Effect of N and P fertilisation and their interaction on N:P-ratio of grass. June 20 th 2018, Jantine van Middelkoop

Transcription

1 Effect of N and P fertilisation and their interaction on N:P-ratio of grass June 2 th 218, Jantine van Middelkoop

2 Introduction Interaction between response to N&P fertilisation of grassland exists: optimum law of Liebscher: a production factor which is in minimum supply contributes more to production, the closer other production factors are to their optimum (explained by C.T. de Wit, 1992). To quantify N P interaction field trials took place Additional question: is N:P-ratio affected by N and P fertilisation level? Relevant (> statistically sign)? N:P-ratio is interesting Decide N or P is limiting in fertiliser recommendation In calculations or models where N or P is known, P or N is needed and not known Declare or evaluate mechanisms 2

3 Materials & Methods Data of 4 permanent grassland field experiments Sandy soil, marine clay, alluvial clay, peat soil Lolium Perenne dominated Cutting only (no grazing) Multifactorial design N P fertilisation mineral fertiliser 3 or 4 N levels: /4/45 4 P levels: 88/15 3 replicates 5 or 6 years on same plots Soil P < sufficient 3

4 Materials & Methods Observations a.o.: DM yield per cut N and P content per cut Calculations Annual DM yield, weighted average N and P content Annual N and P yield Annual weighted average N:P-ratio Statistical analysis: linear regression with fixed and random part, parameter estimation with Reduced Maximum Likelihood (REML) 4

5 Results: N and P yield (=Σ (DMY*content)) example: sand and alluv clay, avg over yrs kg N ha Sand, N yield 15 N Kg P ha Sandy soil, P yield 15 N kg N ha Alluvial clay, N yield N Kg P ha Alluvial clay, P yield 15 N

6 NP ratio NP ratio Results: N:P-ratio in 4 exp s, avg over yrs NP ratio Sandy soil N mod N mod 15 mod mod NP ratio Young marine clay mod 2 mod mod Alluvial clay N mod N mod 15 mod mod Peat N 15 N mod 15 mod mod 6

7 Results: Statistical model N:P-ratio Parameter Sand Marine clay Alluvial clay Peat Constant Nfertilisation Nfertilisation ns Pfertilisation #yrs Nfertilisation #yrs Ns Ns N Pfertilisation Pfertilisation 2 #yrs N fertilisation is positive and curves up at higher N level. Change in time: coincidence P fertilisation decreases N:P-ratio and stronger in time: P build-up in soil NxP decreases N:P-ratio: influence of P increases at increasing N fertilisation 7

8 Results: relevancy of NxP for N:P-ratio Model predictions: N fert: 15 and kg/ha P fert: 22 and 44 kg/ha N:P-ratio: Soil type 15 N 15 N P P 44P 44P Sandy soil Marine clay Alluvial clay Peat soil

9 Conclusions N:P-ratio is affected by both N and P fertilisation level and their interaction N increases, P and N P decreases the N:P-ratio The effect on N:P-ratio is relevant in magnitude General conclusions from the experiments: The effect of P-fertilisation increases in time by build-up of P in the soil in a period of 5 years The effect of N-fertilisation is not changing systematically in a period of 5 years; increase, decrease or no change seems to be a random effect caused by the productivity sequence of the years 9

10 Thank you for your attention Groeten uit Holland 1