Thermal Time as a Parameter to Determine Optimal Defoliation Frequency of Perennial Ryegrass (Lolium perenne L.) and Pasture Brome (Bromus valdivianus Phil.)

Iván Calvache,Oscar Balocchi,Ignacio F López,Máximo Alonso,Juan Pablo Keim

doi:10.3390/agronomy10050620

Iván Calvache, Oscar Balocchi + Show 3 more

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https://doi.org/10.3390/agronomy10050620

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Journal: Agronomy	Publication Date: Apr 27, 2020
Citations: 12	License type: CC BY 4.0

Affiliation: Austral University of Chile, Massey University

Abstract

The herbage mass and nutritional value of harvested forage are fundamental determinants of the production potential of pastoral systems. The objective of this study was to evaluate the growth dynamics and accumulated herbage mass expressed in dry matter (DM) of perennial ryegrass (Lolium perenne L.) and pasture brome (Bromus valdivianus Phil.) pastures, using thermal time (TT) as a defoliation criterion. Thirty plots (15 of L. perenne and 15 of B. valdivianus) were distributed in three field blocks and subjected to five defoliation frequencies (DF) determined by TT, expressed as the accumulated growing degree-days (AGDD; DF1 = 90, DF2 = 180, DF3 = 270, DF4 = 360, and DF5 = 450 AGDD) for one year (2016), at the Austral Agricultural Experimental Station of the Universidad Austral de Chile. Every three days, the total leaf length (TLL) was measured, and the leaf elongation rate (LER, cm L−1), leaf growth rate (LGR, cm L−1), leaf appearance rate (LAR, d L−1), phyllochron (AGDD L−1), and accumulated herbage mass per hectare (kg DM ha−1) were calculated. Defoliations were scheduled according to AGDD, and a sample was taken from each cutting to determine (dry matter ‘DM’, crude protein ‘CP’, neutral detergent fiber ‘NDF’, acid detergent fiber ‘ADF’, water-soluble carbohydrates ‘WSC’ and metabolizable energy ‘ME’). The pastures that were allocated to DF5 presented higher DM yields (12,600 kg DM ha−1 year−1), TLL (54.6 cm), and LER (0.63 cm d−1) compared to pastures with high DF (90 and 180 ADGG). B. valdivianus presented a lower phyllochron than L. perenne (74.4 vs 87.9 AGDD L−1, respectively). Concentrations of CP and ME decreased from the shortest DF (90 AGDD) to the largest DF (450 AGDD), dropping from 221 to 138 g kg−1 CP and from 2.6 to 2.4 Mcal kg−1 DM of ME. All variables were affected by the season (Ssn) (p < 0.001). The AGDD can be used as a defoliation criterion and a tool to balance yield with nutritive value according to the farmer’s needs.

Highlights

Defoliation frequency (DF) is an important factor that influences recovery of pastures to grazing events [1]
The results of this study show that growth, development, and nutritional value of both L. perenne and B. valdivianus can be modified by defoliation frequencies (DF)
This study shows that B. valdivianus required 13.5 accumulated growing degree-days (AGDD) for new leaf appearance, which affirms the theory that the phyllochron is very dependent on the phenological stage of each Sp and must be determined for each Sp [12,38]

Summary

Introduction

Defoliation frequency (DF) is an important factor that influences recovery of pastures to grazing events [1]. Several studies reported that DF affects pasture dry matter (DM) yield, regrowth rate, and nutritive. Frequent defoliation has been shown to reduce persistence of perennial ryegrass, DM yield, and nutritive value when compared with infrequent defoliation [2,3]. The phyllochron value is measured in accumulated heat units, a value that remains constant under different daily temperature regimes [5]. In cool-season grasses, temperature is one of the main atmospheric factors that influences pasture growth and development, especially in Sp that need to accumulate chilling hours to progress from the vegetative to reproductive stage [6].

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