Resposta da soja e do repolho à concentração de nutrientes e volume do meio radicular

Abstract

In soil preparation methods either by no till or by raised beds for vegetable crop production, root growth can be reduced by subsurface compaction and concentration of fertilizers in the surface layer. The goal of this research was to test the concentration of nutrients may offset situations of physical restriction to root growth without reducing shoot growth and production of soybean and cabbage. Two experiments were carried out at IFFarroupilha – São Vicente do Sul, RS, from December 19, 2012 from May 17, 2013 and from December 12, 2015 to March 13, 2015, respectively. In the first experiment “U” shape wooden gullies were made up with two similar compartments inside them for root growth. Water and nutrients were separately supplied to plants in each one of compartments by subirrigation. Nutrients were supplied by means of a complete nutrient solution (NS) in concentrations of zero (0-only water), 50% (50) and 100% (100) of it, in five combinations in the two compartments. In T1, 50% concentration was supplied in both gully compartments (50/50). In T2, it was 50% in one and 100% in the other compartment (50/100); in T3, zero (water) and 100 % (0/100); in T4, zero (water) and 50% (0/50) and in T5 it was 100% in both compartments (100/100). In the second experiment, soybean plants were grown in 0.4 dm3 (V1) and 3.0 dm3 (V2) pots and daily fertigated with the previous NS at its normal concentration (C2) and diluted to 20% (C1). Data of the first experiment showed that growth of soybean plants at R1 was 30% higher on plants supplied with 100/100 and 50/100 NS concentrations while at R6 it was lowest in the 0/50. Lower root growth was recorded where nutrients were supplied in only one side of gullies. Growth of cabbage plants at 62 DAP was higher on plants supplied with 0/100 and maximum root growth was recorded on gullies with nutrients supplied in both sides (50/50 and 100/100). In the second experiment, interactions were found among NS concentrations and pot volumes on plant growth, except for grain production, which did not show differences among treatments. Higher pod abortion was recorded on plants supplied with the C2 concentration, in both pot volumes. Higher number of grains was recorded on C2V2 plants, but the size of grains was lower. It was concluded that root growth of soybean and cabbage plants is directed toward the higher concentration of nutrients in the root medium and when supplied quantities of nutrients are enough to attain those extracted by plants, maximum growth might be expected, irrespective of the position of nutrients in the root medium. Root confinement of soybean plants regularly supplied with water and nutrients reduces plant growth but did not affect significantly grain production. The high nutrient concentration partially compensates the reduction on root growth by effect of confinement.