowering initial percentage of surviving plants and biomass production. For data analysis we used the statistical program Sisvar, being employed the Tukey test at 5% probability to compare the treatment means. The measures of the physical and hydraulic properties of soil have been realized on two times: at the beginning of cultivation, after treatment installation in the experimental area (1st test campaign) and between reproductive and maturity stages of grains (2st test campaign). In the first measurement campaign, the hydraulic conductivity values (K(h)) were higher in the soils without mulch for all cultivars, except in the soils cropped with sorghum varieties IPA 4202 and IPA 467-42 in the soil water pressure head h (0 and -2 cm). In the second measurement campaign, the mulch offers a decrease for hydraulic conductivity (K(h)) for all treatments, except for K(h) values in the soil water pressure head h (-12, -6 and -2 cm) of soils cropped whit sorghum variety IPA 2502. The highest yields of biomass are obtained for the cultivars IPA 467-42 and IPA SF-25. Mulching effect was significant in dry matter for the IPA SF-25variety. Mulched sorghum plants (IPA SF-25 variety) produced more dry matter than the unmulched plants. The average yield of 12.85 t DM / ha of the experiment indicates that the growing tide is an excellent alternative to sorghum production in the dry season.