The potential of tagasaste (Chamaecytisus palmensis) in maintaining fertility in a sustainable cropping system

The effects of incorporating tagasaste (Chamaecytisus palmensis) dry matter (DM) on the growth and yield of maize (Zea mays L.) was studied in two field experiments in Canterbury, New Zealand. In the first experiment (1997-98), tagasaste DM was incorporated at four rates (0, 5, 10 and 15 t DM/ha) and maize was sown four (7 November) and eight (5 December) weeks after tagasaste incorporation. In the second experiment (1998-99), 0 and 10 t DM/ha of tagasaste and 200 kg N/ha were soil incorporated and maize was sown four weeks after tagasaste incorporation (2 November) with no, or with full irrigation. In 1997-98, the incorporation of 15 t DM/ha of tagasaste increased maize DM yield from 19,700 to 25,400 kg/ha and grain yield by 33%. This was equivalent to maize production from the plots which received 200 kg N/ha. The November sown crop produced 42% higher grain yield than the December sown crop. However, the DM yield did not differ with sowing date. Incorporating 15 t DM/ha increased both the weighted mean average growth rate and maximum crop growth rate by 26% but had no effect on the duration of exponential growth. Leaf area duration increased at 15 t DM/ha of tagasaste but sowing date had no effect. Maize sown in November intercepted about 17% more photosynthetically active radiation (PAR) but had a lower radiation use efficiency (RUE), than the December sown crop. Tagasaste incorporation at 15 t DM/ha increased RUE by 24% from 2.59 to 3.22 g DM/MJ PAR. Incorporating at least 10 t DM/ha of tagasaste reduced soil bulk density and increased total soil nitrogen but had no influence on the soil C:N ratio or pH in both seasons. In 1998-99, application of 200 kg N/ha reduced the soil pH. Volumetric soil water content at grain filling for the unirrigated plots was approximately 66% of the irrigated plots. Dry matter yield increased by 5,200 kg/ha with irrigation in 1998-99. Irrigation did not increase grain yield but, it did increase mean grain weight by 21%. Irrigation increased DM yield by increasing intercepted PAR from 730 to 860 MJ/m². There was a positive and linear relationship between DM accumulation and intercepted PAR and between DM and grain yield. There was a significant interaction between incorporation of tagasaste or 200 kg N/ha and irrigation for DM production. In irrigated plots, the DM yield from the 200 kg N/ha plots at 27,000 kg/ha was about 14% higher than the yield from plots where tagasaste had been incorporated. These plots produced 3,200 kg more DM/ha than the control plots. However, in the unirrigated plots, DM yields were similar in the 10 t DM/ha and 200 kg N/ha plots. Both treatments gave higher DM yield than the control. Incorporation of either 10 t DM/ha or 200 kg N/ha increased the DM and grain yield by increasing RUE. The results show that tagasaste incorporation can improve soil fertility and increase maize yield provided sowing date coincides with periods of adequate soil moisture.