The worldwide agricultural enterprise is facing immense pressure to intensify to feed the world’s increasing population while the resources are dwindling. Fertilizers which are deemed as indispensable inputs for food, fodder, and fuel production now also represent the dark side of the intensive food production system. With most crop production systems focused on increasing the quantity of produce, indiscriminate use of fertilizers has created havoc for the environment and damaged the fiber of the biogeosphere. Deteriorated nutritional quality of food and contribution to impaired ecosystem services are the major limiting factors in the further growth of the fertilizer sector. Nanotechnology in agriculture has come up as a better and seemingly sustainable solution to meet production targets as well as maintaining the environmental quality by use of less quantity of raw materials and active ingredients, increased nutrient use-efficiency by plants, and decreased environmental losses of nutrients. However, the use of nanofertilizers has so far been limited largely to controlled environments of laboratories, greenhouses, and institutional research experiments; production and availability on large scale are still lagging yet catching up fast. Despite perceivable advantages, the use of nanofertilizers is many times debated for adoption at a large scale. The scenario is gradually changing, worldwide, towards the use of nanofertilizers, especially macronutrients like nitrogen (e.g. market release of nano-urea to replace conventional urea in South Asia), to arrest environmental degradation and uphold vital ecosystem services which are in critical condition. This review offers a discussion on the purpose with which the nanofertilizers took shape, the benefits which can be achieved, and the challenges which nanofertilizers face for further development and real-world use, substantiated with the significant pieces of scientific evidence available so far. Graphical Abstract

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Globally, ravine landscapes are considered among the world's most degraded ecosystems. Restoring ravines is considered a high priority item in the conservation programmes, and tree establishment augmented with appropriate soil and water conservation measures is the most sought-after restoration strategy. This study examined the impact of terracing and trenching on runoff, soil loss, and soil properties along with Sapota (Achras zapota) growth, fruit yield, biomass and carbon stock during 6 years (2010)(2011)(2012)(2013)(2014)(2015) in a degraded ravine land of Western India. The four soil and water conservation strategies tested were (1) bench terracing + Sapota (Bt),(2) bench terracing + Sapota with crop cultivation (BtCr), (3) continuous slope + Sapota (Sl), and (4) continuous slope + Sapota with trenches (SlTr). All conservation techniques increased Sapota height (Bt: 54%; BtCr: 27%; SlTr: 35%) and basal diameter (Bt: 36%; BtCr: 18%; StCr: 22%) compared to Sl. Biomass and carbon stock of Sapota were in the order of Bt > SlTr > BtCr > Sl. During the droughtperiod, fruit yield was highest in Bt followed by BtCr, SlTr, and least in Sl. The treatment SlTr and Bt reduced runoff by 16-34% and soil loss by 15-25%, compared to Sl. The growth and biomass were strongly correlated with soil loss. The findings suggested that bench terracing is the best soil and water conservation measure for restoring highly degraded ravines of Western India. Under circumstances where terracing is not feasible, trenching could be a significant step along with Sapota plantation to restore these ravines.

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