The effects of olive mill waste compost and poultry manure on the availability and plant uptake of nutrients in a highly saline soil

Abstract

The effects of a compost (produced from by-products of the olive oil industry) and a poultry manure on mineral ion solubility and exchangeability in a highly saline agricultural soil (electrical conductivity for a 1:5 soil:water extract = 1.85 dS m⁻¹) from Murcia (SE Spain) were studied. The organic amendments did not change significantly the soil electrical conductivity or the soluble Na⁺, Ca²⁺ or Mg²⁺. Only soluble K⁺ increased, due to the K⁺ supplied by the amendments. The cation exchange capacity increased in treated soils, the exchange complex being mainly saturated with Ca²⁺, Mg²⁺ and K⁺. However, Na⁺ was not retained in the exchange sites, and the sodium absorption ratio remained low. The compost and manure increased markedly the shoot growth of the salt-tolerant Beta maritima L. (sea beet) and Beta vulgaris L. (sugar beet). For B. maritima, this seemed to be related to decreases in the shoot concentrations of Na⁺ and Cl⁻ and increases in K⁺ and ${\text{H}}_2{\text{PO}}_4^{-}$. In the case of B. vulgaris, increases in shoot ${\text{H}}_2{\text{PO}}_4^{-}$ and B and, for manure-treated soil, a decrease in shoot Na⁺ may have been involved. Cultivation of tomato (Lycopersicon esculentum Mill. cv. Moneymaker) in the soil used previously for B. vulgaris indicated that the effects of the manure on tissue cation concentrations were longer-lasting than those of the compost.

Introduction

Within the region of Murcia (SE Spain), 200,000 ha of agricultural and horticultural crops are dependent upon irrigation, due to the prevailing conditions of low rainfall (<450 mm per year) and high evapotranspiration (>900 mm per year) (Schofield et al., 2001). Here, as in other Mediterranean regions, the widespread use of waters containing relatively high levels of dissolved salts (Lax et al., 1994, Schofield et al., 2001) together with high evaporation rates has led to the accumulation of salts (Ca²⁺, Mg²⁺, Na⁺, Cl⁻, ${\text{SO}}_4^{2-}$) in the surface soil layers (Schofield et al., 2001). In certain cases, this problem has been worsened by rises in the water table (Caro, 1970). The accumulation of salts in soil, particularly Na⁺ at the cation exchange surfaces, as reflected in the values of exchangeable Na⁺ percentage (ESP; >15% indicates sodic soil), worsens the soil physical conditions, with respect to aggregate formation, water infiltration and water-holding capacity (Lax et al., 1994). Plants growing in saline media generally exhibit tissue accumulation of Na⁺ and Cl⁻, and inhibition of uptake of mineral nutrients, especially Ca²⁺, K⁺, N and P (Marschner, 1995, Romero-Aranda et al., 2001, Ghoulam et al., 2002). The resulting mechanisms of growth inhibition include effects on gas exchange, photosynthesis and protein synthesis, in addition to the disturbance of plant water relations caused by the high osmotic potential of the external medium (Marschner, 1995, Carvajal et al., 2000, Romero-Aranda et al., 2001, Ghoulam et al., 2002).

For saline or sodic soils, the addition of organic matter (OM) can accelerate the leaching of Na⁺, decrease the ESP and the electrical conductivity (EC) and increase water infiltration, water-holding capacity and aggregate stability (Lax et al., 1994, Qadir et al., 2001). This is particularly important for agricultural soils deficient in OM, such as those in the Murcia region (1–3% OM). Also, by supplying nutrients, particularly N, P and K⁺, organic amendments can improve the mineral nutrient status and growth of plants grown in such soils (Lax et al., 1994, Qadir et al., 2001). Saline soils may possess phytotoxic levels of boron (B) (Marschner, 1995). The addition of OM to soil can increase B adsorption and, as a consequence, decrease the soil solution and plant tissue B concentrations (Yermiyahu et al., 2001), but, depending on its B content, OM can increase soil and plant tissue B levels (Sharma et al., 1999, Walker and Bernal, 2004). For animal manures or composts having relatively high salt contents, repeated applications and/or elevated application rates can exacerbate soil salinity, leading to structural breakdown and/or plant growth inhibition (Bernal et al., 1992b, Wong et al., 1999, Smith et al., 2001).

In Spain, the use of waste matter from the olive oil industry (following composting) and animal manures as soil amendments represents a strategy for the management of the high production of these materials, in which their plant nutrients and OM are returned to the soil. In the work described here, the effects of two organic amendments, a fresh poultry manure and a mature compost, on a highly saline soil were investigated. The changes in soil physico-chemical conditions were determined, as were effects on the growth and tissue levels of mineral nutrients (K⁺, Ca²⁺, Mg²⁺, ${\text{NO}}_3^{-}$, ${\text{H}}_2{\text{PO}}_4^{-}$ and B) and potentially toxic elements (Na⁺ and Cl⁻) for plants cultivated in this soil. The species used were the highly salt-tolerant Beta maritima L. (sea beet), a common crop in saline Mediterranean soils (Niazi et al., 2000, Bor et al., 2003), the relatively tolerant Beta vulgaris L. (sugar beet) (Maas, 1985, Katerji et al., 2000) and the less tolerant tomato (Lycopersicon esculentum Mill.) cv. Moneymaker (Romero-Aranda et al., 2001).