‘On-farm’ seed priming with zinc sulphate solution—A cost-effective way to increase the maize yields of resource-poor farmers

The effect of adding zinc sulphate (ZnSO4) to maize (Zea mays L.) growing on calcareous, Zn deficient soils in the North West Frontier Province of Pakistan was assessed in vitro, on-station and in on-farm trials. The zinc sulphate was added either as a powder to the soil or by soaking seeds for 16 h in dilute solutions prior to sowing. For the first time in maize, we separated the benefits of priming simply with water from those provided by added zinc.In four trials, the soil application of 2.75 kg Zn ha−1 significantly increased mean maize grain yield by 720 kg ha−1 (25%) total dry matter, number of cobs and cob weight. Adding 5.50 kg Zn ha−1 was the same as adding 2.75 kg Zn ha−1 for TDM and cob yield but worse for cob number and grain yield.Preliminary experiments established that maize seeds could be primed safely and effectively for 16 h with 1% Zn solutions. Such priming increased seed Zn content initially from 15 mg kg−1 to 560 mg kg−1 but this was reduced to 220 mg kg−1 by rinsing the seed surface with distilled water. Non-rinsed seeds were used in all field trials. Seedlings from seeds primed with either 1% or 2% Zn were significantly heavier and taller than seedlings from non-primed seeds. The Zn concentration of seedlings was unaffected by priming with water alone but was increased significantly by both Zn priming treatments. The amount of Zn per plant was further increased because priming and Zn supply produced bigger plants.In seven further trials, mean grain yield was significantly increased from 3.0 t ha−1 in crops from non-primed seed to 3.4 t ha−1 (14%) in crops from seeds primed with water alone and to 3.8 t ha−1 (27%, a similar response to that following soil application) using seeds primed with 1% Zn. Hence, the contribution of water alone and zinc contributed about equally to the overall increase. Total dry matter, stover dry matter, cob yield, individual cob weight, grain number per cob, cob number and 1000-grain weight showed similar responses to that of mean grain yield. Plant population density and shelling percentage were unaffected by either treatment. Grain Zn concentration was 15.4 mg kg−1 in a non-primed crop and was significantly higher in a crop grown from seeds primed with water (16.5 mg kg−1) and with 1% Zn (18.3 mg kg−1). The apparent recovery of added Zn in the grain was much higher for seed priming (at around 80%) than the less than 1% for soil fertilisation.Monetary returns to use of ZnSO4 were high, with a benefit to cost ratio for soil application of 15. However, the ratio was much higher, at 236, when a 1% Zn solution was used to prime seeds before sowing. This was due to the small amounts of ZnSO4 used per hectare and hence low cost. Since priming maize seeds with water increased yield by 14% at no extra cost and adding small amounts of ZnSO4 to the priming water doubled that yield gain, priming with 1% Zn represents an attractive option for resource-poor maize farmers in Zn-deficient areas in Pakistan and elsewhere.