20 IREC Farmers' Newsletter No. 198 — Spring 2017 potential grain yield, all influence the ability of a variety to stand up at maturity, even with high grain yields. Data collected in the 2015–16 and 2016–17 seasons show that rice varieties that are more prone to lodging are generally taller in stature and have thinner stems, as shown by decreased stem weight per cm (Table 1). Varieties such as Doongara, Topazp and Reiziqp are relatively tolerant to lodging, while Koshihikari and YRK5 are highly susceptible (Table 1). When growing varieties that are more susceptible to lodging it is important to use all available management options to reduce the lodging potential of the crop. Sowing method Aerial sown crops are more prone to lodging than drill sown crops, and crops with delayed permanent water are the most tolerant to lodging. Better lodging resistance under drill sowing is due to better root anchorage in the soil and resistance against stem bending and breaking. Water management also affects lodging resistance as crops that are fully flooded from germination grow taller and have thinner stems than rice crops grown with intermittent irrigation during the establishment and tillering period. Plant density Although research has shown grain yield potential of rice to be the same between plant densities of 40 and 400 plants/m2 , higher plant densities can lead to increased lodging. Recent research on YRM70 and YRK5 varieties showed that higher plant densities (150 kg/ha seed resulting in about 250 plants/m2 ) tend to be more prone to lodging than lower plant densities (50 kg/ha seed resulting in about 100 plants/m2 ). Lodging in the higher sowing rate areas was considerably worse than in the lower rate areas (see photos above). To reduce lodging potential, it is important not to use higher than recommended sowing rates, especially for the small grain varieties, which have many more seeds per kilogram. Recommended sowing rates for rice varieties based on seed size and average varietal establishment percentages from field experiments are presented in Table 2. The smaller seed varieties (e.g. Opusp ) have more seeds per kilogram so should be sown at a lower rate to achieve the same plant population. Nitrogen rate and timing Nitrogen is very important in achieving high grain yields but excessive nitrogen applied pre-permanent water increases lodging, especially for lodging-susceptible varieties. Higher nitrogen rates result in increased lodging susceptibility in rice, due to increased tiller numbers, the length of lower internodes, plant height and reduced lower stem cellulose and lignin content, which reduce straw breaking strength and bending stress. Table 1. Average lodging score, plant height and stem weight for current rice varieties. Samples collected from several research experiments in the 2015–16 and 2016–17 seasons. Variety Lodging score (1=standing, 10=fully lodged) Plant height (cm) Stem weight (g/cm) Doongara 1.0 75 0.028 Topazp 1.0 81 0.022 Reiziqp 1.1 80 0.024 Sherpap 1.2 83 0.022 Opusp 2.0 81 0.022 Langi 2.1 86 0.022 Illabong 2.4 86 0.022 YRM70 2.6 85 0.019 Jarrah 4.2 85 0.021 YRK5 5.6 93 0.018 Koshihikari 6.1 91 0.018 Table 2. Sowing rates to meet plant population recommendations, based on seed size and average varietal establishment percentage. Variety Sowing rate (kg/ha) Reiziqp , Illabong & Topazp 150 Sherpap , Langi, Doongara & YRM70 130 Opusp , Koshihikari & YRK5 120 YRK5 drill sown at sowing rates of 50 kg/ha (left) and 150 kg/ha (right) and fertilised with 200 kg/ha urea applied before permanent water.