Baseline assumptions for yield and health-based valuations were made using recent data from Pakistan for: (1) dietary Zn supply from wheat, grown with and without Zn fertilisers; (2) current Zn fertiliser practices and costs; (3) wheat production statistics and support prices; (4) estimated disease burden in terms of lost DALYs due to Zn deficiency. Data were obtained from published and unpublished sources, including a large-scale survey of farmer practices in Punjab and Sindh. The value of increasing Zn fertiliser-use from this baseline was estimated using scenario changes combined with explicit assumptions described below. The study focuses on Punjab and Sindh as the major agricultural production regions of Pakistan and because of data availability. The study focuses on wheat as the dominant dietary source of energy and Zn in Pakistan (FAO 2015).
Dietary Zn supply from wheat under baseline and Zn-fertilised scenarios
Recent published estimates of dietary energy supply from wheat, rice and other main food sources were obtained from Kumssa et al. (2015b). The supply of Zn for Pakistan was estimated to be 13.9 mg Zn capita
−1 d−1 in 2010 (Kumssa et al. 2015b; Fig. 1). This is based on FAO Food Balance Sheets for 2010 (FAO 2015), which report a supply of 311 g capita
−1 d−1 of wheat grain and USDA food composition data of 29.1 mg Zn kg−1 (USDA 2013). Wheat would therefore supply 8.3 mg Zn capita
−1 d−1 after correcting for edible portion (Supplementary Table 1). Wheat is the major staple food in Pakistan, contributing ~37 % of the daily energy in the Pakistan food supply system. The supply of rice is much less at 37 g capita d−1 (Fig. 1).
USDA data is likely to overestimate the Zn concentration of wheat grain grown on soils with low-Zn availability such as in Pakistan. Thus, we adjusted estimates of dietary Zn supply, using data from grain samples of wheat grown in Pakistan on soils of contrasting Zn status. Collection of these grain samples was described previously (Zia et al. 2015). The mean/median grain Zn concentration was 24.9/24.5 mg kg−1 (standard deviation = 4.8; range = 15.1–39.7, n = 75; Munir H. Zia and Michael J. Watts, unpublished observations). Using a mean grain Zn concentration value of 24.9 mg kg−1 represents a supply of 7.1 mg Zn capita
−1 d−1 from wheat for Pakistan in 2010, after correcting for edible portion, and a baseline dietary Zn deficiency risk of 23.9 % compared to 16.1 % based on USDA wheat composition data. Both estimates assume a national population-weighted Estimated Average Requirement (EAR) of 10.4 mg Zn capita
−1 d−1 (Kumssa et al. 2015b). These baseline estimates of dietary Zn deficiency are likely to underestimate the extent of nutritional Zn deficiency. For example, the 2011 Pakistan National Nutrition Survey Report (NNS 2011) reported that 42 % (n = 5953) and 48 % (n = 791) of non-pregnant and pregnant women respectively and 37 % (n = 2499) of children <5 years were Zn-deficient, based on having plasma Zn concentrations <60 μg Zn dL−1. This discrepancy is likely to be due to: (1) an over-estimate of dietary Zn supply, considering the use of USDA food composition data for food items other than wheat and considering that food supply data does not account for household-level wastage; (2) the assumption of a 25 % coefficient of variation in dietary Zn intakes may underestimate the inequality of access to food due to socio-economic or social exclusion factors (Joy et al. 2014, 2015a, b; Kumssa et al. 2015a, b; Kuper et al. 2015); and (3) nutritional Zn deficiency can occur despite adequate dietary Zn supply due to factors such as diarrhoeal disease.
