Effect of Soil Salinity on Growth and Yield of Sugar Beet (Beta Vulgaris L)

Abstract

Salinity is a serious threat to agriculture in arid and semi-arid regions of the world. The situation is also critical and alarming in the Sindh Province of Pakistan, where more than 35% of the irrigated area is salt-affected. The purpose of this research was to study the effect of soil salinity on growth, beet yield and juice quality of sugar beet (Beta vulgaris L.). Sugar beet is salt-tolerant, short duration and low delta crop as compared to other sugar crops including sugarcane. A series of four experiments was conducted by involving ten sugar beet genotypes, viz. California, Ernestina, Magnolia, Mirabella, Sandrina, SD-12970, SDPAK 03/06, SDPAK 01/07, SDPAK 07/07 and SD PAK 09/07. These genotypes were tested against a wide range of salinity. In first study, sugar beet plants were stressed with five salinity levels (control, 4, 8, 12, and 16 dS m-1). The effect of EC 4 and 8 (dS m-1) was found to be encouraging on almost all the measured growth, yield and juice quality traits. Thereafter, EC 8 (dS m-1) salinity showed declining effect on these parameters. Increasing salinity consistently increased the accumulation of osmo-protectant (proline), Na+ and Cl- ions in leaves. In contrast increasing salinity showed decreasing trend for K+ and K+/ Na+ ratio. The sugar beet genotypes California, SDPAK 09/07, SDPAK 03/06, SDPAK 01/07 showed better performance by acquiring less Na+, more K+, high K+/Na+ ratio and considerable amount of leaf proline under salt-stress environment. In second study the same ten genotypes were tested against similar salinity levels on silty clay loam and clay soils. Irrespective of soil texture as against control, like I in study 2, the salinity of EC 4 and 8 (dS m-1) did not show negative effect on growth, beet yield and juice quality. Generally, the difference between two soil textures was significant for these traits at almost all salinity levels. Compared to silty clay loam soil, the negative effect of salinity on sugar beet plants in clay soil was associated with higher Na+ and lower leaf K+/Na+ ratio. These genotypes were ranked on the basis of salt-tolerance traits index (STTI). In clayey soil, the ranking of sugar beet genotypes was: Ernestina > Magnolia > SD PAK 09/07 >Mirabella > California > Sandrina > SDPAK 03/06 > SD PAK 01/07 > SDPAK 07/07 > SD-12970 at EC 12 and 16 dS m-1. In silty clay loam soil, the ranking was SDPAK 03/06 > California > SDPAK 09/07 > SDPAK 01/07 > Mirabella > Ernestina > Sandrina > Magnolia > SD-12970 > SDPAK 07/07 at same salinity levels. The next set of pot and field trials (Study 3 and 4) was conducted involving a saline soil (EC 9 dS m-1) to determine the effect of two different planting techniques (direct and transplanting) on sugar beet growth, yield, quality and ions content. Transplanted beet plants performed better over directly planted dry seed under both pot and field studies in terms of some growth, development (number of leaves, fresh and dry leaf weight), ion content (Na+ K+, Cl- and K+/Na+ ratio) and juice quality traits (brix %, pol % and sugar recovery %).Transplantation under field condition did not show improvement in beet and sugar yields as it showed in pot conditions. The genotypes SDPAK 09/07, SDPAK 01/07, California, SDPAK 03/06 and SD-12970 performed better in both pot and field experiments. These studies concluded that salinity of EC 4 and 8 (dS m-1) did not reduce growth, beet yield and juice quality of sugar beet. In general, genotypes California, SDPAK 09/07, SDPAK 03/06, SDPAK 01/07 performed better in all four studies by displaying less Na+, more K+, higher K+/Na+ ratio and synthesis of considerable amount of proline in overall salinity levels as against their counterparts. Silty clay loam soil was superior over clay soil for obtaining more beet yield and better quality juice.