T. K. Srivastava

Plant Growth-Promoting Bacteria: An Emerging Tool for Sustainable Crop Production Under Salt Stress

Salinization, recognized as one of the most devastating soil degradation threats on earth, has endangered the potential use of soil on almost an estimated land area of about 1 billion ha globally, representing about 7 % of earths continental extent of which about 20 % is cultivated land area. It is not only suppressing plant growth but is also disturbing the sustainability of beneficial microorganisms associated with the plant rhizosphere. The agricultural crops under salinity are known to exhibit a spectrum of responses ranging from crop yield declines to disturbance in ecological balance of the region. It is a major cause of land abandonment and aquifers for agricultural purposes. The impacts include poor agricultural productivity, low economic returns and soil erosions. PGPRs, which live in association with plant roots that alleviate salt stress for better growth and yield, through their own mechanisms for osmotolerance, osmolyte accumulation, asymbiotic N2 fixation, solubilization of mineral phosphate and other essential nutrients, enhanced NPK uptakes, production of plant hormones, ACC production, scavenging ROS, ISR and IST, are an important alternative to traditional agricultural techniques. The present chapter focuses on the advantages of PGPR-based mechanics through an engineered increase in tolerance to salinity and conceptual understanding of crop productivity as a complex product of plant genetics and microbial community function. The direct and indirect mechanics of PGPR through bio-fertilization, stimulation of root growth, rhizo-remediation and plant antibiosis and induction of systemic resistance, nutrient competition and niches that assists to sustain healthy growth of plants enhancing the crop productivity are also accentuated.

Bio-organic Amendment of Udic Ustochrept Soil for Minimizing Yield Decline in Sugarcane Ratoon Crops under Subtropical Conditions

The effects of subsequent sugarcane ratooning on soil quality and the crop yields under four treatments [an absolute control (T0), application of recommended dose of nitrogen (N)–phosphorus (P)–potassium (K) (T1), application of sulfitation press mud (SPM), a sugar factory by-product (T2), and SPM along with Gluconacetobacter diazotrophicus (Gd, T3)] were evaluated for 7 years. In the control (T0) and NPK-fertilized (T1) plots, an increase in soil compaction (5.4%), decrease in infiltration rate (6.04%), lower microbial activities, and increased soil phenolic contents (72.4%) rendered the nutrients unavailable, leading to significant declines in the crop yields at the rate of 5.47 Mg ha−1 y−1 and 4.67 Mg ha−1 y−1, respectively. The crop yield declined from 53 kg ha−1 in plant crop to 18 kg ha−1 in the sixth ratoon crop under the absolute control. The rates of yield decline, however, were minimized in SPM (T2) and SPM + Gd (T3) plots to 3.54 and 3.51 Mg ha−1 y−1.

Soil-Root Interface Changes in Sugarcane Plant and Ratoon Crops under Subtropical Conditions: Implications for Dry-Matter Accumulation

Poor sugarcane ratoon yields in the subtropics are responsible for decrease in overall productivity and poor sugar recovery. The present work is an attempt to assess reasons for decline in crop productivity despite providing adequate inputs. The simultaneously initiated plant and ratoon crops were compared for dry-matter accumulation and its distribution pattern in relation to changes in soil-root interface environment. In spite of well-established root system and advanced sprouting and tillering during the formative phase, dry-matter accumulation and nutrient uptake were low in a ratoon crop and were more apparent 120–210 days after planting. This decrease in nutrient uptake was due to declines in soil cation-exchange capacity, nitrate reductase (NR) activity in vivo by 19.4 and 25.9 percent, and increase in percentage leakage by 11.26 percent. These alterations at the soil-root interface in ratoons functioned as barriers for nutrient uptake and affected overall physiological growth and dry-matter accumulation adversely.