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Background: Diversified food crop production systems with high‐value vegetable crops are increasingly replacing conventional rice–wheat rotations across Nepal. These newly emerging systems are likely to enhance the demand for the micro‐nutrients boron (B) and zinc (Zn), which are already widely deficient throughout in Nepal. However, B and Zn fertilizers often are either unavailable in rural areas, not available in a timely manner, or when available not affordable by smallholder farmers. Aims: To overcome multiple constraints concerning the need and efficient use of B and Zn amendments in a technical feasible way with a high financial efficiency for farmers and without compromising the environment, the current study assessed whether soil stock provisioning, e.g., B and Zn fertilizer applications to dry season crops, may provide sufficient residual effects for the succeeding non‐fertilized wet season crop. Methods: A pot experiment was conducted in a sheltered greenhouse using two contrasting but representative soil types (Acrisol and Fluvisol) collected from rice‐ and from maize‐based production systems in Nepal. Boron and Zn amounts were supplied individually or in combination to wheat, cauliflower, and tomato grown in the dry season of 2018, whilst measuring biomass accumulation, B and Zn concentrations in plant tissues of all crops which allowed calculating B and Zn uptake in the unfertilized follow‐up crop of maize. Results: Soil‐applied B and Zn fertilizers, sole and combined, slightly enhanced biomass of the succeeding non‐fertilized maize only, but significantly increased total B and Zn plant uptake, with significant differences between soil types. Furthermore, while maize shoot B concentrations were consistently increased above the critical levels in both soils, but especially in the Fluvisol after wheat and cauliflower pre‐crops, Zn uptake of maize was more enhanced in the Acrisol. Conclusions: The residual effects of B and/or Zn applied to preceding dry season crops benefitted the subsequent wet season maize, especially after the pre‐crops wheat and cauliflower in the Fluvisol for B, and after wheat and tomato in the Acrisol for Zn. They may suffice to attain reasonable yields of wet season crops in the emerging vegetable‐based cropping systems of Nepal, even if fertilizers are not consistently available. The magnitude of the residual effects of pre‐applied Zn largely depended on the soil type, while those of B were mainly determined by the pre‐crop. [ABSTRACT FROM AUTHOR]

Background: Since recently, the traditional rice–wheat rotation systems in Nepal are subject to drastic changes. Progressing urbanisation and shifting consumer preferences drive a replacement of wheat by high‐value vegetables during the cold dry season, particularly in the peri‐urban fringes, while emerging water shortages prevent permanent soil flooding during the monsoon season, leading to partial substitution of lowland rice by less water‐consuming upland crops. Associated changes in soil aeration status affect soil nutrient availability while particularly vegetables enhance the demand for the critically limiting micronutrients boron (B) and zinc (Zn). Aim: In both rice‐ (anaerobic) and maize‐based (aerobic) systems we assessed the differential response of traditional winter wheat in comparison to cauliflower and tomato to applied B and Zn fertilizers. Methods: Experiments were conducted (1) in a pot trial with two contrasting soil types (Acrisol vs. Fluvisol) and (2) in field validation trials at two contrasting sites (representing lowland vs. mid‐hills) in Nepal. Results: The on‐going shift from flooded rice to aerobic maize during the wet season negatively affected dry matter accumulation and grain yield of the dry season wheat, but not of cauliflower and tomato. While Zn application tended to increase wheat yields under field conditions, B application induced no significant effect, irrespective of the soil or production site. However, low to moderate applications of B (2.0–4.4 kg ha−1) and Zn (3.3–4.4 kg ha−1) nearly doubled biomass accumulation and nutrient uptake of vegetables and increased the economic yields of cauliflower and tomato between 8 and > 100%. These responses were generally more pronounced in the Fluvisol than the Acrisol. While overall yields of wheat and temperate vegetables were higher in the cool mid‐hills the relative yield responses to applied B were more pronounced in the lowland than the mid‐hill sites. On average, the partial factor productivities of applied fertilizer were low to moderate in wheat, with 1 and 8 € increase in net revenue per € of investment in B and Zn, respectively. In the vegetables, this partial factor productivity increased to about 4 € €−1 investment with Zn, and reached about 43 € €−1 investment in B, irrespective of the production site. Conclusions: While the application of Zn fertilizers can moderately improve the performance of traditional rice–wheat rotations, B and to a lesser extent Zn application become essential and highly profitable when shifting towards vegetable cropping. The demand for B and Zn fertilizers is foreseen to dramatically increase with progressing urbanisation and the associated shifts in production systems of Nepal. [ABSTRACT FROM AUTHOR]

Background: Nepal's traditional rice–wheat rotation systems are subject to continuing changes. Changing consumer demand currently drives a replacement of wheat by high‐value vegetables during the dry season, while emerging water shortages lead to a substitution of rice by maize in the wet season. Hence, associated changes in soil aeration status and shifting conditions of soil nutrient supply to match crop nutrient demand are expected to increase the requirements for the principle limiting micro‐nutrients such as boron (B) and zinc (Zn). Aim: Our aim was to investigate the changes in B and Zn availability as well as crop yields and nutrient uptake after system shifts from rice to maize and from wheat to vegetables. Method: We analyzed the B and Zn availability in rice‐ and maize‐based systems as well as crop yields and the nutrient uptake by wheat, cauliflower, and tomato during the dry season in Nepal. Plants were grown at two field sites (midhills vs. lowland) and under greenhouse conditions using soils from the field sites. Results: A change from irrigated rice to maize reduced soil C and N contents with resulting decreases in dry season crop yields. Low soil Zn after rice cultivation led to shortage in Zn uptake by vegetables in both greenhouse and field experiments. The shift from wheat to vegetables increased the demand for B and to a lesser extent for Zn, and consequently vegetables showed visual symptoms of B deficiency. Boron concentrations in dry biomass were below the critical limits with < 10 mg B kg−1 in wheat, < 21 mg B kg−1 in cauliflower, and < 23 mg B kg−1 in tomato. Conclusions: Soils in larger parts of Nepal are low in available B and that the ongoing system shifts increase in the demand for B and Zn in the currently emerging and more diversified production systems. [ABSTRACT FROM AUTHOR]