The main purpose of the two consecutive experimental studies presented here was to compare the effect of salinity on nutrients in leaves of the halophytic plant species Portulaca oleracea L. and in soil. The first experiment was conducted to study the effect of salinity on plant growth, biomass accumulation, yield, root layer development, salt accumulation, and the dynamics of changes in mineral substances in plants and soil. In the second experiment, P. oleracea seeds were sown directly into salinized soil (treated immediately before plant growth) to determine the nutrient levels in leaves and soil. Three salinity treatments (saline water solution with NaCl: T1, 5 dS m−1; T2, 9.8 dS m−1; and T3, 20 dS m−1) and a control treatment (T0, 1 dS m−1) were used in the first experiment. The soil in the second experiment was used in a previous study (performed immediately before P. oleracea growth) (salinized soil: T1, 7.2 dS m−1; T2, 8.8 dS m−1; T3, 15.6 dS m−1; T0, 1.9 dS m−1). The plants were irrigated with tap water at amounts in the range of 0.25–0.50 L/pot. Analysis of the experimental results showed that P. oleracea is resistant to salinity, is able to remove ions (400–500 kg ha−1 NaCl), and can be grown in saline soil. The results indicated that P. oleracea is able to grow in high-salinity soil. This finding was confirmed by the dry matter obtained under high-salinity conditions. Salinity stress affected nutrient uptake in leaves and soil.

Effects of Salinity on the Macro- and Micronutrient Contents of a Halophytic Plant Species (Portulaca oleracea L.)

Biomagnification of potentially toxic elements in animals consuming fodder irrigated with sewage water

Sewage sludge (SS) in the soil acts as a slow-release organic fertilizer, and its nutrient supplying capability and heavy metal release occur for a prolonged period depending upon the applied doses. Field experiment not only evaluated the direct impact of SS application on rice (Oryza sativa L.) but also tracked the accumulation of lead (Pb), cadmium (Cd), chromium (Cr), and nickel (Ni) content in succeeding wheat (Triticum aestivum L.) crop and next-season rice and wheat crop. The field experiment was conducted with different levels of SS (15, 30, and 45 t ha−1) alone and in combination with 100% and 50% recommended doses of fertilizers (RDF). The findings indicated that the addition of SS (45 t ha−1) alone and in combination with inorganic fertilizers increased heavy metal accumulation in grain and straw of rice–wheat system and also led to enhanced DTPA-extractable metal content in post-harvest soil. Heavy metal concentrations in crops (except Cr content in straw) and soil stay below the phytotoxic limits in all treatments. However, total Cd in the soil exceeds the permissible limit with the sole application of SS beyond 30 t ha−1. This study admitted that one-time application of SS at the lower dose and reaping its benefits in subsequent crops can be an effective strategy of SS utilization in rice–wheat system.

Assessing heavy metal accumulation in plants and soil with sewage sludge application under rice–wheat system in an Indo-Gangetic Inceptisol

The present two-year experiment (2017-19) evaluated the impact of domestic sewage sludge (SS) on yield parameters and soil nutrient status under the pearl millet-wheat system using saline irrigation. The field study consisted of three irrigation treatments [canal water (0.35 dS/m); saline water (8 and 10 dS/m)], and five fertilizer treatments [control, SS (5 t/ha), SS (5 t/ha)+50% recommended dose of fertilizers (RDF), SS (5 t/ha)+75% RDF and 100% RDF]. The results revealed a significant reduction in the biological yield and yield attributes, and protein content of both crops with increasing salinity levels of irrigation water during both the years. However, all these parameters recorded significantly highest values under 100% RDF which was statistically at par with SS (5 t/ha) + 75% RDF treatment. The soil available sulphur (S) was significantly increased with 8 and 10 dS/m EC of saline water over canal water (0.35 dS/m) irrigation. But, SS (5 t/ha) + 75% RDF obtained 36.7 and 22.3% higher available S over control and 100% RDF, respectively. No significant effects were made in DTPA-extractable micronutrients (Fe, Mn, and Cu) with saline irrigation except Zn, which was reduced under saline environment. SS added treatments obtained higher micronutrient concentration over control. Hence, SS incorporation has proven useful in sustainable crop production and improved micronutrient availability in the soil.

