Agronomic Efficiency of Polyhalite Application on Peanut Yield and Quality in Vietnam.

ABSTRACT

Peanut (Arachis hypogaea L.) has an important role in traditional crop rotation in Vietnam, and particularly in Binh Dinh province, where the planting area ranges from 8,300-10,200 ha, and the average yield increased by 12%, from 2.67 to 2.99 Mg ha–1 during 2009 to 2014. The sandy (97%) acidic (pH 5.1) soils in this humid tropical climate require careful balanced fertilization that should support a sustainable cropping system and provide sufficient profits to the farmers. As peanut is a legume, small rates of nitrogen (N) are required but adequate sulfur (S) and potassium (K) rates are essential to obtain considerable yields.Polyhalite, a sedimentary marine evaporate, consists of a hydrated sulfate of K, calcium (Ca) and magnesium (Mg) with the formula: K2Ca2Mg(SO4)4·2(H2O), which contains 48% S. The objectives of this study are to evaluate the effects of K and polyhalite application rates on peanut agronomic and economic performances and to suggest an optimum fertilization mode for the growing conditions in the Central Coast of Vietnam. Six fertilization treatments were tested: Farmers’ practice (FP) control, with N:P:K ratio of 95:40:100; NP-K0, with 45 kg N ha–1, 90 kg P2O5 ha–1, and zero K; and NP-K30; NP-K30-S1; NP-K60-S2, and NP-K90-S3, all of which were applied with similar N and P rates, K rates increasing from 30 to 90 kg K2O ha–1, and polyhalite at 107 (S1), 214 (S2), and 321 kg ha–1 (S3), respectively. FP and NP-K0 displayed the poorest performance in most parameters tested and obtained low peanut yield and benefit. The optimum treatment was achieved with NP-K60-S2, which resulted in 2.86 Mg ha–1 of grains, 24% more than the FP control, and in a 98% increase in the net benefit to the farmer. A further increase in K and S rates did not provide any further advantage. Soil examinations, before sowing and after harvest, indicated that while FP significantly reduced soil fertility, employing polyhalite to create a balanced N-P-K-S management led to enhanced soil fertility, thus supporting a sustainable cropping system.

Keywords: Acidic soils; Arachis hypogaea L.; Polysulphate; potassium; sulfur.