Effects of different forages on the yield and composition of cereals within a rotation: Extended abstract

Legumes and other forages may contain higher concentrations of minerals than ryegrass (Marley et al 2013), which may help to develop sustainable approaches to the management of these nutrients within agricultural systems. There has been extensive work on the effects of previous legume crops on N utilisation by a subsequent cereal crop but there have been fewer studies on other minerals essential to crop health. Cultivation is known to change the availability of nutrients within soil, with previous research showing differences amongst cultivation techniques in their effects (Canell et al 1980).
Here, a study examined the effects of previous forage crops on the yield and mineral concentration of the grain and straw from a spring wheat (Triticum aestivum) crop followed by a winter barley (Hordeum vulgare) crop. Four replicate plots (12m x 7.5m) of perennial ryegrass (Lolium perenne), chicory (Ch)(Cichorium intybus), red clover (RC)(Trifolium pratense) and white clover (WC)(Trifolium repens) forages were established as pure swards in June 2009 in a randomised block design. Forages were harvested five times per annum during 2010-2012 and forage removed. Ryegrass plots received either low nitrogen (LowN PRG) or nitrogen at a rate of 200 kg N ha-1 year-1 (HighN PRG) and chicory plots received nitrogen at a rate of 200 kg N ha-1 year-1.
Soil samples taken prior to wheat establishment showed no effect of previous forage cropping on soil pH or ammonium-N, P, Ca, Mg, Na, B, Cu or Zn concentrations. Soil nitrate-N concentrations were significantly lower in both PRG treatments when compared with WC and Ch. Soil K concentrations was significantly lower in both PRG treatments when compared with Ch. Soil Mn concentration was lower where Ch was grown compared to PRG.
Forages were killed-off using a non-selective herbicide in spring 2013 before each plot was split and wheat was established either after ploughing (Pl) or by direct drilling (DD). On 5 April, spring wheat (cv. Tybalt) was sown on all plots using a Duncan Ecoseeder at a rate of 253kg ha-1. Fertiliser was applied at a rate of 176kg N, 31 kg P2O5, 105kg K2O and 58kg SO3 ha-1. Prilled lime was applied at 370kg ha-1. Plots were harvested on 29 August, using a Sampo harvester and the grain and straw removed.
On 15 October, winter barley (cv. Pearl) was established, at a sowing rate of 196kg ha-1, using the same two establishment methodologies and plan used previously for wheat establishment. The following spring, fertiliser was applied to the barley at a rate of 132kg N, 66 kg P2O5, 97kg K2O and 24kg SO3 ha-1. Prilled lime was applied at 370kg ha-1. Plots were harvested on the 15 July 2014, using a Sampo harvester, with grain and straw removed.
For both wheat and barley, grain and straw yield were assessed. Grain and straw mineral analysis was conducted by Inductively Coupled Plasma-Optical Emission Spectroscopy. N & S were determined by the Dumas Technique. Data were analysed by ANOVA as a split plot using Genstat® 11.1. Multiple comparisons were based on Bonferroni adjusted LSDs.

In the first cereal harvest (spring wheat) after each forage treatment, there was no effect of previous forage (PF) treatment on wheat grain or straw yield. Establishment method (EM) had no effect on straw yield (6344 and 6328 kg DM ha-1 for DD and Pl treatments respectively) but DD resulted in a significantly higher grain yield when compared to Pl (P=0.032) (6936 and 6640 kg DM ha-1 respectively).
PF affected the total mineral offtake of N, P, Mg and S in the subsequent wheat crop as grain and straw. Offtake of N, Mg and S was significantly higher following WC when compared with HighN PRG. Offtake of P was significantly higher following LowN PRG when compared with RC. N offtake from Pl treatment was significantly higher than DD (P=0.016)(199.7 and 193.2 kg ha-1 respectively). K offtake was significantly higher from DD treatment compared to Pl treatment (P=0.002)(83.6 and 73.9kg ha-1 respectively). Cu offtake was significantly higher from DD treatment compared to Pl treatment (P=0.004)(47.8 and 45.6g ha-1 respectively).

By the second cereal harvest (winter barley), barley grain yield was not affected by PF but straw yield was significantly higher following Ch when compared to RC (6634 and 5904 kg DM ha-1 respectively) with LowN PRG, HighN PRG and WC intermediate. EM had no effect on straw yield (6214 and 6251 kg DM ha-1 for DD and Pl treatments respectively), nor overall grain yield (9012 and 9202 kg DM ha-1 for DD and Pl treatments, respectively). The Pl Ch treatment had a significantly higher grain yield than DD Ch (9304 and 8685 kg DM ha-1 respectively).
PF had no effect on macro mineral offtake as barley straw and grain. Pl resulted in a significantly higher Cu offtake when compared with DD (P=0.014)(49.1 and 46.9g ha-1 respectively).

The findings of this study confirm previous work showing the effects of previous forages on N uptake and utilisation by a subsequent cereal crop and also the extent to which other minerals are affected by cropping rotations and cultivation methods. These findings have started to unravel some of these effects to enable the development of more sustainable approaches to the management of these nutrients within agricultural systems.