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An assessment of domestic sewage sludge in pearl millet-wheat system under saline irrigation

The application of nutrient solutions to the foliage of plants is an alternative means to fertilise crops. Foliar fertilisation is used to overcome the disadvantages of soil applications. Variable plant responses to these foliar fertilisation spray solutions have often been described in the literature. However, knowledge about the penetration mechanisms, the role of a leaf-applied inorganic or organic solution, and the results obtained by its application is still limited. The complex character of the factors determining the effects of sprays hinders the development of suitable foliar fertilisation strategies, applicable under variable local conditions and for various plant types. This review describes some basic factors involved in the penetration process of foliar sprays in olive (Olea europaea L.) trees. Chemistry, leaf penetration, and plant nutrition principles will be merged with the aim of clarifying the constraints, opportunities, and future perspectives of sprays to cure olive tree nutrient deficiencies and, hence, both increase the yield and improve the fruit quality. 

Inorganic and organic foliar fertilization in oliveS

Salinity prompts heavy metals accumulation and adversely affects nutrient contents in soil and plants, thereby reducing crop yields. The assessment of domestic sewage sludge (SS) under saline conditions to boost crop productivity has become crucial. A field trial was conducted for two consecutive years (2017–2019) with three irrigation levels [canal water (0.35 dS m−1), I1; 8 dS m−1, I2; and 10 dS m−1 saline water, I3]; and five fertilization levels [control, F1; SS (5 t ha−1), F2; SS (5 t ha−1) + 50% RDF, F3; SS (5 t ha−1) + 75% RDF, F4; and RDF, F5]. The results revealed that treatment I3 (10 dS m−1) reduced the grain yield of pearl millet and wheat by an average of 31.2 and 32.6%, respectively, compared to I1 (0.35 dS m−1). However, among fertilizer treatments, F5 obtained significant highest grain and straw yields statistically at par with F4 treatment. Also, in the context of nutrients content in crops, a similar trend has been reported. In the addition, with the usage of saline irrigation (EC 8 and 10 dS m−1) and SS (5 t ha−1), the availability of heavy metals in crops and soil had increased (p = 0.05). The soluble ions in soil increased with increasing salinity levels of irrigation water. The extractability series of heavy metals were: Pb > Co > Ni > Cr > Cd. The addition of SS, however, recorded a higher concentration of DTPA-extractable metals in soil over control. The heavy metals content did not exceed toxicity levels in soil and plants. Hence, the incorporation of SS (5 t ha−1) resulted in saving 25% mineral fertilizers and, also combined use of SS with mineral fertilizers proved to be economically beneficial for crop production.

Sewage Sludge Impacts on Yields, Nutrients and Heavy Metals Contents in Pearl Millet–Wheat System Grown Under Saline Environment

Drip irrigation and mulching are often used to alleviate the problem of poor water management in many crops; however, these technologies have not yet been tested for applying water at critical stages of guava orchard growth in subtropical humid Tarai regions of India to improve the yield and quality. A field experiment was conducted over 2020 and 2021 which included three irrigation strategies: severe deficit irrigation (DI50), moderate deficit irrigation (DI75), and full irrigation (FI100), as well as four mulching methods: silver-black mulch (MSB), black mulch (MB), organic mulch (MOM), and a control without mulch (MWM). The results showed that both the relative leaf water content (RLWC) and the proline content exhibited an increasing trend with a decrease in the irrigation regime, resulting in a 123% increase in the proline content under DI50 conditions compared with FI100, while greater plant growth was recorded in fully irrigated plants and using silver-black mulch. Leaf nutrient analysis showed that FI100 and MOM produced significantly higher concentrations of all nutrients. However, moderate deficit irrigation (DI75) along with silver-black mulch (MSB) produced higher numbers of fruits per plant, higher average fruit weights, higher fruit yields, and maximum ascorbic acid contents. The irrigation water productivity (IWP) decreased with an increase in the irrigation regime; from severe water deficit to full irrigation, resulting in a 33.79% improvement in IWP under DI50 conditions as compared with FI100. Regression analysis outperforms principal component regression analysis for fruit yield prediction, with adjusted R2 = 89.80%, RMSE = 1.91, MAE = 1.52, and MAPE = 3.83. The most important traits affecting the fruit yield of guava, based on stepwise regression, were leaf proline, leaf Cu, fruit weight, and IWP.

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Raj C. Popat

Papers

Sewage Sludge Impacts on Yields, Nutrients and Heavy Metals Contents in Pearl Millet–Wheat System Grown Under Saline Environment

Deficit irrigation scheduling with mulching and yield prediction of guava (Psidium guajava L.) in a subtropical humid region