Document Type : Original Article
Authors
1
Soils and Water Department, Faculty of Agriculture, Benha University, Toukh, Egypt
2
Soils, Water and Environment Research Institute (SWERI), Agricultural Research Center (ARC), Giza, Egypt
3
3Soils and Water Department, Faculty of Agriculture, New Valley University, Egypt
4
National Committee of Soil Science, Academy of Scientific Research and Technology, Egypt
5
Department of Agricultural Science, Higher Institute for Agricultural Cooperation, Qualubia, Egypt
6
Department of Soil and Water Sciences, Faculty of Agriculture, Kafrelsheikh University, Egypt
Abstract
Nitrogen is a crucial nutrient for sugar beet growth and productivity; however, excessive N-inputs could negatively impact sugar yield. Thus, optimizing N additions is a necessity to achieve a balance among yield, sugar content, and sustainability. The current study evaluates the feasibility of partial substitution of mineral N fertilizers with a nitrogen fixer, named Paenibacillus polymyxa in combination with humic substances -potassium humate (KH), humic acid (HA) and fulvic acid (FA)- to enhance sugar beet production under saline-sodic conditions. To attain this aim, a field experiment of a complete randomized block design was conducted over two consecutive winter seasons, comprising 8 treatments: (NH4)2SO4 applied at the recommended dose (T1), mineral-N+KH (T2), mineral-N+HA (T3), mineral-N+FA (T4), P. polymyxa (T5), +KH (T6), P. polymyxa +HA (T7) and P. polymyxa +FA (T8). A half dose of mineral-N was added to plots containing T5 to T8 to activate P. polymyxa . Results reveal that the addition of humic-extracts to mineral N-fertilizer and/or substituting N-fertilizer partially with an N-fixer significantly boosted the shoot and tuber yieldsof sugar beet as well as increased tuber length and diameter. The combination between bioinoculant with humic substances recorded the highest increases in plant growth and productivity, especially T6. Generally, ithe ncreases in shoot and tuber yields were significantly correlated with each of (1) proline-level in shoots, (2) soil organic matter (SOM) and (3) activity of N2ase enzyme. Regarding proline, its level increased in shoots of plants amended with either humic extracts and/or biofertilizers and this content was significantly correlated with each of soil organic matter and N2-activity. Although, treatment T5 did not receive organic extracts, yet it increased SOM. Thus, root exudates probably were the responsible of buildup of SOM. This organic component (SOM) was correlated negatively with both soil-bulk-density and soil-EC, while positively correlated with soil hydraulic conductivity. Soil bulk density, in turn, exhibited a negative correlation with soil ESP. Maybe root exudates increased in stressed plants to enhance the activity of nitrogenase-enzyme, thereby increasing the available N content and N-distribution within plant parts. Shoot N was correlated with shoot biomass; yet N maybe accumulated in tubers in relatively high concentrations without showing concurrent increases inits yield as observed in treatments T2-T4. By the end of the two seasons, the studied soil changed into a saline non-sodic one in all treatments after the second season. Thus, application of humic substances and biofertilizers could be a successful strategy to increase sugar beet productivity in saline sodic soils, while reclaiming of such soils needs longer time periods. Further experiments over longer time periods are needed to evaluate the feasibility and sustainability of these approaches in converting saline-sodic soils into non-saline, non-sodic ones.
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