Effects of polyacrylamide (PAM) and gypsum on irrigated and dryland potatoes (Solanum tuberosum L.).
An experiment was conducted at Lincoln University to investigate the effects of irrigation, micronised polyacrylamide (PAM) and gypsum on the growth and yield of 'Ilam Hardy' potatoes in 2001-2002. At the final harvest, tuber yields were similar (59 500 kg ha⁻¹). Environmental factors dominated results, particularly January rainfall, which was 150% of the 16-year average. Economic yield (tubers> 113g) was not affected by any treatment and was >80% of total tuber yield. Premium size tubers (> 170g) were 65% of total tuber yields and no treatment affected tuber size distribution. The maximum crop growth rate was higher from irrigated (189 kg DM ha⁻¹ d⁻¹) than dryland plots (174 kg DM ha⁻¹d⁻¹). This reflected differences in leaf area index at two times during the later growth period. Mean crop growth rate, as a result, was also lower (118 kg DM ha⁻¹ d⁻¹) compared to irrigated plots (130 kg DM ha⁻¹ d⁻¹). The duration of growth was similar (125 days) for all treatments. There was no effect of any treatment on soil adherence to tubers. Aggregate stability was increased 24% by gypsum application. However, poor initial soil structure caused by years of intensive cultivation meant this only increased to 2.4% and was unlikely to have had any affect on crop growth and yield.... [Show full abstract]