Sugar beet (Beta vulgaris L.) response to diammonium phosphate and potassium sulphate under saline–sodic conditions Z. H USSAIN 1 , R. A. K HATTAK 2 , M. I RSHAD 3 & Q. MAHMOOD 3 1 Department of Development Studies, COMSATS Institute of Information Technology (CIIT), Abbottabad, Pakistan, 2 CECOS University of Information Technology and Emerging Sciences, Hayatabad Peshawar, Khyber Pakhtunkhwa, Pakistan, and 3 Department of Environmental Sciences, CIIT, Abbottabad, Pakistan Abstract Salinity and sodicity are prime threats to land resources resulting in huge economic and associated social consequences in several countries. Nutrient deficiencies reduce crop productivity in salt-affected regions. Soil fertility has not been sustainably managed in salt-affected arid regions. Few researchers investigated the crop responses to phosphorus and potassium interactions especially in saline–sodic soils. A research study was carried out to explore the effect of diammonium phosphorus (DAP) and potassium sulphate (K 2 SO 4 ) on sugar beet (Beta vulgaris L.) grown in a saline–sodic field located in Kohat district of Pakistan. The crop was irrigated with ground water with EC iw value of 2.17–3.0 dS/ m. Three levels each of K 2 O (0, 75 and 150 kg/ha) as K 2 SO 4 and P 2 O 5 (0, 60 and 120 kg/ha) as DAP were applied. The application of P significantly affected fresh beet and shoot yield while K fertilizers had significant effect on fresh beet yield and ratio of beet:shoot, while non-significant effects on the fresh shoot were observed. The application of K 1 and K 2 promoted sugar beet shoot yield by 49.2 and 49.2% at P 1 and 64.4 and 59.7% at P 2 , respectively over controls. In comparison with controls, fresh beet yield was increased (%) by 15 and 51, 45 and 84, and 50 and 58 for corresponding K 1 and K 2 at P 0 ,P 1 and P 2 , respectively. Addition of P 1 and P 2 increased beet yield by 37 and 47% over control. The shoot [P] (mmol/kg) were achieved as 55.2, 73.6 and 84.3 at P 0 ,P 1 and P 2 , respectively. The shoot [Mg] and [SO 4 ] tended to decrease with increasing P levels, while [SO 4 ] was markedly reduced at P 2 . The effect of P on leaf [Na] was non-significant, but increasing levels of K decreased [Na] substantially at P 0 and P 1 , but there was no difference in the effect of K level on [Na] at P 2 . Consequently, K application reduced leaf Na:K ratios. Fresh shoot yield was weakly associated with leaf [P] (R 2 = 0.53). The leaf Na:K ratio showed a negative relationship (R 2 = 0.90) with leaf [K]. A strongly positive relationship (R 2 = 0.75) was observed between leaf [K] and fresh beet yield. The addition of K 2 SO 4 also enhanced [SO 4 ] and SO 4 :P ratios in leaf tissues. The ratio of Na:K in the shoot decreased with increasing K application. These results demonstrated that interactions of K and P could mitigate the adverse effects of salinity and sodicity in soils. This would contribute to the efficient management of soil fertility system in arid-climate agriculture. Keywords: Potassium, phosphorus, salt-affected soils, sugar beet, yield, plant tissues, chemical analysis, post-harvest soil analysis Introduction Saline soils are characterized by the presence of higher salt contents in the soil or its solution which seriously hampers the crop productivity (Mass & Hoffman, 1977). Salinity is a menace not only for the aesthetic value of the land, but also renders soils unfit for plant growth. It results from the accumulation of either naturally occurring salts or caused by salts carried by runoff and irrigation water. It was estimated that about 23 and 37% of the world cultivated soils were saline and sodic, respectively (Szabolcs, 1989). Kovda & Correspondence: M. Irshad. E-mail: mirshad@ciit.net.pk Received September 2013; accepted after revision May 2014 © 2014 British Society of Soil Science 1 Soil Use and Management doi: 10.1111/sum.12132