Legumes play critical dual roles in grazed grassland ecosystems; providing nitrogen inputs and high-quality feed for grazing livestock. However, many species fail to persist in acidic, low fertility soils. A glasshouse study was conducted to investigate the response of lucerne (Medicago sativa) to phosphogypsum (PG), lime and soluble P + S fertilizer (PS) application to two soils. Phosphorus and sulphur were applied through either PG (0, 1, 3 and 9 t ha−1) or P + S fertilizer at equivalent rates to PG. Both PG and PS were applied with or without lime, which was applied at 2 t ha−1. Yield and nutrient uptake of the lucerne was measured, while the soil was analyzed for pH, Olsen P and exchangeable aluminum. Yield responses were significantly different between the two soils. Maximum yields and P and S uptakes were obtained under PG 9 t ha−1 combined with lime. Exchangeable Al decreased in both soils under 1 ha−1 of PG compared with the control. At the highest rate, Olsen P increased by 8 and 6 mg kg−1 for PG and by 6 and 11 mg kg−1 for PS compared with the control for Glenmore and Molesworth soils respectively. Phosphogypsum showed positive effects on P and S bioavailability.

In this work, we modelled the response of soil water repellency (SWR) persistence to the decrease in moisture in drying soils, and we explored the implication of soil particle size distribution and specific surface area on the SWR severity and persistence. A new equation for the relationship between SWR persistence and soil moisture (θ) is described in this paper. The persistence of SWR was measured on ten different hydrophobic soils using water drop penetration time (WDPT) at decreasing levels of gravimetric water content. The actual repellency persistence showed a sigmoidal response to soil moisture decrease, where Ra(θ)=Rp/1+eδ(θ−θc). The suggested equation enables one to model the actual SWR persistence (Ra) using θ, the potential repellency (Rp) and two characteristic parameters related to the shape of the response curve. The two parameters are the critical soil moisture θc, where the Ra increase rate reaches its maximum, and the parameter δ affecting the steepness of the curve at the inflexion point of the sigmoidal curve. Data shows that both soil carbon and texture are controlling the potential SWR in New Zealand pastures.

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