Zn fertiliser practices and costs
Fertiliser-use is currently unbalanced in Pakistan. In 2012/13, total fertiliser availability was 3865 kilotonnes (kt; NFDC 2013). This comprised 2975 kt of N, 863 kt of phosphate (P2O5), and 27 kt of potash (K2O). The offtake (consumption, nutrient weight) of fertilizer during this period was 3621 kt, comprising 2853 kt N, 747 kt phosphate, and 21 kt potash. The difference between availability and offtake is the amount carried forward into the next fiscal year, i.e. 2013/14. Urea (CO(NH2)2; 46:0:0 NPK) comprised 84 % of total N fertilisers used in 2012/13 (NFDC 2013). In terms of nutrient weights, 2391 kt of N use was from urea, 112 kt was from calcium ammonium nitrate (CAN; 5Ca(NO3)2.NH4NO3.10H2O; ~26:0:0), 242 kt was from diammonium phosphate (DAP; (NH4)2HPO4; 18:46:0), 103 kt was from nitrophos (NP; 22:20:0), with much smaller amounts of N from NPK fertilisers of varying composition and <1 kt from monoammonium phosphate (MAP; NH4H2PO4; 11:52:0). The most widely used form of phosphate in Pakistan is DAP (NFDC 2013). In 2012/13, this comprised 83 % of total phosphate fertiliser-use. In terms of P2O5 nutrient weight, 619 kt of phosphate use was from DAP, with 103 kt from NP, and 16 kt from single superphosphate (SSP; Ca(H2PO4)2; 0:14–18:0). There is negligible use of phosphate from triple superphosphate (TSP; Ca(H2PO4)2. H2O; 0:46:0) or NPK sources. Similarly, there is minimal potash fertiliser usage of just 21 kt in 2012/13 (NFDC 2013). This included 8 kt of sulphate of potash (SOP; K2SO4; ~0:0:50), 3.6 kt of muriate of potash (MOP; KCl; ~0:0:60), and the rest as NPK fertilisers.
Data for micronutrient fertiliser-use in Pakistan are not widely available, although usage is undoubtedly low. Baseline Zn fertiliser-use data for the 2012/13 cropping season were obtained from NFDC (2013), however, these include data solely for Engro Fertilizer Ltd. (Fig. 2a, b; NFDC, 2013). Data from Fauji Fertilizer Company Ltd. are from 2014 (Fig. 2c, d; Munir H. Zia, unpublished data, Fauji Fertilizer Company Ltd., FFC, Rawalpindi). Other major companies such as Fatima Fertilizer Company have recently started selling Zn fertilisers but sales data are not yet available. Fauji and Engro are likely to represent >50 % of the current Zn fertiliser market in Pakistan. It can be concluded from these data sources that the current use of Zn fertilisers in Pakistan is low (Fig. 2). Estimated annual use of Zn products on wheat is 7300 t (i.e. ZnSO4. H2O equivalents, 33 % Zn). Product use comprises 5100 t ZnSO4. H2O which are applied to soils in granular or powder forms, and 10,700 t of liquid Zn, including both ZnSO4.H2O and chelated Zn forms which is equivalent to 2200 t of granular ZnSO4. H2O. This represents a granular:foliar Zn-use ratio of ~0.7:0.3. Zinc fertiliser-use, i.e. usage divided by area under wheat production, is therefore <<1 kg ha−1 for most districts in Pakistan. Input costs for Zn were assumed to be US$ 1600 t−1 ZnSO4.H2O (2015 value; Munir H. Zia, personal communication). This amount is the approximate amount paid by the farmer, which comprises the cost of the raw product received at the port (~50 % of the cost in 2015), plus other costs including product unloading, transport, packaging, administration, and profit margin. Zinc fertilisers are used most widely in Punjab and Sindh, with limited use elsewhere in Pakistan (Fig. 2).
Baseline data for on-farm Zn fertiliser-use were obtained for Punjab and Sindh from a survey of >2500 farmers taken in early 2015 (Waqar Ahmad, personal communication, Food and Agriculture Organization of the United Nations, FAO, Islamabad). As part of a broader study, farmers were asked to recall information including farm-size, major crop types and yields from the 2014 harvest (i.e. wheat, rice, cotton, sugarcane, maize, other). They were also asked to recall crop-specific fertiliser usage, in terms of urea and CAN use for N; DAP/MAP/SSP/NP use for P; MOP/SOP use for K; Zn and B use). In this way, data were obtained from 1193 and 1338 farmers in Punjab and Sindh Provinces, respectively. There were consistent positive relationships between N and P2O5 application rates and wheat yield (Fig. 3), confirming that these survey data are a useful proxy for this current study. For example, wheat yields increased from ~2 t ha−1 at the lowest N application rates, to 4.4 and 3.9 t ha−1 at an application rate of 92 kg N ha−1.
In Punjab and Sindh, 14.4 and 23.2 % of farmers, respectively, reported using Zn fertilisers on wheat. This corresponds to a total area receiving Zn fertiliser of 1.1 and 0.4 Mha in Punjab and Sindh, respectively. Among farmers reporting Zn fertiliser-use, the mean application rate was 4.8 kg ZnSO4.H2O ha−1, based on dividing this area by 7.3 kt. The mean wheat yield without Zn fertilisers was 4.0 and 3.1 t ha−1 in Punjab and Sindh Provinces, respectively (Fig. 4).
