Dynamic of cocksfoot urine patches in a silvopastoral system in New Zealand.

PERI P.L; LUCAS R.J.; MOOT D.J.

Orlando, Florida, USA

Congreso; 1st World Congress of Agroforestry, Session VI Tree Domestication and Management; 2004

University of Florida

Dry matter (DM) production and crude protein (CP) of sheep urine patches in a grazed cocksfoot (Dactylis glomerata) pasture (28 day rotation with 21¡¾1 days regrowth) under 10-11 year-old radiata pine (200 stems/ha) were measured over time at the Lincoln University Silvopastoral Experiment (Canterbury, New Zealand). Cocksfoot interactions with environmental conditions were evaluated using a leaf photosynthesis model. The area of cocksfoot pasture covered by urine patches ranged from 25 to 32%. The mean rate of nitrogen (N) applied per hectare in an individual urine patch ranged from 221 kg N/ha in autumn to 445 kg N/ha in spring. The mean DM production of new, individual urine patches ranged between zero and three times more than for non-urine areas. This equated to a 35% increase in DM production for the total area. The maximum difference between urine patches and controls was 1562 kg DM/ha in spring. Smaller differences were measured in summer (220 kg DM/ha) and winter (265 kg DM/ha). The maximum difference in CP was also in spring with 28.5% for urine patches and 19.4% for controls. DM production differences were attributed to net leaf photosynthetic rate, which ranged from 22.5 to 4.6 ¥ìmol CO2 m-2 s-1. On most days, leaf photosynthetic rate was not limited by environmental factors but in summer leaf photosynthetic rate was limited by both soil moisture (mean soil volumetric water content in the top 500 mm < 20%) and leaf N content (< 3 %N) compared with mainly low temperatures in winter (< 9 ¨¬C). Low temperature in winter also meant the duration of urine patch response was 133 days compared with 105 days in spring and 77 days in summer.