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Commercial cropping farms in New Zealand (NZ) showed highly variable rates of nitrate-N leaching losses (13–148 kg/ha/year) across sites, cropping systems and seasons. Losses were measured at 1.2 m below the soil surface using a network passive-wick drainage fluxmeters (DFMs) which were installed across nine commercial farms between August 2014 and June 2016. Sites were located in the Canterbury, Manawatu, Hawke's Bay, Waikato and Auckland regions and monitored for a period 51 to 72 months. Twelve DFMs were installed at each site and drainage volumes were validated using an established soil water balance model. At seven sites, losses were calculated using measured drainage and measured concentrations, and at two sites losses were calculated using modelled drainage and measured concentrations. Nitrate-N was the predominant form of inorganic N (96.7–99.9%) in drainage water and annual losses averaged 52 kg/ha/yr for mixed cropping systems with livestock grazing (n = 6) and 101 kg/ha/yr for mixed cropping systems with a focus on vegetable production (n = 3). While not broadly representative of all NZ cropping land uses, results from this study do, nevertheless, suggest that when drainage occurs, nitrate losses may be considerable under the land uses represented here (> 70 kg/ha/y). [ABSTRACT FROM AUTHOR]

Residual nitrogen (N) left in the soil following summer cropping or grazing by livestock is at risk of leaching in winter and spring. This study, conducted in Waikato, New Zealand, assessed the performance of different catch crop species and sowing dates in reducing the risk of N leaching. In 2016, Italian ryegrass and oats were sown in late March, April and May. In 2017, Italian ryegrass, oats and triticale were sown in mid March, April and May. In both years, urea fertiliser (400 kg N/ha) was applied immediately before the first sowing to simulate high N loading of the soil following crop grazing. Both years also included a fallow treatment (control) in which no catch crops were established. In both years, catch crops reduced N losses by 11–55% compared with fallow ground. Oats performed the best at earlier sowings, closely followed by triticale, while Italian ryegrass performed better at the later sowing. Sowing in March resulted in the highest reduction in N losses for all species. These results demonstrated that catch crops can be used to reduce N losses in these Waikato systems, and that species selection and sowing date are key to maximise their effectiveness. [ABSTRACT FROM AUTHOR]

Field trials conducted in the Waikato region over three summer seasons (2007–08, 2008–09 and 2009–10) evaluated whether soil nitrogen (N) reserves at sites previously under long-term pasture and with a history of regular farm dairy effluent application were sufficient for maize production with either minimal or no additional N fertiliser inputs. Crop productivity was assessed in the first (six trials) and second (two trials) years following cultivation of pasture. In first year trials there were no productivity differences between no fertiliser control treatments (NF) and treatments receiving an application of starter fertiliser (SF) or starter and side dress fertiliser (SSF). In second year trials the SF treatment maximised yield at one site, but none was required at the other. Crop yields were high across all trials (22.9–31.9 t DM/ha). Results confirmed that in most cases there was adequate soil N to maximise crop productivity without the need for fertiliser inputs. Despite high crop N uptake, soil mineral N levels remained elevated (109–227 kg N/ha) at four sites after cropping, an observation attributed to high rates of mineralisation during the summer. There were few correlations between pre-plant soil tests and the amount of N mineralised at these sites. [ABSTRACT FROM AUTHOR]

A closed incubation assay was conducted to identify attributes that can be used to predict nitrogen (N) supply from dairy cattle effluents applied to contrasting soil types. The experimental design included six slurry (DM 7.9–13%) and six solid (DM 15.9–42.5%) effluents applied to a Horotiu sandy loam or a Templeton silt loam with treatments incubated at 70% of field capacity at 20°C for 2, 5, 14, 21, 35, 42, 63, 96, 119 and 175 days. After 175 days, inorganic N supply (INS) ranged from −38.6 to 82.8% of total effluent N applied while net N mineralisation (NNM) ranged from −107.4 to 65.1% of organic effluent N applied. The best predictor of INS at day 175 was the log ratio of total C to water extractable N (P < 0.001, r = −0.85) and the log ratio of DM to water extractable N (P < 0.001, r = −0.85) (water extractable N = water soluble N + hot water extractable N). These measures were inversely related to INS and effective at explaining both net mineralisation and immobilisation effects. Importantly, correlations between INS and C:N ratio measures were improved considerably when total N was substituted for a labile N measure, in this case water extractable N. We were unable to identify an effluent measure to consistently predict NNM. [ABSTRACT FROM AUTHOR]

Nitrate leaching from soil is a major problem in New Zealand pastoral systems, requiring development of practical methods to manage accumulation of nitrates. Nine feed trials were carried out in the Waikato (n = 3) and in Canterbury (n = 6) between 2013 and 2016; from which 424 samples were selected for forage quality testing. Only tick beans and forage rape met the lactating feed criteria for adequate crude protein (CP; > 16% DM) and soluble sugars and starch (SSS; > 25% DM). When an 'environmental' criterion was added to a feed value for lactating cows this reduced the options to fodder beet only. However, the CP measurements for fodder beet were suboptimal for milk production, requiring the fodder beet to be mixed with high protein feeds such as pasture or pasture silage. The lower protein requirements for non-lactating cows, including an additive environmental criterion enabled a wider range of feeds to be considered e.g. kale, sunflowers and swedes in Canterbury (12 entries) and fodder beet and rape in the Waikato (21 entries). Addition or restriction of nitrogen fertiliser was the only agronomic management intervention that consistently altered animal feed quality and potentially changed N excretion. Crop choice was likely to have the greatest impact at the farm level. By limiting feed quality assessment to CP, SSS and their ratio (SSS:CP) we were able to define a selection/feed monitoring method to minimise N content of feed, maximise SSS feed value and limit excess N intake to reduce the nitrate leaching risk. [ABSTRACT FROM AUTHOR]

The effects of winter crop selection, timing of harvest dates for the winter crop and sowing date and hybrid duration for maize crops on total biomass and feed quality for spring-winter crop sequences were investigated. Two sets of experiments were established in each of Canterbury and Waikato regions of New Zealand in 2009-2010 seasons. Winter cereal crops, specifically oats, were more productive, than legumes and Italian ryegrass. Delaying the sowing of maize resulted in increased biomass production of the whole sequence by harvesting more of the spring production of the intervening winter crop. However, delayed harvest of winter crop resulted in declining energy content. Winter grazing decreased the accumulated dry matter production by between 1.3 and 5.2 tonnes dry matter ha−1. The overall results confirm the findings of the earlier simulation study, with delayed maize sowing in order to harvest more biomass from the winter crop increasing yield of the whole sequence. [ABSTRACT FROM AUTHOR]

Conflicting reports of the responsiveness of carrots (Daucus carota L.) to nitrogen (N) fertiliser have been rationalised on the basis of the climatic zones in which the experiments were conducted. We tested this explanation with two experiments under temperate conditions, where yield increases were predicted to be unlikely, yet growers frequently apply N fertiliser. Our results show that in temperate regions carrot yields may indeed respond to N fertiliser when the yield potentials are c. 140 t ha−1 of fresh roots, if soil mineral N to 0.6 m depth and readily mineralisable N add to less than c. 190 kg N ha−1. With normal experimental precision, such responses may be undetected unless soil water deficit is kept small and variations in plant population are accounted for. Carrots have strong potential for luxury uptake of N. This has implications for marketing and the possible use of carrots as catch crops. [ABSTRACT FROM AUTHOR]