Wheat production data and support prices
Area under wheat production was derived from the Pakistan Agriculture Census, with 7.5 and 1.9 M ha in Punjab and Sindh provinces, respectively (PBS 2010; Table 1). The mean yield is 2.5 and 1.9 t ha−1 in Punjab and Sindh, respectively (PBS 2009), of which 90 % and 97 % is irrigated (PBS 2010). Output prices of wheat are based on a support price of US$ 312 t−1 (October 2015 value; Munir H. Zia, personal communication).
Table 1 Wheat yields and production for Punjab and Sindh Provinces, Pakistan. Data from Pakistan Bureau of Statistics (2010), which reports that 90 and 97 % of wheat is irrigated in Punjab and Sindh, respectively
Disease burden due to Zn deficiency
An estimated 323,214 DALYs were lost due to Zn deficiency in Pakistan in 2010 on the basis of dietary Zn deficiencies, the prevalence of stunting, and a total population of 182 M (Wessells and Brown 2012; Lim et al. 2012; IHME 2014; UNDP 2013). This is equivalent to 187 DALYs lost 100 k−1 population. Recent population data for Punjab and Sindh are not available in the public domain, however these provinces comprised 54 % and 22 % of national population in 1998 (PCO 1998) so their 2010 populations were estimated to be 92.9 M and 38.4 M, respectively. Thus, in 2010, 173,506 and 71,746 DALYs were lost pro rata
per annum in Punjab and Sindh, respectively. As dietary Zn supplies increase, we assume that DALYs lost due to Zn deficiency will decrease at the same rate as the national prevalence of Zn deficiency from a baseline of 24.3 % and 22.8 % in Punjab and Sindh, respectively, and assuming no additional food consumption (Supplementary Tables 3, 4).
Assumptions used to simulate increased Zn fertiliser-use
To estimate the value of potential increased Zn fertiliser usage, an instantaneous, area-based approach was adopted, with no time dimension or discounting factors. This is justified because Zn fertilisers could be deployed immediately by incorporating Zn with existing granular N fertilisers or pesticide/fungicide sprays. We assumed that the proportion of wheat fertilised at 4.8 kg ha−1 could incrementally increase from the current 14.4 and 23.2 % of the areas currently under wheat production in Punjab and Sindh, respectively, up to 100 % of these areas. The granular:foliar Zn fertiliser-use ratio of ~0.7:0.3, based on current industry estimates, was assumed to remain constant.
Grain yields were assumed to increase by 8 % and 14 % under Zn fertilisation in Punjab and Sindh, respectively, according to median data from the farmer survey (Fig. 4). These increases were both highly significant (Student's t-tests; P < 0.001). This represents an area-normalised potential yield increase of 9 % for Punjab and Sindh combined. These survey data are therefore consistent with median yield increases of 16 % following soil Zn application in six site-years in Pakistan (Zou et al. 2012) and 10–11 % from applications of Zn fertilisers to maize, rice and wheat in a recent global literature review (Joy et al. 2015b). The potential increases in grain Zn concentration in wheat resulting from granular and foliar Zn fertiliser-use were taken from this same review. From 15 studies of wheat, comprising 196 combinations of location, cultivar and application rate, granular (soil-applied) and foliar Zn fertilisers resulted in median increases in grain Zn concentration of 19 % and 63 %, respectively (Fig. 5; Joy et al. 2015b). We therefore assumed that granular fertilisers increased grain Zn concentration by 19 %, from a baseline of 23.6 mg kg−1 (i.e. the 24.9 mg kg−1 was adjusted to assume zero Zn fertilisation) to 28.1 mg kg−1, and that foliar fertilisers increased grain Zn concentration by 63 % to 38.5 mg kg−1. Thus, the weighted mean increase in grain Zn concentration under Zn fertilisation was assumed to be 32.2 %, giving a concentration of Zn-fertilised wheat grain of 31.2 mg kg−1. All calculations are presented in Supplementary Tables 2–4.
The value of one DALY was monetised using multiples of Gross National Income (GNI) per capita, converted to International Dollars (I$) based on purchasing power parity (GNIPPP). An I$ has the equivalent purchasing power as a US$ dollar in the US based on the 2011 International Comparison Program. A per capita GNIPPP in Pakistan of I$ 5110 (http://data.worldbank.org/indicator/NY.GNP.PCAP.PP.CD) was used based on data in October 2015.