8 IREC Farmers' Newsletter No. 199 — Autumn 2018 Fertiliser Fertiliser management is different for crops sown after rice compared with other rotation crops. After rice there is no residual nitrogen and phosphorus can become tied up following drainage, therefore fertiliser requirements are increased. Fertiliser rates at sowing that result in too much nitrogen with or near the seed will cause seed damage and result in reduced germination. Table 1 shows the maximum rate of di-ammonium phosphate (DAP) to be applied at sowing to ensure a safe nitrogen concentration near the seed, for a variety of row spacings. Potential yield shown in Table 1 is phosphorus limited, i.e. phosphorus is limited by the safe rate of DAP recommended to avoid nitrogen damage to the seed. At wider row spacings and for higher target yields, mono-ammonium phosphate (MAP) may be a better fertiliser choice to safely provide sufficient phosphorus; and then topdressing rates can be increased in order to supply adequate nitrogen. As a general rule, 4 kg of phosphorus is needed to produce one tonne of wheat but after rice this should be increased to 5 kg per tonne. Topdressing requirements Topdressing is very important in the wheat after rice system and early application is best but as with all crops it is important to first assess the crop’s yield potential. If there are more than 110–130 plants/m² then it is recommended to top dress as early as possible and before rainfall. Fewer plants than this does not warrant further investment. The second topdressing should occur mid to late tillering. The third top dress should occur during stem elongation but is only needed if there are more than 450 tillers/m² and the target yield is 6.0 t/ha or greater. Table 2 shows urea topdressing rates for a range of target yields. Irrigation Although there is plenty of soil moisture at the start of the season following a rice crop, it may still be necessary to irrigate wheat in spring. This is dependent on season and target yield but to ensure the crop does not become drought stressed, soil moisture should be monitored from August onwards. For more information on irrigation of wheat after rice refer to the article Wheat after rice – how many irrigations? by Brian Dunn, NSW DPI, in the IREC Farmers’ Newsletter, No. 190 — Autumn 2014, page 16. Increase productivity and profitability Growing wheat after rice is a great way to increase the productivity of the irrigated farming system and increase the return on capital invested in irrigation infrastructure. However, wheat after rice will not be suitable every year, which may be due to many factors and some that are uncontrollable. The key requirements for successful wheat after rice are: l sow wheat early and at high rates l topdress early l ensure good drainage throughout the season. If these steps can’t be achieved then don’t attempt to grow wheat after rice. For more detailed information on growing wheat straight after rice, read the NSW DPI Primefact 1617 Growing wheat straight after rice or type the following link into your browser www.dpi.nsw.gov.au/ agriculture/irrigation/irrigation/scheduling/growing-wheat-straight- after-rice Table 1. Nitrogen (N), phosphorus (P) and DAP rates for a variety of row spacings, showing the phosphorus-limited yield. Table 2. Urea topdressing rates (kg/ha) for wheat after rice, assuming 30 kg/ha nitrogen is applied at sowing. Row spacing N (kg/ha) P (kg/ha) DAP (kg/ha) P-limited yield (t/ha) 7” or 18 cm 33 37 185 7.4 8” or 20 cm 30 33 165 6.6 9” or 23 cm 26 29 145 5.8 10” or 25 cm 23 26 130 5.2 11” or 28 cm 20 22 110 4.4 Target yield (t/ha) First top dress (kg/ha) Second top dress (kg/ha) Third top dress (kg/ha) 4.0 140 140 - 5.0 180 180 - 6.0 150 150 150 7.0 180 180 180 Further information Alex Schultz M: 0429 952 854 T: 03 5881 9905 E: [email protected] W: www.dpi.nsw.gov.au A wheat crop that had yield potential of more than 5.0 t/ha but due to poor drainage only yielded 3.4 t/ha. PHOTO: NSW DPI