Boron and zinc fertilizer applications are essential in emerging vegetable‐based crop rotations in Nepal

Abstract

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.

Residual effects of B and Zn fertilizers applied to dry season crops on the performance of the follow‐up crop of maize in Nepal

“…At the same time, Zn uptake was higher in non‐fertilized maize grown in soils with prior tomato and wheat cultivation, compared to cauliflower. These results are fully in line with the known high Zn demand of cauliflower ( Singh et al, 2012), and the previously observed lower Zn uptake by wheat and tomato compared to cauliflower ( Shrestha et al, 2020b).…”

“…It should be kept in mind that cauliflower, which is known to have a rather high B requirement ( Kotur , 1991), received here a total of 4.4 kg B ha −1 compared to 2.2 kg B ha −1 for tomato. The relatively low amounts of B applied to tomato were largely absorbed by the crop ( Shrestha et al, 2020b), leaving little residual B left in the soil for inducing possible carry‐over effects in maize. On the other hand, more B was left in the soil after wheat (with a very low B demand: Gupta , 2007; Wimmer et al, 2015) and cauliflower (with a larger supply), which could be taken up by the follow‐up maize in the Fluvisol.…”

“…In total, 48 treatment combinations, comprising 2 soil types × 2 systems × 3 dry season crops × 4 fertilizer treatments, were arranged in a completely randomized design using 4 replications (in total 192 pots). Further details regarding treatment applications are reported in Shrestha et al (2020b).…”

“…Total B and Zn uptake was calculated by multiplying the B and Zn contents (mg kg −1 ) of the dry biomass with the respective dry weight (mg pot −1 ) of the plants. More details on all analytical steps and procedures have been reported previously ( Shrestha et al, 2020a, 2020b). Data were analyzed using “stata” version 14.2”.…”

“…Similarly, B deficiency is a major constraint to many crops ( Shorrocks , 1997) in at least 80 countries worldwide ( Sillanpää , 1982), but it is particularly cumbersome in Nepal ( Shorrocks , 1997; Rerkasem and Jamjod , 2004). Hence, matching the in‐season demands for these micronutrients with targeted supplies of B and Zn is likely to enhance both crop production and product quality as has been shown recently for the emerging vegetable‐based rotation systems of Nepal ( Shrestha et al, 2020b).…”