Plant & Food Research Increased N efficiency in pastoral systems

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1 Plant & Food Research Increased N efficiency in pastoral systems Presented by Steve Thomas

2 Current research activities» Reduce N in forages» Better prediction of N mineralisation» Reduce N leaching losses» Reduce N 2 O emissions

3 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

4 LOW N CROPS

5 » 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

6 (a) Total nitrogen use efficiency TNUE (kg DM/kg total N available) Kale Fodder beet Maize Trade-off between yield (or N uptake) and Nitrogen Use Efficiency Nitrogen rate (kg/ha)

7 FORAGE CROPPING SEQUENCES TO REDUCE N LOSSES

8 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)

9 Timing is everything Delay in cover crop sowing: Limits growth rates Limits N uptake N leaching

10 BETTER PREDICTION OF SOIL N MINERALISATION

11 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

12 Current work ( )» Identify rapid, reliable method to estimate N mineralisation potential (measured in 14 wk 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

13 IRRIGATION MANAGEMENT TO REDUCE N LOSSES

14 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.

15 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 Urine EF Urine (EF3) 0.35% 0.15% 4% 3%

16 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

17 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) a) Lincoln climate (60 cm depth) c) Lincoln climate Irrigation (45 management cm depth) scenario Irrigation management scenario Otokia - Lincoln Templeton - Lincoln Eyre - Lincoln Nitrate leaching (kgn/ha) Nitrate leaching (kgn/ha) b) Hororata climate (60 cm depth) d) Hororata climate Irrigation (45 management cm depth) scenario Irrigation management scenario

18 REDUCING N LOSSES WINTER GRAZED CROPS (PASTURE RENEWAL)

19 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,

20 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 (d.f. = 11) Rape (IT) 2.4 Rape (NT) 2.5 New Pasture (P) (d.f. = 6) Post grazing - Treading/ - urine - Treading/ + Urine + Treading/ - Urine + Treading/ + Urine IT NT Approx. least significant ratio (5%) P (d.f. = 27) N leaching losses (1m) 15 to 40 kg N/ha. Lowest under treaded plots.

21 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

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