Growth and phosphorus nutrition of rice when inorganic fertiliser application is partly replaced by straw under varying moisture availability in sandy and clay soils

The combined effects of (1) reduced soil moisture availability, (2) reduced application of inorganic fertilisers while incorporating straw, (3) soil type, and their effects on growth, root system plasticity, phosphorus (P) nutrition of rice, and soil P dynamics are poorly known, but very important when aiming to increase the efficiency of water and P use. Using large pots a three-factor factorial experiment was conducted with two moisture treatments (i.e. continuous flooding, and draining of top soil after flowering while subsoil was kept moist through capillary action), three fertilisation treatments; with (P1) and without (P0) applications of inorganic P fertilisers, and 25 % of inorganic fertilisers reduced while incorporating straw (5 t ha(-1)), and soil type (i.e. clay and sandy soils with 15 and 9 mg P kg(-1) soil, respectively in P0). Shoot and root growth, root system plasticity, P nutrient status and soil P dynamics were measured. Straw incorporation with reduced inorganic fertiliser application ensured a higher shoot dry weight and yield only in flooded clay soil as compared with P0 and P1, and a similar shoot dry weight and yield to P1 under drained clay soil. A positive growth response was facilitated by an increased water-use efficiency and rate of photosynthesis in shoots, and increased root system plasticity through the production of greater root length, more roots in deep soil layers, and an increased fraction of fine roots. Straw enhanced P extractability in soil. Drained soil reduced P uptake (15-45 %) and increased P-use efficiency. In addition to the re-translocation of P from senescing leaves and stems under both moisture conditions, the P concentration in green leaves under drained condition was also reduced (41-72 %). Growth benefits of straw incorporation were observed in clay soil under both moisture conditions, and this was facilitated by the improved P availability, increased P uptake, and greater root system plasticity with the production of deeper and finer roots, compared with that in sandy soil, and inorganic fertiliser applications alone. As P uptake was reduced under drained soil, P re-translocation and % P allocated to panicles increased.