Plant & Food Research Increased N efficiency in pastoral systems Presented by Steve Thomas
Current research activities» Reduce N in forages» Better prediction of N mineralisation» Reduce N leaching losses» Reduce N 2 O emissions
Forage for reduced nitrate leaching (FRNL) Programme Two key research themes:» Crops to reduce urinary N excretion and losses» Management of soil, crop and effluent to reduce N losses
LOW N CROPS
» Hypothesis: Forage crops can be selected that are high yielding and low N to reduce urinary N losses.» Which crops?» E.g. Fodder beet = low N concentration» Kale, Sunflower, Fodder beet, Cereals, Sorghum, Rape, Maize, Chicory» Mixtures?» How best to grow them?» Optimum fertiliser N for range of forages
(a) Total nitrogen use efficiency TNUE (kg DM/kg total N available) 300 250 200 150 100 50 Kale Fodder beet Maize Trade-off between yield (or N uptake) and Nitrogen Use Efficiency 0 0 200 400 600 Nitrogen rate (kg/ha)
FORAGE CROPPING SEQUENCES TO REDUCE N LOSSES
Crop sequences to mop up N (e.g. Silage Maize > Green-feed Wheat) Hypothesis: Timing, crop types and sequences of crops can be adjusted to reduce N losses. APSIM modelling: Two initial simulated soil mineral N loads: Green-feed wheat (silage) Maize silage Low initial soil N (150 kg/ha) High initial soil N (650 kg/ha)
Timing is everything Delay in cover crop sowing: Limits growth rates Limits N uptake N leaching
BETTER PREDICTION OF SOIL N MINERALISATION
Predicting N mineralisation Hypothesis Better prediction of soil N availability can lead to improved fertiliser NUE (reduced N losses) pasture and forage crops Mineralised N: important N source; difficult to predict Parfitt et al: N mineralisation vs pasture growth
Current work (2014-15)» Identify rapid, reliable method to estimate N mineralisation potential (measured in 14 wk incubation @25 o C/field cap.» Literature search carried out to select candidate assays (9)» Wide range of soils (120)» 5 Soil Orders» 4 Management history» Cropping & pasture» Different textural classes» Wide range of soil organic matter
IRRIGATION MANAGEMENT TO REDUCE N LOSSES
SLMACC funded Irrigation and N 2 O» Hypotheses:» Better management of irrigation will reduce N losses (gaseous and leaching) while maintaining pasture production.» Reduction in losses will strongly depend on irrigation and grazing management, soil and climate.
Effects of irrigation frequency on freelydrained versus poorly-drained soil N treatment Cumulative N 2 O emissions (kg N ha -1 ) Irrigation Frequency Canterbury Freely drained Otago Poorly drained 3-day 15-day 3-day 15-day Control 0.43 0.18 0.3 0.2 Urine 2.45 1.12 24.6 19.0 EF Urine (EF3) 0.35% 0.15% 4% 3%
N losses from irrigated pasture on shallow free draining soils Lysimeter trial no rainfall inputs and full irrigation Summer leaching below urine patch 19 to 30 kg N/ha in 50 mm of drainage = 3 to 5 % of applied urine N Difficult to manage drainage from irrigated shallow soils (add effects of rainfall). Drainage losses from shallow, freely draining soils can be both rapid and large 12-14% of applied urine N leached over 8 months N 2 O losses were comparatively low - 0.5% of applied
Irrigation and N losses from soils of differing drainage and water holding characteristics APSIM Simulated N leaching losses under urine patches (600kg N/ha) Soils: Shallow freely draining (Eyre) Deep freely draining Deep poorly draining (Otokia) Irrigation: 6 trigger deficits, 3 application amounts Rainfall 2 rainfall regimes (600 and 800 mm per year) Nitrate leaching (kgn/ha) Nitrate leaching (kgn/ha) 250 200 150 100 50 0 300 250 200 150 100 50 0 a) Lincoln climate (60 cm depth) 1 2 3 4 5 6 c) Lincoln climate Irrigation (45 management cm depth) scenario Irrigation management scenario Otokia - Lincoln Templeton - Lincoln Eyre - Lincoln 1 2 3 4 5 6 Nitrate leaching (kgn/ha) Nitrate leaching (kgn/ha) 250 200 150 100 50 0 300 250 200 150 100 50 0 b) Hororata climate (60 cm depth) 1 2 3 4 5 6 d) Hororata climate Irrigation (45 management cm depth) scenario 1 2 3 4 5 6 Irrigation management scenario
REDUCING N LOSSES WINTER GRAZED CROPS (PASTURE RENEWAL)
Winter forage grazing (pasture renewal scenario)» Potentially large N leaching and N gaseous losses from grazed forages» Hypothesis;» N losses from winter grazing are reduced using no-tillage practices to establish crops and pasture»lincoln.»intensive tillage,»no till»rape»ryegrass»poorly drained soil,
Cumulative N 2 O and N leaching losses Herbicide Precultivation (41 d) Post-cultivation to Pre-grazing (128 d) l.s.d. (5%) Post spray Old pasture 0.03 Sprayed off pasture 2.2 0.95 (d.f. = 11) Rape (IT) 2.4 Rape (NT) 2.5 New Pasture (P) 1.8 0.9 (d.f. = 6) Post grazing - Treading/ - urine - Treading/ + Urine + Treading/ - Urine + Treading/ + Urine IT 15.2 58.0 49.0 109.8 NT 8.2 37.9 7.4 46.0 Approx. least significant ratio (5%) P 0.4 33.7 0.4 28.7 1.3(d.f. = 27) N leaching losses (1m) 15 to 40 kg N/ha. Lowest under treaded plots.
Other N research» Closed loop nutrient management effluents on crops.» Microbial and fungal ecology and denitrification» SFF dairy wintering systems» Urine composition and transformations» Spatial N management» SFF - West Coast N use efficiency on West Coast humps and hollows and flipped soils
www.plantandfood.co.nz Steve.thomas@plantandfood.co.nz