Responses of sulfur, nitrogen and irrigation water on Zea mays growth and nutrients uptake.(Report)

Introduction

Major agricultural soils in United Arab Emirates (UAE) are dominated by sandy calcareous type which is relatively low in organic matter content with high pH value that showed marked influence on the nutrients availability for plant growth (Abdou, 2006). Soil pH has an important role in the loss of N and or fixation of most nutrients and therefore different nutrient management practices are required for crop production in calcareous and non-calcareous soils. Calcareous soil has high Ca[CO.sub.3] and alkaline pH that greatly reduce the solubility of Fe, Zn, Mn, and Cu thus characterizing as deficient in these micro nutrients. The presence of Ca[CO.sub.3] in soils also directly or indirectly affects the availability of N, P, Mg, and K (Brady and Weil, 2002). Additions of [S.sup.0] are used as a nutrient and acidifier which can alter physicochemical properties of soil (Neilson et al., 1993). The biochemical oxidation of [S.sup.0] produces [H.sub.2][So.sub.4] which decreases soil pH and solubilizes Ca[CO.sub.3] in alkaline calcareous soils to make soil conditions more favorable for plants growth including the availability of plant nutrients (Lindemann et al., 1991; Abdou, 2006; El-Tarabily et al., 2006). Nitrogen, P and K are frequently the most limiting nutrients for plant growth in numerous ecosystems (Olivera et al., 2004). Intensive cropping systems requires important amounts of N, P, K and S fertilizers and among these N fertilizer plays significant role. Crop deficiencies of S have been reported with increasing frequency in the last decade, caused by decreasing anthropogenic S input and by the lack of input through S fertilization to compensate for exportation (Scherer, 2001). Sulfur is accumulated in plants in low concentrations compared to N, but is an essential element as a constituent of proteins, Cysteine-containing peptides such as glutathione, or numerous secondary metabolites (Scherer et al., 2008; Abdallah et al., 2010). Sulfur deficiency can reduce NUE and that N deficiency can also reduce S-use efficiency (Fismes et al., 2000). Nitrogen and S both involved in protein synthesis and play an

important role in the protection of plants against nutrient stress and pests (Luit et al., 1999) and synthesis of vitamins and chlorophyll in the cell (Kacar and Katkat, 2007). The severity of S deficiency is aggravated by higher rates of N application. Plants grown without N fertilizer showed no apparent S stress, whereas plant receiving N fertilizer, particularly at higher rate without S, showed symptoms suggesting severe physiological disorder in N nutrition (Janzen and Bettany, 1987; Kopriva and Rennenberg, 2004). Increased application of N fertilizer increasing S response resulting its N/S ratio leading to a reduction of protein-N and an increase in nitrate-N and other non-protein N fractions and crop quality may adversely affected (Jackson, 2000). Seed yield decreased due to insufficient supply of S nutrition while an excessive supply of S can affect quality of meal by increasing glucosinolates content in seed (Rosa and Rodrigues, 1998). The poor efficiency of N caused by insufficient S needed to convert N into biomass may increase N losses from cultivated soils (Schnug et al., 1993; MacGrath and Zhao, 1996). Conversely, N addition increased seed yield in S-rich conditions, and maximum yield responses to both N and S applications are obtained when the amounts of available N and S are balanced (Joshi et al., 1998). Corn as an oilseed crop is highly responsive to S; making corn an ideal crop for S application in the forms of [S.sup.0] and ammonium sulfate or urea, especially in alkaline and calcareous soils (Ghosh et al., 2000). Nutrients availability and uptake ability in calcareous soil can be enhanced by acidification which has large cumulative effects on the overall N balance and amount of soil N reserves (Cassman et al., 2002). Sulfur uptake efficiency is increased and deficiency symptom is disappeared by the application of N fertilizer in the form of urea in S deficient soil (Murphy, 1999). The interaction of nutrients is of great importance because decline in S supply from the atmosphere has already caused substantial losses of N from agro-ecosystems to the environment (Luit et al., 1999). Therefore, a strong focus on reducing N leads to arid environments and the interaction between N and S metabolism needs more clarification with a view to improve environment friendly fertilizing techniques. Based on these observations, sufficient supply of S is required to maintain the optimum growth and nutrient uptake ability of plants. For this purpose, the use of [S.sup.0] fertilizer is gaining importance, because besides the inhibitory actions on N, it contains high S concentration. Substantial information on N and S nutrition of plant is available (Fismes et al., 2000) but the data related to both N and S interaction with irrigation water either acidified or normal are still insufficient, especially for corn cultivation in sandy calcareous soils of UAE. Accounting for the above observations, this research was undertaken to investigate the impact of increasing levels of [S.sup.0] fertilization on N and S utilization, growth and nutrient uptake ability of corn grown in sandy calcareous soil with acidified and normal irrigation water.

Materials and methods

Experimental design

Greenhouse experiments were conducted at Al-Foah Agricultural Experiment Station (27[degrees]N and 22[degrees]S latitude and 51[degrees]W and 57[degrees]E longitude), UAE University in 2005. Elemental S at rates of 0, 1, 5 and 10 t [ha.sup.-1] were tested combined with or without N at rates of 0 and 0.34 t [ha.sup.-1] in pots under evaporative cooled greenhouse conditions. The treatment arrangements are as follows: S 0+N 0 (control), S 0+N 0.34 t [ha.sup.-1], S 1 t [ha.sup.-1]+N 0, S 1 t [ha.sup.-1]+N 0.34 t [ha.sup.-1], S 5 t [ha.sup.-1]+N 0, S 5 t [ha.sup.-1]+N 0.34 t [ha.sup.-1], S 10 t [ha.sup.-1]+N 0, S 10 t [ha.sup.-1]+N 0.34 t [ha.sup.-1]. The experiment was laid out in a factorial completely randomized design with three replications. With same set of treatments, four experiments were carried out simultaneously using each with normal (pH >7.5) and acidified irrigated water (pH 6.5), respectively in Al Zaid and Al Semaih soils. Sandy calcareous soil was collected from the areas of Al Zaid and Al Semaih in Abu Dhabi, UAE. Based on the name of soil collection sites, tested soils were designated as Al Zaid and Al Semaih soils. A proportion of soil was separated and sieved through 1-mm stainless steel sieve and stored in plastic bags for physicochemical analysis. Soil pH was determined from the prepared soil suspension (1:2.5 soil water ratios) by using combined pH meter model 900A (Thermo Orion, Ontario, Canada) (Thomas, 1996). Electrical conductivity (EC) was measured by the saturation extracts of soil samples using Orion model 120 microprocessor conductivity meters (Thermo Scientific, USA). Water soluble cations (Ca, Mg, Na, and K) and anions (Cl, H[CO.sub.3], [CO.sub.3] and [So.sub.4]) were determined as per the methods recommended …